Fuel System Diagnosis

Note: The following test ,procedures assume that the ignition system is functioning and that a good spark is present at the plugs. If this is not the case, diagnose and repair any ignition system problems before proceeding with fuel system testing.
1. Remove the air cleaner and disconnect the fuel injector electrical connector from the throttle body.
2. Using the appropriate tester (DRB II or equivalent scan tool), place ignition switch in "RUN" position and use Actuate Output Test "Auto Shutdown (ASD) Relay", to activate fuel pump and pressurize system.
3. Inspect the top of the fuel pressure regulator and replace regulator if there is evidence of fuel wetness.
4. With system still pressurized inspect fuel injector for fuel leaks.
^ If there is fuel leaking from the injector go to step 5.
^ If there is no fuel dripping from the injector the problem is computer related.

Fuel Pressure Release:

5. Loosen fuel tank filler cap to relieve fuel tank pressure. Connect a jumper wire from one terminal of the injector side of the injector connector to ground. Connect a second jumper wire to the other terminal, and touch wire to the positive battery post for 10 seconds. System pressure is now released.
6. Carefully remove 5/16 fuel supply hose from the engine fuel line assembly and connect fuel pressure gauge C-3292, and hose adapter C-4799 or equivalents between supply hose and fuel line assembly.

Fuel Pressure Testing Equipment:

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7. Using the appropriate tester (DRB II or equivalent scan tool), place ignition switch in "RUN" position and use Actuate Output Test "Auto Shutdown (ASD) Relay", to activate fuel pump and pressurize system. This test will activate the fuel pump for 1.5 second intervals. The gauge should read 100 kPa plus or minus 7 kPa, (14.5 psi plus or minus 1 psi).
^ If pressure is as specified go to step 11.
^ If fuel pressure is below 93 kPa (13.5 psi) proceed to step 8.
^ If fuel pressure is above 111 kPa (16.0 psi) proceed to step 9.
8. If fuel pressure is below specification, remove pressure gauge from fuel supply line and install gauge between fuel tank and fuel filter. Repeat test procedure, and check fuel system pressure.
^ If pressure is 5 psi higher than previous reading and within specification, replace fuel filter. Service and Repair
^ If no change occurs in pressure proceed to step 9.
9. Gently squeeze fuel return hose while observing fuel pressure.
^ If pressure increases to specification replace fuel pressure regulator. Service and Repair
^ If no change in pressure occurs, replace the in tank pump and sock type filter. Service and Repair
10. If fuel pressure is above 111 kPa (16.0 psi) remove fuel return hose from fuel return nipple, and install a suitable hose to fuel return nipple. Place the other end of the hose in a large (2 gallon minimum), clean and approved container. START engine and observe fuel pressure.
^ If pressure is now within specification, problem is a restriction in fuel return line, or an obstructed fuel return check valve in tank. Clear return line obstruction if necessary, and/or replace fuel tank assembly if in-tank check valve is obstructed.
^ If pressure is still above specification replace fuel pressure regulator. Service and Repair
11. Turn ignition "OFF", and remove the fuel injector from the throttle body. [1][2]Fuel Injector Replacement
12. Inspect the lower injector O-ring.
^ If the O-ring is damaged, worn or misaligned repair or replace as needed.
^ If the O-ring is not worn, damaged or misaligned replace the fuel injector. [1][2]Fuel Injector Replacement