Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Procedure
- Did you perform the Diagnostic System Check - Engine Controls (Alternative Fuels). If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS (ALTERNATIVE FUELS) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.
- Did you perform the Fuel Injector Coil Test? If yes, go to next step. If no, go to FUEL INJECTOR COIL TEST .
- Start and idle the engine. Observe the fuel rail pressure sensor parameter using a scan tool. Is the fuel pressure 40-50 psi (276-345 kPa)? If yes, go to next step. If no, go to FUEL SYSTEM DIAGNOSIS (CNG) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE article.
- Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Monitor the fuel rail pressure sensor parameter using a scan tool. Does the fuel rail pressure remain constant? If yes, go to next step. If no, go to FUEL SYSTEM DIAGNOSIS (CNG) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE article.
- Turn ignition switch to OFF position. Connect the Fuel Injector Tester (J 39021), or equivalent, to a fuel injector. Set the amperage supply selector switch on the fuel injector tester to the BALANCE TEST 0.5-2.5 AMP position. Turn ignition switch to RUN position, engine OFF. Record the fuel pressure indicated by the fuel rail pressure sensor after the fuel pressure stabilizes. This is the first pressure reading. Record the fuel pressure value immediately after the CNG 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 CNG fuel injector by depressing the PUSH TO START TEST button on the fuel injector tester. Record the fuel pressure indicated by the fuel rail pressure sensor. 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 2.0 psi (14 kPa)? If yes, go to next step. If no, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.
- Replace the affected CNG fuel injector. After repair, go to next step.
- Operate the vehicle to verify the repair. Does a driveability condition still exist? If yes, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article. If no, system is okay at this time.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.