Star tuned Magazine December 2013

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Information about Star tuned Magazine December 2013

Published on February 4, 2014

Author: RBMParts



StarTuned Magazine, December 2013

Your Workshop Resource to Get the Job Done • WIS-net (Workshop Information System) • Wiring Diagrams • Technical Bulletins • Maintenance Sheets • Star Diagnosis System (SDS) • Mercedes-Benz Workshop Equipment • Mercedes-Benz Special Tools @ Mercedes-Benz

TO OUR READERS: IN THIS ISSUE Welcome to STARTUNED, the magazine for independent service technicians working on Mercedes-Benz vehicles. Your MercedesBenz dealer sponsors STARTUNED and provides the information coming your way in each issue. Mercedes-Benz wants to present the information you need to know to diagnose and repair Mercedes-Benz vehicles accurately, quickly and the first time; text, graphics, on-line and other technical sources combine to make this possible. Feature articles, derived from approved company sources, focus on being useful and interesting. Our digest of technical information can help you solve unanticipated problems quickly and expertly. We want STARTUNED to be both helpful and informative, so please let us know just what kinds of features and other diagnostic services you'd like to see in it. We'll continue to bring you selected service bulletins from Mercedes-Benz and articles covering the different systems on these vehicles. Send your suggestions, questions or comments to us at: STARTUNED One Mercedes Drive Montvale, New Jersey 07645 Phone: 1 201.263.7284 E-mail: 4 In order to maintain emissions compliance, Mercedes-Benz engineers have to control the temperature range the engine will operate in and develop engine management parameters within this range . This may sound simple enough, but how do you accomplish this when the car might sit for an hour of traffic on a hot summer day, or cruise at highway speeds in the dead of winter? 12 Technical Advisor Christopher M. Ayers, Jr. Tim Amun Editorial Director MERCEDES-BENZ CDI DIESELS: No MoRE KNOCKING, SMOKING, OR STINKING Unstable fossil-fuel markets, customer environmental awareness, and government regulations have all contributed to automobile manufacturers searching for the silver bullet fo!i mpg. Mercedes-Benz has looked to its long diesel engine history, and added a huge dose of new technology. STARTUNED is a publication of Mercedes-Benz USA, LLC ("MBUSA"). No part of this magazine may be reproduced without the express written permission of MBUSA. Editorial and Circulation Offices: 1348 River Road, Montague, NJ 07827. CAUTION: Vehicle servicing performed by untrainedpersons could result in serious injury to those persons or others. Information contained in this magazine is intended for use by trained, professional auto repair technicians ONLY. This information is provided to inform these technicians of conditions which may occur in some vehicles or to provide information which could assist them in proper servicing of these vehicles. P roperly trained technicians have the equipment, tools, safety instructions, and know-how to perform repairs correctly and safely. If a condition is described, DO NOT assume that a topic covered in these pages automatically applies to your vehicle or that your vehicle has that condition. STARTUNED is aregistered trademark of MBUSA. Group Publisher NARROWING THE RANGE OF TEMPERATURES WITH THE E-fHERMOSTAT Donald Rotolo Bob Freudenberger Contributing Editors Bob Chabot Michael Klaas Tom Nash Frank Walker 22 MBUSA Technical Content Advisor MEET THE CLA, MODEL SERIES 117 Big news from Mercedes-Benz! Not only front wheel drive and MacPherson struts, but also a host of other departures that prove the superiority of the company's forward-thinking engineering. MBUSA Project Manager Stefanie Schweigler Art Director & Circulation Mgr. Christopher M. Ayers Ill ayersc3@ Cover photo: 2014 CLA250 (courtesy Mercedes-Benz} Visit us at our web site to view this issue and all past issues of StarTuned, along with a wealth of information on Genuine Mercedes-Benz Parts. To locate a Mercedes-Benz dealer near you, go to 28 FWD & MACPHERSON STRUTS CHANGE THE COLLISION REPAIR GAME Many advanced steering, stability control, and propulsion technologies in the front-drive CLA depend upon precise suspension geometry for proper vehicle operation. Here are some front wheel drive suspension basics for collision repairers who will be working on this history-making model.

When most of us think of technologica l developments, we don't think about cooling systems. We think about high-speed CAN data buses th at al low the traction control system to work with the electronic throttle to rein in a vehicle. We may even think about fiber-optic systems that carry music, mov ies, and media for entertaining our passengers, and providing nav igation. We think about electroni ca lly fueli njected hi gh-horsepower engi nes that sti 11 get 25 to 30 mpg. Now think about a typica l ca r being driven in a temperate cl imate that may sit for an hour in an urban traffic jam on a 100 deg. F. day. Th is sa me car may need to ca rr y its owner to work in si ngledigit temperatures on a February morn i ng. A car 's cooli ng system does more than ju st prevent t he engine from overh eating. It keeps it within the temperature ran ge required to promote optimum efficienc y and emi ssions control, and to allow long life for mechanical components. Engineer s design engines to work best within a specific temperature range. The engine management system uses coolant temperature as a reference for controlling fuel deliver y and ignition tim i ng. The pistons, r ings, va lve stems, This is the e-thermostat location on a 221 chassis with the V12 engine. It is buried under the Secondary Air Pump motor and behind an idler pulley for the drive belt. WIS can help you with both testing and service procedures. December 2013 5

bearings and other intern al engine parts will have ex panded to the tolerances that wi ll maximize the li fe of al l components. The cooling system's job is to keep the eng i ne operating in that temperature w indow as much as possible. Think of our example of a ca r bei ng driven in traffic on a hot day. Most of the ai rfl ow over the rad iator fin s would be onl y what's ava ilable from the cool i ng fans. So, the therm ostat opens all the way to allow the maximum volume of coolant flow. On a cold day at crui si ng speeds, the heat load is low, and so is the temperature of t he coolant in t he rad iator. The therm ostat will close as its element shrinks, coolant fl ow is decreased. Thi s is how engine temperatu re was maintained in its "Temperate Zone" for decades. 1 c • • • • • •• ... .... # ... - • • # • I "r"--~---~-~·-- •.-· •• I • I e: I I I WHAT'S AN E-THERMOSTAT'S PURPOSE? To adhere to specific fu el mileage and efficiency standards, engi nee rs needed t ighter control of the engine's temperature. For the M272 engine, Mercedes-Benz developed a more adva nced .......... I Right: In phase 3, the engine control unit starts to energize the heater coil in the e-'stat and heated coolant from th e engine block (passage 2) can either flow through passage 3 (to the water pump), or now to the radiator through passage # 1. V1hldlK1•rcAt:•*ftUft'IOtr ~ l11H ll Ill W8 Cl'IH &ltmoot '"' CNt • 1 Ot' f"'*'Hl rtl'ICr!llM . # • ...... I 3 · I.___ __ _ __ ___, 16U M ML. l$0 4MA.TIC • l7lte7 • A0 722t!le W7 C700 • 2.Stanau rth *R'*MF · ID g ic~1ooc.-nttt · I ~ © ~ · - · aD I ~ O;;; ~ F•;•""°' vau.:,°' P1~11or2 BooQMM ~ ~~=:::~~~------------~ I24.9.09 I EPC Use to access WIS. This will give you all the steps needed to service the e-thermostat. Here, we have looked up the procedure on a 164 chassis M -Class with the 272 engine. 6 Mercedes-Benz StarTuned

