GM Service Manual Online
For 1990-2009 cars only

Checks

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DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or low speed.

Preliminary

    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • Remove the air filter element and check for dirt or for being restricted. Refer to Air Cleaner Element Replacement . Replace as necessary.

Fuel System

    • Inspect the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect items that cause an engine to run rich long term fuel trim near -13 percent. For a rich condition, refer to DTC P0132 or P0152 .
    • Inspect items that can cause an engine to run lean (long term fuel trim near 24 percent. For a lean condition, refer to DTC P0131 or P0151 .

Sensor/System

Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity.

Ignition System

    • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water.
    • Test for proper ignition voltage output with J 26792 Spark Tester .
    • Remove the spark plugs and check for the following:
       - Correct heat range
       - Wet plugs
       -  Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits

Refer to Spark Plug Inspection .

    • An improper spark plug gap will cause a driveability problem. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gauge gap tool . Refer to Spark Plug Replacement .
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to DTC P0172 or P0175 for diagnosis of the rich condition. Refer to Spark Plug Inspection for diagnosis of coolant or oil fouled spark plugs.
    •  Visually and physically inspect the secondary ignition for the following:
       - Ignition wires arcing to ground
       - Ignition wires for proper engagement to spark plug
       - Ignition coils for cracks or carbon tracking
    • Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a cylinder can be located with a misfire, use the DTC P0300 table for diagnosis.

Engine Mechanical

    • Inspect engine mechanical for the following:
       - Inspect compression--Refer to Engine Compression Test in Engine Mechanical 4.8L, 5.3L, 6.0L.
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.
    •  For incorrect basic engine parts inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Refer to Engine/Engine Mechanical for diagnosis procedures.

Additional Checks

    • Inspect the exhaust system for possible restrictions. Inspect for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the exhaust manifold for a collapsed inner wall.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Inspect for possible plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of engine. Check back pressure by removing secondary air injection (AIR) check valves near exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust.
    • Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Check for high voltage components near ignition control circuits if a condition exists.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash.