Published on November 6, 2007
Fuel Systems: Fuel Systems Fuel tank: Fuel tank Constructed of steel or plastic Most have baffles or surge plates Internal expansion areas Prevents fuel from getting into vents Prevents explosion of tanks Liquid vapor separators Roll over valves Fuel tank service: Fuel tank service Sender R&R using brass drift or special tool Repairs should be done by radiator shops Fuel caps: Fuel caps Important seal of vapors - hydrocarbons Must be tightened to three clicks Usually allows air in freely but only out if greater than 1-2psi Remove when doing other repairs that require opening of fuel lines Fuel lines: Fuel lines Pressure relief before opening fuel lines Usually have both feed and return lines Return line to keep fuel cool and prevent vapor locking Lines can be steel, rubber or nylon Nylon will kink and is not repairable DO NOT PINCH OFF Fuel line fittings: Fuel line fittings Low pressure fuel systems usually use a tapered seat High pressure fuel systems usually use an oring Viton orings vs. regular rubber orings Nylon lines usually use quick disconnects Filters: Filters Usually two filters in systems Main filter usually pleated paper Can be located in carburetor Screen type filter - poor filtering Strainer or sock in tank Mechanical fuel pumps: Mechanical fuel pumps Normally low pressure systems Runs off of an eccentric Can run with a pushrod off of eccentric Will have inlet and outlet check valves Mechanical pump failures: Mechanical pump failures Diaphram failures Leaks from weep holes or into oil diluting it Broken springs creates a knocking pump Worn eccentric Mechanical pump symptoms: Mechanical pump symptoms Lack of power on carburetor cars (after float bowl empties) Often plugged fuel filter Mechanical pump pressure testing: Mechanical pump pressure testing Use vacuum / pressure gauges Typically 3-5 psi Strong pulsing gauge indicates check valve problems Mechanical pump volume testing: Mechanical pump volume testing Most important test related to output 1 pint in 30 seconds Plugged fuel filters will cause low volume but not low pressure Electric pumps: Electric pumps Most common type is rotary vane Usually incorporates pressure relief valves Can be mounted anywhere but usually in tank Easier to push fuel than to pull it Submerged to keep cool Usually uses fuel to lubricate pump Electrical pump failures: Electrical pump failures Common to bind up and drop output Common to open with worn brushes Common to seize up Electrical pump symptoms: Electrical pump symptoms Lack of power on fuel injected vehicles instantly at WOT Often plugged fuel filter Can create no starts Electrical pump testing: Electrical pump testing Use fuel pressure gauges - must tee into line Typically 10-20 psi for throttle body Typically 30-50 psi for port fuel Pressure testing under load is best volume indicator Plugged fuel filters will cause low volume but not low pressure Dead head testing - pinch off return line - actuates relief valve Fuel pressure controls / pressure regulator: Fuel pressure controls / pressure regulator Located after injectors More volume dumped off at idle than at WOT Some use vacuum Primarily to compensate for vacuum acting on injector pintle Returnless systems: Returnless systems Some manufactures are now putting regulators in the tank No return line needed - it is in the tank Fuel pressure regulator failures: Fuel pressure regulator failures Can stick can excessive pressure to bleed off Diaphram can rupture Fuel pressure regulator testing: Fuel pressure regulator testing Monitor pressures Pinch off return line will determine if regulating Pull of vacuum line to inspect for rupture Electric pump controls: Electric pump controls Must not run pump if in accident Relay operation / prime pulse Inertia switch found on Fords Controls of pump relay: Controls of pump relay Computer based on rpm Charging system Oil pressure Air flow contacts Oil pressure bypass
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