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thermostat that can control engine temperature accurately in mu ltiple situations. It still functions like a traditional thermostat with an ex pand i ng/ contracting element that opens and closes according to coolant temperature, but it has three disk s (meaning the thin, round meta l pl ates th at altern ately cover and uncover coolant passages) instead of the normal single disk to graduall y step coolant fl ow, and a computer-controlled heating element. The three disk s prov ide four di fferent stages in openi ng the thermostat. Each stage regulates the coolant tlow to match the cooling prov ided by the radiator and the needs of the engine. A ny thermostat, even the "e-'stat," has a full y closed position when the engine is cold to build up coolant heat quick ly. Rapidly reaching normal operati ng temperature allows cr itical mechanica l components to ex pand to th eir idea l work i ng shape as soon as possible, and speeds the transition to closed-loop operation. You can measure the resistance of the heating Think of the e-therm ostat as hav ing one si ngle element in the e-thermostat to see if it's okay. A good one will have about 14.7 to 15.0 ohms at upper di sk and two staggered lower disks. The room temperature. The electrical connection is upper disk di rects coolant flow to the rad iator, and a little difficult to get to, so you may want to put the lower disks can either al low coolant to be spl it your test leads across one of the wires that share between the eng ine and the radiator, or totally the po wer supply and the pin on the ME control block flow to the engine forci ng all of the coolant unit that g rounds it. flow through the radiator. During a •• cold start, both the ' upper disk and one of the lower di sks total ly block coolant fl ow allowing the engine to bu i Id heat rapid ly. The heat of .,,. "' the engi ne coolant opens the fi rst stage supply i ng the heater core in the cabin . In the th i rel stage, the computer controls the current flow i ng ,. " th rough a heater Here we are looking at the electrical control of the e-thermostat. The upper blue element inside the trace is the voltage signal. The lower brown trace is the amperage draw. Soon after body of the e-'stat. a hot restart, the ME grounds the element for a fe w seconds and we can measure This assistance th e amperage dra w. If amperage draw is too lo w or too hig h, the e-thermostat has occurs on both a probably failed. Mercedes-Benz Sta rTuned 8 .. Cl( .. .. ... ... ... . ..

hot resta r t where the eng i ne temperature reads over 208 deg. F. (98 deg. C), or after a cold start where t he engi ne temperature is about 82 deg. F. (28 deg. C). WHEN THE ME IS IN COMMAND The ME control un it (aka the PCM for Powertrain Control Module, or engine management computer) can r egulate the temperature bet ween 185 deg. F. (85 deg. C) to 22 1 deg. F. (105 deg. C) wh ile the engine is runn in g. Above these temperatures, the ME com ma nd s t he thermostat to block coolan t flow back into the engine, directing all coo lant flow to the radiator for maximum cool i ng. ts you can see, wi th cooling temperatures reaching above 221 deg. F. (105 deg. C), and the boiling poi nt of water being 212 deg. F. (100 deg. C), it is critica l that the mixture of Mercedes-Ben z extended l ife ® Me1~edes-Benz A~ticorrosion/ Antifreeze AGENT Pro1ec1i aqo Ir tadlator ano Can,,tezJno ano raJ engine lrom corrosion lat Se~~:eo~ lo MerceJ::.Jha boiling polnl. rooucts sheet N Specifications anz o. 325. 0 P 111 Hurnbtr !~ 1030004 ""'-c; ""°"·l~LllRES ~°'"'""' ""'-lOWto '--..uo . ...... It makes no sense to use anything but genuine Mercedes-Benz antifreeze for cooling system service. The current blue-dyed formula carries the part number BO 1 03 0004, which is also designated as G48. It only comes full-strength, not pre-diluted. coolant and water be i n the proper dilution ratio to transpor t Btus efficien tly. The fundamental functions of the cooling sys tem must be worki ng properl y for the e-thermostat system to be able to do its job. The water pump must stil l be capable of provid i ng sufficient flow, and there cannot be any air in the system. When diagnosing and se r vici ng these systems, do not j um p to testing this new technology until you have done some basic checks, such as pressure testing. The e-thermostat gets its voltage supply from power dist ribution compone nts such as the front SAM. The ME controls t he ground with a pulsewidth modulated signal. It determines how much cu rrent should fl ow t hrough the heat ing element usi ng coolant temperature, engine speed, engine load, and vehicle speed as references. You ca n mon itor the vo ltage signal and curr ent flow directl y, or you can monitor e-t hermostat operation through Xentry software. vlhile it is possible to test the element at t he therm ostat itself, in most instances it is difficu lt to get to and may require tha t some components to be removed . What may be easier is to measure the resistance, voltage and current at the ME. Looking at a wiring diagram available on www.startek, you can identify the grou nd pi n locat ion at the ME and put your other lead on one of the shared power suppl y wires. STAGES The ME controls thee-t hermostat in three stages. It ca n leave t he heat ing element alone by not provid ing any g round. Without a ground, the circuit is incomplete -- there is no current fl ow and therefore no e-thermostat activ ity. Or, the ME can pulse the ground thereby heating up the element to a specific temperature and maintaining th at temperature. It can also ful ly ground the element to allow maximum current fl ow, thus generating the max imum heat the element is capable of. You ca n monitor th is ci rcuit for vol tage and amperage. As the wi rin g diagram shows, you shou ld find batter y vol tage on t he circu it when the ME is not g rounding the element. When the ME star ts to ope rate thee-therm ostat, you may see your read ing go directly to ground, or find a pulsew idth modu lated sig nal. Hemember, the pulsew idth moclulated signal holds thee-thermostat December 20 13 9

in a static position to regulate the coolant tlow between 185 deg. F. (85 deg. C) and 221 deg. F. (105 deg. C). I f you measure the current tlow w hile the e-thermostat is being grou nded, you shou Id see about 7/ I Oths of an amp (0.7A). I f you measu re directly, t he meter wi ll probably average the signal over time so you w ill see less amperage wh ile the signal is pulse-width modulated . You w i II have to wait for the eng ine to run long enough to full y ground thee-therm ostat to measure the amp draw accurately. If you use a scope w ith an i nduct ive m illiamp probe, you can monitor both the voltage and amperage at the same time. A lmost immediately afrer a hot resta r t, the ME operates thee-thermostat for approximately six second s, du rin g w hich time you ca n eas il y r ead the voltage and amperage. I f you are usin g Xentry software to v iew the computer 's management actions, it w ill g ive you a data PIO to evaluate the comma nd s to thee-thermostat. IT'S STILL A COOLING SYSTEM As mentioned earli er, ever y other aspect of t he coolin g system must be function ing properly for the e-thermostat to be able to do its important job. ~· If you're doi ng a flush and refill as maintenance, or w henever you've done any major cool ing system worl< that required dra i ning, it's recommended th at you use coola nt exc hange equ ipment. Not only is it a lot fa ster and neater, it does a much better j ob of completely fl ushing the ent ire system, el iminates trapped ai r that can cause various troubles, ensures a complete fill, and even helps you find lea ks. By the way, thee-thermostat has a check ba ll to al low ai r to pass through it during th e fillin g. Of course, to keep t he ca rs i n you r care troublefree, always follow the cool i ng system maintenance i nter vals stated i n the Owners' Manual or on WIS to the letter, and use on ly genuine Mercedes-Benz antifreeze for top-ups and refi lls. Know in g how a system functions and w hat you can do to ser v ice it is what keeps your customers comin g back. By purchasing genu i ne MercedesBenz pa rts from your dealer you have a partner i n the ma intenance of your customers' veh icles who not onl y suppl ies properly-engi neered parts, but also offers the best wa r ranty in the i ndustry. Who would n't wa nt a partner li ke t hat? I :::- · 1 .J !p91:1Ip EM1f!t 1 J 1 /> eltlOuaoout l!W!f1'UlpQ• Q? '"9' '~'lt'"t:Y-'C" S::: ., A 1nlOOOlU O.UtM"IAI r ~br. A2122'000.&tS J IPPI p10 prn raornzt Jt'l>S1iH ~· l)MlfnnfMQ l!QQWHfremDt r 50 ACIDD9Hl20) • Dflt Wls...DIC r 60 A mlDJ CO., . CAs&rl 1lfJtN)$'1AJTOTM«:OCA!Z SC&)6~.. . . I- - - - r 60 A mJOJOUO 00 1 ~ fPM]IQ fM!!t'.!OOW21IpDMtOZ · ~ _ CIO I THJtNZTAT 10 1lMM: ~ 1-- ----~ !0C?!! EC2!!! ED'Z'f r r ,. r IO '.Xrn-"'J.! rrmo1 "' 090 .J !5!0l!I9 Enzr1 )9Ct".tOl l1PN 0'2 ....... o~ "°"""" ..J ~ l:l.J!.la_ HQOOOQ000 111, HUAlOIUlAA 80l.1 00) nOHOST.t.T fO BCH;CA2 Mfill.U r ., ...... .J e"?fllsf11-• w u uraprr (I? TtOMOS'TATTO TMt«; CJ«. IO-----J &r?! [t90f~t )9!?!.11Hfr;:mQ1 r L:io • 2n mo:n 1 VAl'rt C'l'l.HXJl tUD, LD'l u:AA .,,~ .:J Use Mercedes-Benz EPC to assist you in identifying the proper part. While you should always trust the knowledge of the parts man at your local dealer, EPC will help you identify other parts you may want to replace during the job, such as a new electrical connector if the old one was damaged. 10 Mercedes-Benz StarTu ned

