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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 112 (Engine Controls - Self-Diagnostics - 3.0L) >> Diagnostic Tests >> DTC P0301-P0306: Specific Cylinder Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If a fuel injector DTC is also set, diagnose that DTC first.
  1. Ensure fuel level is greater than 1.6 gallons. Operate engine for one minute. Using scan tool, monitor current misfire counter. If any misfire counters are incrementing, go to next step. If no misfire counters are incrementing, problem is intermittent. See DIAGNOSTIC AIDS  .
  2. If only one cylinder misfire counter is dominant, go to next step. If more than one misfire counter is dominant, see DTC P0300: ENGINE MISFIRE DETECTED  .
  3. Turn ignition on, engine off. Using scan tool, perform IGNITION COIL CYL. 1-6 test on cylinder that is missing, while listening for audible spark at that cylinder. If spark is consistently audible for the misfiring cylinder, go to next step. If spark is not consistently audible for the misfiring cylinder, go to step  6 .
  4. Turn ignition on, engine off. Perform an injector balance test. Use scan tool to perform FUEL INJECTOR FLOW TEST for each cylinder. ECM will automatically run the fuel pump for 4 seconds each time an injector is pulsed. Note the pressure drop for each injector. Take the most common pressure drop reading and use that as a gauge against the other injectors. If pressure drop is consistent within 1.5 psi, go to next step. If pressure drop is not consistent within 1.5 psi, check injector for correct resistance. If resistance is okay, clean or replace injector.
  5. Perform compression test. If compression is okay, check for fouled spark plug or sticking intake/exhaust valve. If compression is not okay, repair engine. See appropriate article in ENGINES.
  6. Disconnect misfiring cylinder EI module harness connector. Connect a high impedance test light between battery voltage and misfiring cylinder ECM primary coil control circuit. Using scan tool, perform IGNITION COIL CYL. 1-6 test on the misfiring cylinder. If test light is always off, go to next step. If test light is always on, check for shorted to ground in ECM primary coil control circuit. If ECM primary coil control circuit is okay, replace ECM. If test light pulses correctly, go to step  8 .
  7. Connect high impedance test light between misfiring cylinder ECM primary coil control circuit and ground at harness connector. If test light is on, repair ECM primary coil control circuit shorted to voltage. If test light is off, check for open in ECM primary coil control circuit. If ECM primary coil control circuit is okay, replace ECM.
  8. Remove misfiring cylinder EI module/coil assembly. Remove misfiring cylinder spark plug. Remove misfiring cylinder spark plug boot from EI module. Check spark plug and spark plug boot for carbon tracking, pitting, cracking corrosion, wear and correct spark plug gap (0.045"). If spark plug and boot are okay, check EI module harness connector. If connector is okay, replace EI module. If spark plug and boot are not okay, replace components as necessary. Retest engine for misfire.
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