GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Electrical 🢒 Surges/Chuggles

Checks

Action

DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.

Preliminary
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Check the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • Be sure the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owners manual. Inform the customer how the TCC and the A/C clutch operates.

Sensor/System
    • Check the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. If the HO2S do not, check the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white , powdery coating and result in a high but false signal voltage rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe driveability problem. For more information, refer to Oil Consumption Diagnosis in Engine Mechanical.
    • Check the mass air flow (MAF) sensor connections. Repair or replace terminals. Refer to Connector Repairs in Wiring Systems.

Fuel System
    • Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check that each injector harness is connected to the correct injector or cylinder according to the firing order: 1-8-7-2-6-5-4-3. Relocate injector harnesses as necessary.
    • Check the 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 .
    • Check the 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 .

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 the water.
    • Check for proper ignition voltage output with J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .
    • 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. Gap the spark plugs using a wire gage 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 Spark Plug Inspection for diagnosis of fouled spark plugs.
    • 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.
    • Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical

Check engine mechanical for the following:

    • Check compression--Refer to Engine Compression Test in Engine Mechanical.
    • 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 .

Additional Checks

Check vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.