Mercedes-Benz CDI Diesels No More Knocking, Smoking, or Stinking 12 Mercedes-Benz StarTuned

Unstable fossjj-fuel markets, customer envjronmental awareness, and government regulaUons have all contrjbuted to automobile manufacturers sear ching for the silver bullet for mpg. Mercedes-Benz has looked to Us long djesel engjne hjstory, and added a huge dose of new technology. Ask powertrain engineers and they wi ll all tel l you thei r ultimate goa l is " the free lunch." Of course, Ii ke the physici sts' Absolute Zero, that's not rea ll y attainable, but it at least provides a clea r direction. The goa l of an engin eer is to optimi ze an intern al combustion engine's output in order to produce max imum power while usin g the mini mum amount of fuel. Approaches such as turbocharging, variable va lve timing and lift, direct fuel injection, etc. all contribute to this mai n objecti ve.) There's a concept that goes even furth er, however: compression ignition. Diesels have always sq ueezed more u seful work out of a ga llon of fuel th an gasoline-burning engines, and w ith Mercedes-Ben z's application of adva nced tech no logy t hei r inherent draw backs in term s of noise, smel l, emi ss ion s, cold sta rtin g, and lacklu ster perform ance have all been pretty much elimin ated. This ar t icle is intended to help you keep up w ith t h is tech nology so that yo u'll have a better understanding of the ser v ice req uirements invol ved. SINCE 1936 Mercedes-Benz has always felt that the diesel engi ne has tremendous adva ntages when it comes to incr easing fuel economy and reducing harmful emi ss ions, although on ly the former was germ ane in 1936 when the compa ny introduced the 2600, the world's first diesel passenger ca r. It has successfull y sold diesels to the A mer ican pub! ic for decades. With the modern push for fu el effi ciency and clean ex haust, Mercedes-Benz has pract ica ll y reinvented the compression ignition engine. Elect ron ical I y-control led high-pressure di rect injection and an after-combustion cataly tic system are just t wo of its prominent advances. December 2013 13

But revolutionary engineerin g improvements rarely come w ithout additional levels of techn ical complex ity, which makes our job of keeping ever ythin g operatin g properl y challeng ing. A/e believe, however, that you will find that your ex perience w ith the electron ic management systems of gasolineburning eng ines w ill be ver y helpful. MAJOR PSI With a paid subscription to, y ou can access function Th e Mercedes-Ben z diagrams in the ETM section. These let you know wha t sensors and control CDl (Common rail Direct units ar e involved in the system you are working on. This is a function Injection) system has diagram of the smooth-running system on the 642 diesel engine. The an elect r ic fu el pump CD/ control unit looks at all of these components to mitigate crankshaft that supplies relati vely fluc tuations through individual cylinder injection control. low pressure, but h ig h volume, to the mechanica l high-pressure pump that's driven by a camshaft. The 5,000 to 30,000 psi (!) generated is routed th rou g h a common rai I t hat bran ches to the indi vidual injectors, so it 's simi lar to a typica l port-ty pe gasoline EFJ albeit at up to 600 times the press ure. The injectors are opened when the CDI control unit sees fit, aga in si milar to EFI. As in any modern eng ine, the control unit gets signals from both crankshaft and camshaft posit ion sensors to determin e where the eng ine is in its four-stroke cycle (many oth er inputs are invol ved in the grand scheme of thin gs , too, of course), thus when to fire each injector, but it's relieved of the duty of cont rolling an ig nition system. The serious pressure in this system not onl y g reat ly enh ances fuel atomi za tion , it also makes th e effi cient direc t inject ion feature work better. Once diesel combustion ha s taken place and t he last possible ounce of power has been ex tracted fro m the air/ fuel charge, Mercedes-Benz made sure the ex haust comes out squeak y clean by mea ns of the Selecti ve Catalyst Reduction system (SC R) th at aids in th e continued co mbustion of any excess 14 Mercedes-Benz StarTuned It was 77 year s ago when Mercedes-Benz introduced the world's first diesel-powered passenger car, the 2600. fuel tha t did not burn i n the combust ion chamber. Thi s utili zes urea i njecti on -- a chem ical add it ive, commercially called Ad Blue® Diesel Exhaust Fluid (DEF), is sprayed i nto the SC R system. This type of system has been around for yea rs in t he Eu ropea n trucl<ing industry, so is not a new, unt ried concept. It's needed to make the engi ne emi ssionscompliant, and be full y functional in order for t he eng ine to be allowed to r un. An easil y-accessible Ad Blue® DEF tan k is mounted i n th e vehicle, and each gallon lasts at

least 2,500 m iles . A level sensor lets the control un it know how much flu id is i n the ta nk. lf the flu id drops below a specified level, a message w ill appea r in the i nst r ument cluster ("C heck Ad Blue® / Check Diesel Ex haust Flu id (DEF)"). I f t he veh icle is driven for a certai n amount of t i me with the wa rn i ng i ll umin ated, a gong w il l be sou nded. The number of gongs sounded starts at someth ing li ke 21, dependi ng on the model. If t he level is al lowed to drop even fu rther, the nu mber of gongs w i l l go dow n also reflec ti ng the nu mber of engi ne sta r ts permi tted. Once it reaches zero, the control un it wi ll either put t he engi ne into id le mode, or prevent it from sta rt i ng, dependi ng on the model. Add i ng a ga l lon of AdBlue® w ill get thi ngs going aga in . THE PLAYERS Here's what the ADBlue® DEF tank filler cap looks like. The fluid level is continuously monitored to make sure there is enough. When it gets low, a message will appear in the instrument cluster, then t here will be a warning gong. We al ready know the CDI control unit completes the ci rcuit to the fu el i njector s. We also lrn ow that the control unit rece ives cran k and ca m position sensor signals so it ca n determine when to fi re t he injec tors. But, as mentioned above, t here are many ot her sensors and solenoids that help ma nage al l that fue l press u re. Si nce t ime is of t he essence in Test of high-pressure regulation , Actual values . I""" 600 624 361 1338 -10s _j_ Os Rail pressure regulation : Rail pressure regulation Ilia press ure regulator vallle Pressure regul ator valve and quantity control valve (mixed-fuel operation) - - - ------- -- - - - ---- - -- - - - -- - - --- -- -- ---- - --- -- - -- - -- - - - ---- -- - - - --- - - - ------------~ Rail pres sure regulation Via quantrty control valve --- ---- -- ---- - - ------- - - - ---- ------ -- --- - --- ------ --- - - - - ----- - - - - ----- - -- -- ------~ Rarl pressure regul ation via pressure regulator valve With a XENTRY system you can graphically display the fuel rail pressure as picked up by the fuel rail high pressure sensor. Here, we see the thick black line indicating the increase in psi as the engine is cranked and started (then immediately shut off). This can help in the diag nosis of a no- or hard-start condition. December 2013 15

