GM Service Manual Online
For 1990-2009 cars only

Checks

Action

DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases.

Preliminary

    •  Refer to Symptoms - Engine Controls .
    •  Search for service bulletins.
    • Connect a scan tool and look at the misfire data to possibly isolate a specific cylinder fault.

Fuel System

    • Inspect system fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .
    • Inspect the fuel filter for a plugged or restricted condition.
    • Inspect items which can cause an engine to run rich--Short term FT is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172 .
    • Inspect items that can cause an engine to run lean--Short term FT significantly in the positive range. Refer to Diagnostic Aids for DTC P0171 .
    • Inspect for proper operation of the evaporative emission (EVAP) control system.

Sensor/System

    • Inspect the oxygen sensor (O2S) 1. The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage--rich exhaust indication. The powertrain control module (PCM) will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
    • Inspect for proper operation of the manifold absolute pressure (MAP) sensor.
    • Inspect for proper operation of the throttle position (TP) sensor.
    • Inspect for proper operation of the engine coolant temperature (ECT) sensor.
    • Inspect for proper operation of the crankshaft position (CKP) sensor.
    • Inspect for proper operation of the camshaft position (CMP) sensor.

Ignition System

    • Inspect for proper ignition voltage output with a J 26792 Spark Tester or equivalent.
    • Using a scan tool, monitor cylinder misfire to pinpoint a specific cylinder.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel fouled spark plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes or heavy deposits
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect the spark plug wires for proper resistance and condition.

Engine Mechanical

    • Inspect engine mechanical for the following:
       - Compression--Refer to Engine Compression Test in Engine Mechanical 2.2L (L43).
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber and leaking valve seals
       - Low cylinder compression
    •  Inspect the following components for incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.2L (L43).

Additional Checks

    • Inspect the following components of the exhaust system for possible restrictions:
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - For possible plugged TWC--Refer to Restricted Exhaust in Engine Exhaust.
    •  An engine miss condition can be caused by electromagnetic interference (EMI) on the CKP reference circuit. EMI can usually be detected by monitoring medium resolution counter with a scan tool. A reading other than zero indicates EMI is present. If a problem exists, inspect routing of secondary ignition wires high voltage components--Near ignition control circuits.
    • Inspect for malfunctioning motor mounts.