GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firefly (Canada) 🢒 Engine 🢒 Engine Controls - 1.3L 🢒 Cuts Out, Misses

Checks

Action

DEFINITION: A steady pulsation or a jerky pulsation which follows engine speed, usually increasing as the engine load increases. The exhaust has a steady backfiring sound at idle, at a low speed, or on hard acceleration.

Preliminary Checks
    • Refer to Symptoms .

Ignition System Checks

Check for an ignition system misfire:

    Important: DO NOT perform this test for more than 2 minutes in order to prevent damage to the catalytic converter.

  1. Start the engine.
  2. Disconnect one fuel injector at a time while observing engine RPM.
  3. An equal RPM drop on all cylinders, within 50 RPM, indicates a common condition. Refer to Rough, Unstable, or Incorrect Idle and Stalling .
  4. If the RPM does not drop on one or more cylinders, a cylinder specific condition is indicated. Check for a spark on the suspected cylinders with J 26792 a spark tester or with an equivalent.
  5. If there is not a spark present, refer to Engine Cranks but Does Not Run .
  6. If there is a spark, check the spark plugs for any of the following conditions:
    7.  - Wet plugs
     - A loose or bent terminal screw
     - A ceramic insulator that has cracks, has carbon tracking, or has deposits
     - A tip insulator that has cracks, has carbon tracking, has deposits, or is loose
     - A center electrode that is loose
     - An incorrect spark plug gap that is too large or too small.
     - Refer to Spark Plug Visual Diagnosis in Engine Electrical.
  7. If the ignition system components of the suspected cylinder pass all checks, inspect the cylinder for mechanical faults or for fuel delivery faults.
  8. Check that the spark plug wire resistance does not exceed 30,000 ohms.
  9. Check the ignition system for moisture, for dust, for cracks, or for burns.
  10. Run the engine, and spray the secondary ignition system with water in order to check for secondary voltage shorts.
  11. Check the reference signal from the CKP sensor with a scan tool. Observe the engine speed parameter while operating the engine at the speed of the concern. The scan tool should indicate steady RPM readings and linear RPM readings while running. If sudden increases or decreases in engine speed are displayed, the engine reference signal is not stable enough for the engine to run correctly. Check for a short to ground in the ignition reference low circuit of the CKP sensor. A short to ground in the ignition reference low circuit of the CKP sensor will cause a faulty engine reference signal to be sent to the PCM. However, this will not set a CKP sensor DTC.

Engine Mechanical Checks
    • Check for any of the following engine mechanical conditions:
       - An incorrect valve lash
       - Broken valve springs or weak valve springs
       - Incorrect valve timing
       - An incorrect camshaft or a worn camshaft
    • Check the intake and the exhaust manifold passages for casting flash.

Fuel System Checks
    • Check for a restriction in the fuel supply system. Check for the correct fuel pressure. Refer to Fuel System Diagnosis .
    • Check the fuel injectors. Perform the Fuel Injector Coil Test and the Fuel Injector Balance Test. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and to Sequential Multiport Fuel Injector Balance Test .
    • Check for water contamination of the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Additional Checks
    • Check the PCM grounds for being clean, tight, and in the correct locations. Refer to

Cell 21: Power and Ground
Object Number: 278544 Size: FS
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    • Check the Service Bulletins for any updates or for any information.