a high-pressure direct fuel inject ion system, more is needed t han just increased inj ector on-t i me to add enough fu el under acceleration. The pressure itsel f is increased in order to get more fu el into the combustion chamber under high demand. This is one in sta nce where diesel eng ines di ffer from their gasoline counterparts. With gasol i ne fuel i njection, injector pul se w idth is increased to meet the demands of acceleration, but system pressure stays pretty much con stant. COi controls t he amou nt of pressure in t he fuel system with a combination of a Quantity Cont rol valve (mounted on the high-pressure pu mp) and t he Pressure Control valve mou nted on t he fuel r ail. Both receive pulse-w idth modulated signals from the COi unit. The COi cont rol unit needs to be aware of the actual pressure i n the fuel rail (also ca l led a " mani fold ") i n ord er to ca lcu late pu lse w idth and pressure requ irements. Lt gets t his i nformation via a high-pressure sensor mounted on t he ra il. As w ith any other diesel, the high compress ion generated by the engi ne starts t he combust ion process. On ver y cold days, it is somet i mes difficult to get th e fire star ted. In older desig ns, there was a pre-cha mber w ith a glow plug installed. When the ig nition key was t urned on, the glow plug heat i ng element was suppl ied with electri c current. Th is wou Id heat t he fuel as it entered the chamber, maki ng it easier to ignite. Wit h COi, penci l-t ype glow plugs are mou nted directl y i nside the co mbusti on chamber for preheati ng. A separate glow plug cont rol un it supplies the necessa r y am perage wi th t he igni tion key on and duri ng the wa rm-up phase to i ncrease effi ciency. The glow pl ug control unit takes its orders f rom the CDI control unit. Here's th e fuel rail of th e new four-cylinder Mercedes-Benz diesel eng ine that 's gaining so much notoriety. Metal lin es car ry the pressur ized fuel to the individual injectors. The fuel volume is very small, so even a small leak will not allow pressure to build. This can lead to a hard- or no-start condition. 16 Mercedes-Benz Sta rTuned

INJECTION ACTUALITIES When we th in k of traditional gasol i ne EFI, we t hin k of a computer energizing a solenoid that allows pressurized gasoline to pass t hrough a nozz le. vVith a high-press ure diesel fu el system capable of produci ng 30,000 ps i or mor e, it may seem that it wou ld be virtuall y impossible to electrica ll y open an i nj ec tor whose pi ntle has t hat mu ch force bea rin g on it. Engineeri ng injectors that could do j ust that dependably was one of COi's break throughs. Depend ing on the year, model, and countr y of sa le, eit her t he Piezo type or electric soleno id ty pe has been used. Rega rdless, t he t raditional diesel's rattle and k nock are practica lly eli m inated by up to seven injection events occurri ng for each power st roke. It's not j ust one big blast any more, but a relati vely slow, con trol led burn . Bein g a seq uent iall y-fi r ed injec ti on system, CD I is prone to some of the sa me dr ivability issues usually associated w ith gasol i ne SEF I. Older diesel i njection systems ty pica ll y had a mechanical ly or electrically-cont rolled pum p. A rack inside t he i njection pump would be moved to provide more or less fuel to all of the cy linders. If you had an i ndi v idual cyli nder misfire, or " nailing," it was due to eit her the injector itself, or to an eng i ne mechan ica l problem, such as a bad va lve . With com mon-rai l, each cyli nder is i ndi v idual ly control led . CDI has the sensitivity to continuously mon itor and adj ust inj ector tlow rates to match the needs of i nd iv idual cylinders. The CDl unit needs to k now the flow rate of any injector t hat is bei ng replaced. T his in for mation is entered i nto t he CDI unit t hrough the SDS/XENTRY software. As the i njector wears, t he flow rate may change over t i me. The CDI uni t also monitors t hese cha nges and per for ms "adaptat ions" accordingly. These adaptatio ns need to be cleared after replaci ng i njec tors or otherw ise serv ici ng the system so the CDI does not inject fuel usi ng i n for mation from the old i njectors. These adaptations can be v iewed and reset wit h your SDS XENTRY system. / WE NEED FEEDBACK Just like modern gasol i ne i njecti on systems, t here needs to be a sensor tha t mon itors t he effectiveness of fu el contro l. The CDI un it is always ask i ng itself, "Am I inject ing too much or too little fuel for complete combu st ion?" To get an accurate answer to that quest ion, t he CDl unit uses a w ide-band oxygen sensor -- t he gasoline engi ne equiva lent would be cal led an ai1jfuel ratio sensor. These sensors have a si x-pi n connector and use a millia mp sig nal to indicate a r ich or lea n mi xture to the CDJ control unit. They ar e capable of measuring a wider r ange of m ix t ure ratios th an cou ld a traditional zirconium oxygen sensor. Hav i ng a good understand i ng of modern Mercedes-Benz diesel fu el i njecti on systems wi ll allow you to perform proper maintenance and more acc urate diagnosis of any complai nts. Your local Mercedes-Benz deale r 's pa r ts depart ment is a part ner i n this process, and w ill support you in mak in g sure you have t he k nowledge and t he qua l it y parts needed to se rve your customers in t he most profess iona l manner possible. I Left: Between the fuel pump and the high-pressure pump, there is a fuel filter with a "water in fuel" sensor. When the filter's water separator is more than half full of H20, a warning light in the cluster will turn on. This filter needs to be replaced at the specific intervals outlined in the maintenance booklet, but may need to be replaced more often depending on the quality of the diesel fuel available to your customers. December 2013 17

Reman Airmatic Strut MSRP* New MSRP* % Savings A219 320 1113 80 $1,140.00 $928.00 -19% A219 320 1213 80 $ 1,140.00 $928.00 -19% A211 490 0819 80 $1,720.00 $890.00 -48% A211 490 0919 80 $ 1,180.00 $581.00 -51 %

A642 010 4006 80 S3 0 ,170.00 $ 13,830.00 Genuine Mercedes-Benz Reman Parts: Value, Quality and Reliability All Genuine Mercedes-Benz Remanufactured parts are renewed and produced to the exact Mercedes-Benz specifications, ensuring optimal performance at significant savings. ~ - Cl~ Ou••.&G..10) ~ Mercedes-Benz G Remanufactured p rt For the complete portfolio of Remanufactured products, please contact your authorized Mercedes-Benz Dealer or visit . enwne ll~IDiL @ Mercedes-Benz •Excludes core charge.

