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For more information about fuel pumps theory, improving fuel pumps accuracy, and calibration techniques, see the
Swisor Auto Parts Technical Reference Manual.

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Reference Manual



Reference Section--Fuel Tank Removal

1.Make sure the vehicle has some fuel in the tank. If in doubt, add a few gallons and again try starting the vehicle before proceeding.
2.Check the vehicle's on-board diagnostic system for any fault codes. These should be corrected before diagnosing the fuel system.
3.Using a wiring diagram and voltmeter, check specific voltage at pump relay, fuse, inertia switch. oil-pressure switch and engine-control module.
4.If the pump is receiving the correct voltage, turn key on. Pump should start and run from two to four seconds.
5.If the vehicle runs, but is hard to start, install a pressure gauge by teeing into the fuel line (TBI) or using the service fitting on the fuel rail (EFI). Turn the key on and check the gauge to make sure that the pressure does not drop more than 10% of its maximum reading. If adequate pressure is not maintained, the check-valve is stuck. Replace the fuel-pump assembly.
6.Start the vehicle and check fuel-system pressure with the gauge still hooked up. If system pressure is too high, it may indicate a defective pressure regulator, a kinked or broken vacuum line, or a blocked return line.
7.If the fuel-system pressure is too low, it may indicate a leaking pressure regulator, a clogged fuel-pickup strainer, or a blocked fuel-line filter.
Removing the Fuel Tank
When the in-tank fuel pump is identified as the problem component, the fuel tank must be removed or lowered enough for access to the pump hanger assembly. (Refer to vehicle repair manual.)
Before servicing, please review the safety precautions 1 and prepare the work area for the cleanliness requirements.
1.First, release tank pressure by removing the filler cap. Then relieve fuel system pressure by removing the pump fuse and running the engine until it quits from fuel starvation. Crank engine briefly to confirm pressure relief. NOTE: Some systems have two fuel pumps: low-pressure in-tank, and high-pressure in-line. Be sure to disable both fuel pumps when this applies.
2.WARNING: Gasoline vapors are explosive! To reduce the possibility of sparking, disable the electrical system by disconnecting the negative (-) battery cable.
3.Drain fuel to lighten the tank and avoid spilling when removing the pump hanger assembly. Use only an approved container, preferably one that filters the fuel for reuse in the vehicle.
4.Remove the fasteners for the fuel filler neck, noting their different sizes and locations, then raise vehicle on the hoist. (If working without a hoist, use an approved floor jack to raise the vehicle and approved jack stands to support it.)
5.Support the tank with a transmission stand or floor jack. Note location of fuel outlet, fuel return and vapor return lines. Remove the lines, using a clean shop towel to absorb draining fuel, and inspect them for cracking or chafing. When replacing high-pressure lines, use only SAE R-7 hoses or higher. Disconnect pump wiring harness.
6.Remove tank straps, and filler neck tube if necessary. Lower tank enough to access fuel pump hanger assembly, or completely remove tank.If tank is rusted inside, or seriously damaged, it must be repaired or replaced before proceeding. Also replace hangers that show excessive rust, wear or damage. Do not return sour or contaminated fuel to the vehicle. Dispose of properly.


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