Diagnostic Procedure
- Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. After performing diagnostic system check - engine controls, go to next step.
- Did you perform the Fuel Injector Coil Test? If yes, go to next step. If no, go to FUEL INJECTOR COIL TEST .
- Observe the ECT parameter on the scan tool. Does the scan tool indicate that the ECT parameter is less than 201°F (94°C)? If yes, go to next step. If no, allow engine to cool below 201°F (94°C), then go to next step.
- Turn ignition switch to OFF position. Turn OFF all accessories. Install Fuel Pressure Gauge (J 34730-A), or equivalent. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. The fuel pump may need to be commanded ON a few times to obtain the highest possible fuel pressure. DO NOT start the engine. Observe the fuel pressure gauge, with the fuel pump commanded ON. Is the fuel pressure 52-59 psi (358-407 kPa)? If yes, go to next step. If no, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
- Monitor the fuel pressure gauge for one minute. Does the fuel pressure decrease by more than 5 psi (34 kPa)? If yes, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to next step.
- Connect the Fuel Injector Coil/Balancer Tester (J 39021), Injector Selector Switch Box (J 39021-210), and Fuel Injector Harness Adapter (J 39021-410), or equivalents, to the fuel injector multi-way connector. Set the amperage supply selector switch on the fuel injector tester to the balance test 0.5-2.5 AMP position. Command the fuel pump relay ON and then OFF using a scan tool. Record the fuel pressure indicated by the Fuel Pressure Gauge (J 34730-1A), or equivalent, after the fuel pressure stabilizes. This is the first pressure reading. See Fig 1. Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the PUSH TO START TEST button on the fuel injector tester. Record the fuel pressure indicated by the fuel pressure gauge. This is the second fuel pressure reading. Repeat procedure for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by 1.5 psi (10 kPa)? If yes, go to next step. If no, diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
- Clean the fuel injector. See FUEL INJECTOR CLEANING . After repair, go to next step.
- Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
NOTE:
DO NOT perform this test if the Engine Coolant Temperature (ECT) is above 201°F (94°C).
NOTE:
Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic procedure.
NOTE:
The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.