Let's just hit thi s head-on: In spite of w hat some snide automoti ve journa l ists have said comparing the Amer ican i ntroduction of a Mercedes-Benz FWD platform to "the fall of Western Civ ili zat ion," or "the end of life as we know it," it is anyt hin g but. Instead, it represents an i mportant, positi ve departure t hat w i ll allow the St uttga r t company to weather the pred ictecl tu rm oi I of extreme fuel economy ancl emissions regulat ions, ancl , w ith it 's high-value pricing, attract anoth er whole level of buyers to the brand , whi ch ca n' t do any thing but help Mercedes-Ben z ser v ice special ists l i ke you. The FW D CLA belongs to the company's "New Generation Compact Ca rs" fami ly, whi ch w ill go a long way i n defining its futu re, here and elsewhere. The Model Seri es 117 is a fou r-cloor premium coupe in th e compact segment, bu i lt on the current A-Class and B-C lass moclels solcl elsew here. Innovations abound in thi s class that i mprove energy efficienc y ancl further reduces emissions, besides offering unprecedented safety ancl comfor t in a car at thi s price point. Wh ile you probabl y won' t be seeing these cars in you r bays for some yea rs, we at StarTunecl bel ieve you shoulcl have a clear iclea of w hat your future holds, so here we're going to lay out the amazi ng array of features the CLA presents (well , ma ny of the important ones, at least). FOUR -- WHO NEEDS MORE? The AMC CLA 45 versi on , at $ 17,550 more than the CLA 25 0, is bil lecl as hav ing the most powerful production fou r-cyl i nder in the world w ith 355 hp ancl 332 ft. lbs of twist. But you'll be seeing a lot more of the CLA 250, which is no slouch. With 208 hp and 258 ft. lbs. of torque, it produces a nice combin ation of 0-60 in less than seven seconds, along with 26 city/38 hi ghway mpg -- incredible for a 2L in a 3,300 lb. car. Th is feat is achieved by means of the fol lowi ng engine character istics (among other thin gs): • Low i nterna l fr iction • Gasol ine direct injection • Piezo injectors for multiple fuel injection events • Tw in-pipe/ scroll turbochargin g w ith up to 27 psi (1.8 bar) of boost • Highl y-evolvecl intake ancl ex haust cam shaft dy namic t i ming adj ustment • Dem and-controllecl multi-spark ig nition • Opt i mi zed thermal management • ECO star tjstop function •Opt i mi zed regulation of the oil and cooling ci rcuit pumps DRAG & MULTI-SQUIRT & SPARK Mercedes-Benz was the first automaker to use cast-in si licon-alu minum cylinder sleeves w ith a low-friction surface that allows piston-rin g spr ing tension to be reduced by 50 perce nt. In the CLA's case, t he cyl inder sleeves get a "NANOSLIDE" coating to optim i ze both the production process and friction characteri stics. Other mechan ica l eng ine features include forged pistons des igned to w it hstand ign it ion pressure loads of 2, 100 psi (140 bar), a forged cra nk shaft w ith eight coun ter weights, bearing caps made of cast iron with nodu lar graphite, and a v iscous vibration cl amper. Don't be shocked to see that four-cylinder engin e in there transversely. It 's an essential element of Mercedes-Benz's "New Generation Compact Cars" fam ily. Shown is an A-Class, which has been successful in other markets. Another first for the company was the ori gin al gasol i ne direct inj ect ion system on the legendar y 1 954 300S L Gull w i ng. The t hi rd generation of modern GDI uses piezo-cerami c cr ys talline elements i n the inj ectors. Replacin g mechanical solenoids, the piezo cr ys tal changes shape December 2013 21

in stantl y when electrical current is applied, wh ich makes it possible to progra m several small injection events per cycle. The first occurs as t he piston is descending on the intake stroke. Depend i ng on speed , load, and temperature conditions, another i njection (or two) takes place durin g the compression stroke before ignition, for mi ng a strati fi ed m ix ture. A fourth inj ection can stabili ze combustion if it's needed. System pressure, by the way, is up to 2,840 psi (190 bar), i n the range of a pre-common ra il diesel. • Electronic accelerator • ECO startjstop function • Stepless adjustment of i ntake and exhaust ca mshaft tim i ng • Turbo boost pressure • Torque i nterface to ESP, tra nsmi ssion, and air condition i ng • Alternator i nterface Coord i nated w ith th at sophisticated meteri ng of gasoline is mu lti-spark ignition. After the first spark, the syste m ca n recha rge and deliver up to three more sparks w ithin a single millisecond, creatin g a gas plasma w ith more expansion than convent iona l ignition wou ld allow. The ti me lapse between spark s is adjustable, so combustion duration ca n actuall y be controlled, r esulting i n two percent better fuel economy, and a tota l of four percent improvement in combination wi t h di rect fuel injection. Of course, t hese prec ise fu nctions are orchestrated by t he M E-S FI control un it, wh ich is attached to the ai r Fi lter housing for cool ing. It does a lot more than that, t hough, i ncluding management of: • Cyli nder-selecti ve, adaptive knock control 22 Mercedes-Benz StarTuned Here's the mighty AMG version of the CLA 2L engine. At 355 hp and 332 ft. lbs. of torque, it's the most powerful production four-cylinder in the world.

• Thermal management for shortening warm-u p phase • Engine oi l pum p control • Ex hau st fl ap control • Diagnosis and fault storage • Drive authori zation system and immobili zer If the M E detects a mechanical fault i n the electronic accelerator throttle actuator, the fu el i njectors are partia lly shut off in order to restr ict engi ne speed to 1400 r pm at idle, and 1800 r pm whi le dri vi ng. Ano ther safety-r elated job is shutting dow n t he fu el pump in the absence of an engine speed signal, or if a crash signal is received indirect ly v ia the chassis CA , or direct ly from t he supplemental rest ra i nt system control uni t. In addition , t he injectors are briefl y actuated to depr ess u r ize t he fu el system. CURRENT MANAGEMENT The electrical system batter y (GI) is located in the driver 's side of the engine compartment. A n add itional batter y (G l/ 13) for the ECO star t;s top fun ct ion is i nsta lled in the front passenger footwell. The bottom end looks indestructible. The crank, rods, and pistons are all forged. The energy managem ent system ensu res that the engine can be started and that al l electrica l consumers receive a reli able power suppl y. Th is is ach ieved th rou gh the major assembly coordinator and on-board electrical system management subsystems. The major assemb ly coordinator is A low-pressure pump moves gasoline from the 50L high-density polyethy lene tank (six layers with a block layer made of ethylene vinyl alcohol to prevent hydrocarbon evaporation) to the high-pressure pump, which can generate an impressive 2,840 psi (190 bar). December 2013 23

for usage with the startjstop func tion. When thi s function is acti ve (engine off), the electric auxiliary oil pump supplies the shift elements and actuator s w ith oil. integrated into the ME and forms the interface of the on-board electrical system management to the alternator. T he ME communica tes with the altern ator v ia the powertra in LIN (LI N C1). The major assembly coord inator regu Iates the power output of the alternator i n accordance with the instructions of the on-board electrica l system management, taking engi ne load into account. Automatica ll y controlled all-w heel drive (4M AT IC) is optional, w ith power sent to a mu ltidisk clu tch i n t he rear ax le differential. ELECTRICALLY-POWERED STEERING Yet another big advance is the electric power steerin g, wh ich consists of a rack-a nd-pi nion steeri ng gear, a torque sensor, an actuator motor, and a control unit. The steering assista nce is transm itted The on-boa rd electrical system diagnosis function provides precise analysis of causes i n the event of complaints. The last 100 dri vi ng and idle cycles are stored with im portant in form ation. Th is can be read out using Xentry. In addition, the diagnosis function now makes it possible to r ead the no-load cu rrent curve for the most recent hours and display it graph ica lly. The lG-DCT transaxle is a sevenspeed, dual-clutch, three-shaft unit. Clutching and gear changes are rapid with no rpm flare. TRANS The adoption of FWD and the ti ghtened requirements for performance and fuel efficiency r esulted in a trul y unique new transax le. The 7G-DCT is a 7-speed dual-clutch, three-shaft transmi ssion unit. It consists of two subtransmissions each w ith its own clutch. Clutch operation and gear changes occur rapidly w ithout interruption of tractive power for improved effi ciency and sport y vehicle dynamics. A few more important features of t he 7G-DCT: • Wet, hydrau lica l ly-operated dual clutches • One oil circuit for hydraul ic control and lubrication of the gear set • Integrated electric aux iliary oil pump • Integr ated shiftby-w i re Cooling is hand led by an ac ti ve oil system. It is also suitable 24 Mercedes-Benz StarTuned At a Glance ... MSRP Fuel Economy Engine Performance 0-60 (sec.) CLA250 $29,900 City: 26MPG Highway: 38MPG Combined: 30MPG CLA 250 4MATIC $3 1,900 TBA 2.0L lnline 4-Cylinder Turbocharged 208 HP 258 lb-ft torqu 2.0L lnline 4-Cylinder Turbocharged 208 HP 258 lb-ft torque 6.9 6.8 (est.)

