GM Service Manual Online
For 1990-2009 cars only

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DEFINITION: A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or at low speed.

Preliminary

    • Refer to Important Preliminary Inspections Before Starting in Symptoms .
    • Search for bulletins.
    • Inspect the PCM grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • Remove the air filter element and inspect for dirt or for being restricted. Refer to Air Cleaner Element Replacement . Replace if necessary.

Fuel System

    • Test for proper fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect the items which can cause an engine to run rich (long term fuel trim near -13 percent). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .
    • Inspect items that can cause an engine to run lean (long term fuel trim near 23 percent). For a lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

Sensor/System

  1. Use a scan tool in order to monitor the KS system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .
  2. An Extended Travel Brake Switch that is mis-adjusted or an Extended Travel Brake circuit that is open causes a perceived misfire under heavy load conditions from a stop. Use a scan tool in order to monitor the Extended Travel Brake Switch parameter. If the scan tool displays Extended Travel Brake Switch applied when the brake pedal is released refer to DTC P1575 Extended Travel Brake Switch Circuit .

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/listen for arcing or misfiring as you apply water.
    • Test for proper ignition voltage output with spark tester J 26792 .
    • Remove the spark plugs and inspect for the following conditions:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • To properly inspect the spark plugs or to correct a problem, refer to the following procedure in Engine Electrical:
       -  Spark Plug Usage
       -  Spark Plug Visual Diagnosis
       -  Spark Plug Replacement
    • An improper spark plug gap will cause a driveability concern. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement in Engine Electrical.
    • 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 Fuel Trim System Rich Bank 1 or DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition. Refer to Spark Plug Visual Diagnosis in Engine Electrical for diagnosis of coolant or oil fouled spark plugs.
    • Visually/physically inspect the secondary ignition for the following:
       - Ignition wires arcing to ground
       -  Refer to Spark Plug Wire Resistance in Engine Electrical.
       - Ignition wires for proper routing
       - Refer to Spark Plug Wire Harness Replacement in Engine Electrical.
       - Ignition coils for cracks or carbon tracking

Engine Mechanical

    • Inspect engine mechanical for the following:
       - Test compression
       - 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
    • For more information, refer to one or more of the following procedures in Engine Mechanical-5.7L:
       -  Engine Compression Test
       -  Valve Train Diagnosis
       -  Oil Consumption Diagnosis
    • For incorrect basic engine parts, inspect the following components:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks

    • Inspect the following exhaust system components for possible restrictions:
       - The exhaust system for physical damage
       - The exhaust manifold for a collapsed inner wall
       - The mufflers for heat distress or possible internal failure
       - The Three-Way catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine
    • For more information, refer to the following procedures in Engine Exhaust:
       -  Exhaust System Inspection
       -  Restricted Exhaust
    • Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A sudden increase in RPM with little change in actual engine RPM change indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash. Refer to Intake Manifold Cleaning and Inspection or Exhaust Manifold Cleaning and Inspection in Engine Mechanical-5.7L.