Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Fuel Injector Tester (J-39021) and Injector Test Adapter (J-44602) are required for this procedure. See Fig 1
and Fig 2
.
- Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS in SELF-DIAGNOSTICS - 4.0L AURORA article. After performing Diagnostic System Check - Engine Controls, go to next step.
- Perform FUEL INJECTOR COIL TEST . After performing Fuel Injector Coil Test, go to next step.
- Observe ECT parameter using scan tool. Does scan tool indicate ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool before proceeding.
- Turn ignition off. Turn off all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Command fuel pump ON using scan tool. Observe fuel pressure gauge with fuel pump commanded ON. Is fuel pressure within 41-47 psi (284-325 kPa)? If yes, go to next step. If no, go to FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.0L AURORA article.
- Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.0L AURORA article. If no, go to next step.
- Connect Fuel Injector Tester and Injector Test Adapter to a fuel injector. Set amperage supply selector switch on fuel injector tester to Balance Test 0.5-2.5-amp position. Command fuel pump ON and then OFF using scan tool. Record fuel pressure indicated by fuel pressure gauge after fuel pressure stabilizes. This is first pressure reading. Energize fuel injector by depressing "Push to Start Test" button on fuel injector tester. Record fuel pressure indicated by fuel pressure gauge after fuel injector has stopped pulsing. This is second pressure reading. Repeat this step for each fuel injector. Subtract second pressure reading from first pressure reading for one fuel injector. Result is pressure drop value. See Fig 1 . Obtain a pressure drop value for each fuel injector. Add all individual pressure drop values. This is total pressure drop. Divide total pressure drop by number of fuel injectors. This is average pressure drop. Does any fuel injector have a pressure drop value more than average pressure drop or less than average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.0L AURORA article.
- Replace affected fuel injectors. See FUEL RAIL & INJECTORS under FUEL SYSTEMS in REMOVAL & INSTALLATION - AURORA article. After repairs, go to next step.
- Operate system in order to verify repair. Does a driveability condition still exist? If yes, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.0L AURORA article. If no, system is okay.
NOTE:
DO NOT perform this test if ECT is greater than 201°F (94°C).
NOTE:
Verify there is adequate fuel in fuel tank before proceeding with this step. Fuel pump may need to be commanded ON a few times, in order to obtain highest possible fuel pressure reading. DO NOT allow engine to start.
NOTE:
Fuel pressure may vary slightly when fuel pump stops operating. After fuel pump stops operating, fuel pressure should stabilize and remain constant.
NOTE:
Fuel pressure may rise after fuel injector stops pulsing. Record fuel pressure value immediately after fuel injector stops pulsing. DO NOT record higher fuel pressure value.