by the motor to the rack-and-pinion to boost the steering moment applied by the dri ver. Compared to hydraulic power steering, electric steering force assistance offers the follow ing advan tages: • Electron ic brake fo rce distribution (EBD) • Anti-lock braking system (ABS) • Acceleration skid control (ASR), electronic traction system (ETS) •Im proved steering feel • Brake Ass ist (BAS) • Fuel sav ings • Dry braki ng • No power steerin g fluid req uired • Compact design • Precha rg i ng, depending on acceler ator pedal actuation • Speed-dependent steering force assistance • Prechargin g, depend ing on lateral acceleration • Ass isted steerin g return • Standstill coordinator (SSK) •Diagnosis capabil ity • System fault d isplay The brake and engi ne intervent ion function s of ESP, which are intended to stabi li ze the vehicle, have been supplemented by steeri ng torque intervention. This additional steerin g torqu e is prov ided in the form of electri c steerin g force assistance. TONS OF BRAKE FEATURES Mercedes-Benz has spared no effort to make su re the CLA has an i ntegrated bra ke system that's more than a match fo r the compet ition where high-technology is concern ed. For exa mple, ABR (Adaptive Brak e) assists the driver in da ngerous situation s which occur suddenly. Th e fa mili ar system has been adapted to t he new model ser ies and consists of the fo llow ing subfuncti ons: • ESP dynam ic cornering assistant There's even a n electric par king brake, wh ich is identical to t hat fou nd on models R231 (SL) and R172 (SLK). It acts on the rear w heels by makin g use of spec ial elect r ically-adapted brake ca lipers, w hich ar e oper ated via a sw itch on the in strument panel. As you can see, t here's way too much new technology in the CLA for us to be able to delve very deeply into it in one magazine article, but we w ill concentrate on the operation and d iagnosis of spec ific systems in future issues of StarTuned. I • Electronic Stability Program (ESP) 4MATIC is a great option. The rear axle carries a multidisc clutch, and up to 50% of the engine's torque can be directed to the rear axle. This may look like terra incognita to you -- FWD, MacPherson struts, and electrically-powered steering -- but it's thoroughly modern and wor ks superbly. Note the long link between the stabilizer bar and the strut. December 2013 25

Mercedes-Benz Mobil 1 Part Number Quantity BQ 1090144 Bulk - No Equipment BQ 1090162 6/ 1 Quart Cases BQ 1090151 Product Name Product Description Recommended Consumer Applications Fully synthetic formulas designed specifically for gasoline passenger cars 55 Gallon Drum Low SPAsh. Available at most MB dealers Fully Synthetic formula specifically designed for Mercedes-Benz engines that require the 229.5 Specification . . ~ngm~s that require 229 · 5 Specification Oil Fully synthetic formulation designed to meet the requirements of many European vehicles Porsche A40. Many European vehicles. HT/TS applications. Advanced full synthetic formulas designed specifically for diesel passenger cars that have particulate filters Low SPAsh. Available at most MB dealers Higher viscosity, advanced full synthetic formula designed for performance vehicles Porsche A40. HT /HS applications. Mercedes-Benz SPEC. Mobil 1 Formula M 5W-40 Genuine Mercedes-Benz Oil MB 229.5 Specification SAE 5W-30 A0009898301 USA6 12x1 Quart Cases A0009898301 USAB 55 Gallon Drum A0009898301 USA9 Bulk - No Equipment BO 1 090010 Bulk - No Equipment BO 1 09 0015 6/1 Quart Cases BO 1090016 55 Gallon Drum BO 1090135 Bulk - No Equipment BO 1 090142 6/ 1 Quart Cases BO 1090143 55 Gallon Drum BQ 1 09 0133 16 Gallon Keg BO 1090134 6/1 Quart Cases Mobil ATF 134 BO 1 09 0166 55 Gallon Drum Extra high performance automatic transmission fluid formulated with selected HVI base oils Recommended for use in Mercedes-Benz automatic gearboxes Mobil 1 ESP Formula MB 5W-30 BO 1 09 0165 12x 1 Liter Cases Advanced full synthetic formulas designed specifically for passenger car diesels that have particulate filters Low SPAsh. Available at most MB dealers. AdBlue"' 1/2 Gal. A 000 583 0107 1/2 Gallon Bottle Diesel Exhaust Fluid 55 Gal BO 1470002 55 Gallon Drum BO 1 09 0017 6/ 1 Quart Cases BQ 1 09 0018 55 Gallon Drum BO 1090019 6/1 Quart Cases BO 1 09 0020 16 Gallon Keg BO 1 09 0021 55 Gallon Drum BQ 1 09 0083 6/1 Quart Cases BO 1 09 0084 55 Gallon Drum BO 1090169 6/ 1 Quart Cases BO 1 090168 55 Gallon Drum BQ 1090174 6/ 1 Quart Cases BQ 1 090164 6/ 1 Quart Cases BQ 1 09 0163 55 Gallon Drum BO 1090023 BO 1090085 Mobil 1 OW-40 Mobil 1 ESP Formula M 5W-40 Mobil 1 5W-50 Mobil 1 5W-30 Mobil 1 lOW-30 Mobil 1 15W-50 I Mobil 1 Gear Oil (Mobil 1 Gear Lube 75W-90) I Vehicles that require 5W-30. Corvette approved. Vehicles that require 5W-30 or lOW-30 Most vehicles that specify OW-20 (newer Toyotas and Hondas), 5W-20 and certain hybrids Advanced full synthetic formulation designed for enhanced fuel economy and cold weather performance Most vehicles that specify 5W-30 or l OW-30 Multi-vehicle, fully synthetic fluid designed to meet the demanding requirements of modern passenger vehicles Vehicles that require Dexron Ill, Ford Mercon and Mercon V performance levels 55 Gallon Drum Boosted, higher viscosity, advanced full synthetic formula designed for performance vehicles HT/HS applications. Racing and Flat tappet applications 12/1 Quart Cases Exceeds the most severe service requirements in both conventional and limited slip applications SUITABLE for use in modern high performance automobiles like SUV's, Vans and Light duty trucks requiring API GL-5 level performance Mobil 1 OW-20 AFE Mobil 1 Synthetic ATF Advanced full synthetic formula designed for domestics and imports Recommended for use in MercedesBenz, Volkswagen + BMW AdBlue"' (DEF) applications vanced u I synt et1c ormulat1on designed to meet the requirements of many newer vehicles including Hondas, Eatds Cbt)lslets aad aewet Ia)latas Advanced full synthetic formulation designed for enhanced fuel economy and cold weather performance Mobil 1 5W-20 Mobil 1 OW-30 AFE Non-toxic solution that transforms harmful Nitrogen Oxide (NOx) emissions from diesel-powered vehicles into harmless water vapor and nitrogen Advanced full synthetic formulation designed to meet the requirements of many domestic, including GM, and im orted vehicles Vehicles that require 5W-20

M ercedes-Ben z automobi les are designed to perform on the most challenging roads and conditions. Shouldn't the oil used in Mercedes-Benz engines do the same? We think so. Th at's why Mercedes-Benz and Mobil I have partnered ro offer an unbeatable combination of total eng ine performance and driving luxury. Please have a look at our oil portfolio which is available through your local Mercedes-Benz dealer. Our dealers are able to offer you a w ide variety of oil grades at competiti ve prices. Product Name Part Number Quantity Product Description Recommended Consumer A llcatlons BQ 1090085 12/ 1 Quart Cases Exceeds the most severe service requirements in both conventional and limited slip applications SUITABLE for use in modern high performance automobiles like SUV's, Vans and Light duty trucks requiring API GL-5 level performance BQ 1 09 002464 Bulk - No Equipment BQ 1 09 0171 12/1 Quart Cases BQ 1 09 003064 55 Gallon Drum Formulated from quality base stocks combined with modern performance additives to give the engine the expected protection and performance under a wide variety of operating conditions Recommended for gasoline fueled automobiles and light duty trucks requiring an API SN/SM/SL/ SJ BQ 1 09 003164 Bulk - No Equipment BQ 1090172 12/ 1 Quart Cases BQ 1 09 003764 55 Gallon Drum Formulated from quality base stocks combined with modern performance additives to give the engine the expected protection and performance under a wide variety of operating conditions Recommended for gasoline fueled automobiles and light duty trucks requiring an API SN/SM/SL/SJ BQ 1 09 003864 Bulk - No Equipment BQ 1090173 12/ 1 Quart Cases BQ 1 09 004464 55 Gallon Drum Formulated from quality base stocks combined with modern performance additives to give the engine the expected protection and performance under a wide variety of operating conditions Recommended for gasoline fueled automobiles and light duty trucks where a higher viscosity API SN/SMSL/SJ oil is preferred or recommended BQ 1 09 012464 Bulk - No Equipment BQ 1 09 0170 12/ 1 Quart Cases BQ 1 09 013264 55 Gallon Drum Formulated from quality base stocks combined with modern performance additives to give the engine the expected protection and performance under a wide variety of operating conditions Recommended for gasoline fueled automobiles and light duty trucks requiring an API SN/SM/SL/SJ Formulated from quality base stocks combined with modern performance additives to give the engine the expected protection and performance under a wide variety of operating conditions Recommended for gasoline fueled automobiles and light duty trucks where a higher viscosity API SN/SMSL/SJ oil is preferred or recommended Extra high performance diesel engine oils that help extend engine life in the most severe on and off-highway applications while delivering outstanding performance in modern, high-output, low-emission engines including those with Exhaust Gas Recirculation (EGR) and Aftertreatment Systems with Diesel Particulate Filters (DPFs) and Diesel Oxidation Catalysts (DOCs) Specifically recommended for the latest low-emissions, high performance diesel applications equipped with aftertreatment systems using Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC) technologies Fully synthetic supreme performance heavy duty diesel engine oil that helps extend engine life while providing long drain capability and fuel economy for modern diesel engines operating in severe applications Recommended for use in all super high performance diesel applications, including modern low emission engine designs with Exhaust Gas Recirculation (EGR) Formulated to provide excellent high temperature performance with superb adhesion, structural stability and resistance to water contamination Recommended for industrial and marine applications, chassis components and farm equipment Extra high performance, automotive lubricant formulated from select base oils and an advanced additive system specifically for limited-slip differentials Recommended for use in limited-slip differentials, axles, and final drives requiring API GL-5 level performance Mercedes-Benz SPEC. Mobil 1 Gear Oil (Mobil 1 Gear Lube 75W-90) Mobil Special 5W-30 Mobil Special lOW-30 Mobil Special l OW-40 Mobil Special 5W-20 Mobil Delvac 1 5W40 Bulk - No Equipment BQ 1 09 0058 12/ 1 Quart Cases BQ 1 09 0059 4/1 Gallon Cases 55 Gallon Drum BQ 1 09 0086 Bulk - No Equipment BQ 1 09 0051 Mobil Delvac 1300 Super 10W30 55 Gallon Drum BQ 1 09 0060 Mobil Delvac 1300 Super 15W40 BQ 1 09 004664 BQ 1 09 0053 Mobil Special 20W-50 4/ 1 Gallon Cases 60 / 14 oz Cartridge BQ 1 09 0079 120 lb Keg BQ 1 09 0080 400 lb Drum BQ 1 09 0098 40/14 oz Cartridge BQ 1 09 0096 Mobil Lube HD Plus 80W90 55 Gallon Drum BQ 1 09 0078 Mobil Grease XHP 222 BQ 1 09 0052 120 lb Keg BQ 1 09 0097 400 lb Drum

r FWD & MacPherson Struts Change the Collision Repair Game Many advanced steering, stability control, and propulsion technologies in the front-drive CLA depend upon precise suspension geometry for proper vehicle operation. Here are some front wheel drive suspension basics for collision repairers who will be working on this history-making model.

If y ou work exclusively on Mercedes-Benz vehicles, this will be new to you. Of particular importance in collision repair are the position of the cradle, and differences in suspension alignment set tings. Note the long stabilizer bar links. For the youn g, upsca le market th at the CLA 250 is i ntended to att ract, it offers lux ury, a ton of advanced technology and sa fet y features, and aggressive design cues, all at a new, compet it ionbusting price poi nt. Technicians - i f you cut your coll ision repa ir teeth on Mercedes-Benz rear wheel drive vehicles, read on because FW D and MacPherson stru t front suspension mean there are some new things to take i nto consideration. The suspension of this front w heel dr ive model is tasked wi th controll ing veh icula r movement under a vari ety of speeds, weight loads, road condit ions, and driver intentions. This routinely requ i res resisting or red i rec t i ng t he k i net ic energy of a 3,300 lb. vehicle t hat is in a consta nt ly changi ng state of motion. THAT NEWTON GUY Newton's First Law says t hat a body in mot ion will continue t hat motion u nti l it is acted upon by an opposing force. Just to make l ife fun , Newton's Second Law says t hat there is always an opposi ng force, and it w ill generally eq ual t he other. Think about a veh icle about to enter a turn. The inertial force established by t he vehicle's speed, weight, and ba lance wa nts to pu sh st raight 30 Mercedes-Benz StarTuned ahead . As the driver t u rns the steer i ng w heel, the cornerin g forces of t he ti res act against t he mom entum of the vehicle to change its di rection. Newton's First, meet Newton's Second. A LITTLE PATCH WILL HOLD US A ll of the forces t hat cont ribute to di rectional control, corn eri ng abi l ity, vehicle stabi l ity, velocit y or t hrust, and r ide comfort mu st accomplish thei r goa ls t hrough the small patch of t i re t read t hat is actua ll y i n contact with the road at any one t i me. The job of t he suspension is to turn, t i lt, and pos ition t he wheels so t hat little patch of tread maxim izes its gri p on t he road i n spite of all of the di fferen t forces at play. SECONDARY DAMAGE Collision energy can travel t h rough t he veh icle to other areas that may be on ly indirectly related to t he point of impact, w here it can cause seconda r y, or h idden, damage. Secondar y damage may be di fficu lt to catch wit h a trad it ional visual inspect ion. If you miss a bent strut or control arm , the ti re patch won't hold the road properl y, and your fi nished repai r wi ll come back from the al ignment bay need ing add it ional work.

The position of the strut towers is particularly important. Any deviation due to collision damage will have a big effect on caster (not adjustable), camber, and vehicle dynamics. If you want to avoid an unpleasa nt 5 o'clock surprise (most likely not included on t he original estimate), you must search for secondary damage. Check for loose or worn ball joi nts, lea kin g or bent struts, and damage to upper strut mou nts and lower control ar ms, tie rods, and other key components. Measure the distance between reference points ("VB, " not to be confused with a type of engine the CLA doesn 't have) at each front strut tower. If there is a problem with a strut itself, MercedesBenz recommends replacing only th e damaged side, not both struts. Since you are probably used to workin g on rear w heel dri ve wit h upper and lower cont rol arm s or w ishbones, you should rea lize that it's i mportant to spend a little ex tra time maki ng sure that stru t tower placement and cradl e alig nment match OE speci fi cat ions. In its Work shop Informat ion System (WIS), Mercedes-Benz recom mends tak i ng a series of measu rements to check for bent fro nt suspension components and mounti ng poi nts. The l ist of measure ments includes, but is not l imited to, t he distance between t he front bea rings of t he front ax le carrier, between t he rear outer mounts of the fro nt ax le carrier, between t he front bea r i ng of the front ax le and the rea r outer mount of the front ax le carrier, a nd the distance bet ween suspension st rut towers. THREE ANGLES, PLUS . . . The big three suspension ang les to check on an FVVD vehicle are the sa me as fo r a RWD -- cas ter, December 2013 31

camber, and toe -- but there are some subtle differences. We'll go through the basics here to make it easier to see them. Caster refers to t he til t of the steeri ng ax is when viewed from the side of the vehicle. The steering axis is a line drawn through the upper and lower steering pivot points. On t raditional MercedesBenz vehicles, these would be t he upper and lower ball j oints in t he control arm s. With the strut system i n t he CLA 250, on the other hand, t he upper pivot is the center of the strut's top bearing mount and the lower pivot is the lower ball joint. Regard less, positive caster til ts the top pivot towa rd the rea r of the vehicle. When an i magi nary l ine through the steering ax is meets t he ground at a point ahead of the center point of the tire contact area, it cr eates a sel f-centeri ng force that helps keep the wheels pointed straight. Th is is responsible for pu 11 i ng a vehicle back to the straight-ahead position w hen the driver lets go of the steerin g wheel while coming out of a turn. Since the top strut mounting position on the CLA 250 is fixed, caster ca nnot be adjusted. Large deviations in specified caster may be due to a bent lower control arm, damaged or misa ligned front ax le carrier, or body damage that affects the position of the upper strut mount. A fter mak in g the appropriate collision repa irs, compare caster measurements on the vehicle aga in st speci fications in WIS to confirm that you have corrected the problem. CAMBER Ca mber is the inward or outward ti lt of the top of the wheel when viewed from the front or rea r of the vehicle. Measured in degrees, an i nward tilt is said to be negati ve, and an outward til t positive. Proper camber helps position the wheel so th at it contacts the road with as even an amount of force as possible across the width of the tire as th e spring compresses and rebounds. This minimi zes uneven tread wear, and, more i mportantly, helps keep the vehicle rolling st raight dow n the road. 32 Mercedes-Benz StarTuned A difference in camber angle that exceeds 1/2 a degree side-to-side wi ll cause t he vehicle to pull to the side with the higher camber. In other words, a vehicle wi ll pull toward the side w ith the most positive camber, all other th ings bei ng eq ual. Possible causes of camber t hat does not match specifications include a bent spind le, strut, or control arm, or collision damage that has shi fted an upper strut mount to one side (the first th ing to measure is the distance between the strut towers). For safet y reasons, NEVER try to st raighten any suspension components, such as struts or control arms. If bent, they must be replaced. Front suspension camber is adjustable on the CLA. Check in W IS for the exact settings to achieve the desired front axle camber. TOE IN OR OUT? Toe is simply a comparison of the distance between the leadi ng and trailing edges of the front or rear pa ir of tires. If the lead ing edges are closer together than the trai lin g edges, ali gnment is sa id to be " toed-in," and vice versa. To adjust camber on the CLA 250, loosen the nuts (1b) that attach the strut to the steering knuckle. Use a wedge between the strut tube and the wheel rim to force the rim outward to achieve a more positive setting, and to hold the setting in place. Once you've got camber where you want it, tighten the upper nut first, then the lower nut, and re-check the setting. Torque the nuts to 110 Nm, then twist an additional 90 deg.

Here's where RWD and FWD differ. With RWD, as the vehicle is being powered dow n the road, t read drag tends to push the leading edges apart. This force is obviously not present while you are making the adjustment, so the specification will typically be toed in slightly to compensate for dynam ics. With FWD, the front wheels are pulling the vehicle forward whenever engine power is applied to t hem, wh ich wou ld tend to force the lead ing edges of the tires together. So, you mi ght ex pect that the specification would be toed out. That doesn' t take into account coasti ng, however, during wh ich mode the forces would be the same as t hose of a RWD vehicle. A lways check WI S for the specified settin g, wh ich represents a proper compromise. Mercedes-Ben z engineered in less than 1/4 of a degree of toe-in. Permissible difference in toe between the right and left sides of the front ax le is ±0° 1O'. Toe settings have a major impact on tire wear. Excessive toe-in or out causes tires to scrub against the road surface even w hen dri vin g straight. If toe is off by 1/ 8 in. (3mm), each tire on that axle w ill scrub the road sideways 28 feet for ever y mile traveled. Too much toe-in accelerates outer tread wear, w hile excess toe- out causes rapid wear of the inside tire edge. The front axle toe specification for the CLA 250 is 0° 1 (±10'). With the steering wheel and steering 2' gear locked in center position, hold the tie rod (10) and loosen the jam nut (10f). Rotate the tie rods to adjust the toe angle (see WIS for rear toe specifications and adjustment instructions). Normal wear to the tie rod ends and other steering linkage parts, in add ition to col I ision damage, ca n cause toe to become out of compliance w ith the carefull y-consider ed OE specification s. A ny other toe setting w ill produce the scrubbin g that eventuall y causes a feath ered or sawtoot h wear pattern on t he tire. Check for feathered or sharp edges by rubbing your hand lightl y across the tread. If it fee ls smooth when you move your hand toward the center of the vehicle but rough when you reverse hand movement toward the outside, the cause is excessive toe-in. Sha rp edges wi ll point in the opposite direction if t he problem is excessive toe-out. THRUST ANGLE If the steering wheel is not centered while the vehicle's wheels are moving straight, or the body appears to be movi ng at an angle ("dog tracki ng"), you have a thrust angle problem. The first steps in correcting th is problem include ensuri ng that sideto-side speci fications are met, and replacin g damaged tie rods, control arms or other rear suspension components. You can adjust rear toe to the vehicle centerline as part of a fou r-wheel alignment. RIDE HEIGHT & SAi If ride height is unequal by as little as 1/8" (3mm) side-to-side, it ca n negati vely affect both toe and ca mber. Sagg ing, bent, or broken spri ngs Toe is adjustable in the CLA 's double wishbone independent rear suspension using the cam bolts (60a). If cam bolt repositioning does not bring rear toe into specification per WIS, replace the tie rod (60). December 2013 33

can ch ange the vehicle ride height and ther efore alter the suspension angles. You can no longer jud ge whether or not ride height is in balance by how hi gh the fender edge on each side comes up your leg. Mercedes-Benz measures the vehicle level side-to-side difference in degrees, and speci fie s that t here ca n be no more than ±1.3° difference between the ri ght and left sides at the CLA front ax le. Keeping the ti re patch in the ri ght place wou Id be relati vely easy if road s were perfect ly smooth and had no turns. Since that is not the case in the rea l world, we have Steering Ax is Inclination (SA I). This is accompli shed by hav ing the spindle attached to the ax le at an angle t hat moves the swivel line downward from the top position, thus enlisting gravity to help keep the wheels in the straight-ahead position and to significantly reduce t he steerin

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