GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Cuts Out, Misses

Checks

Action

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

Preliminary
    • Refer to Symptoms .
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight and in their proper locations. Refer to Wiring Repairs in Wiring Systems.
    • Remove the air filter element and check for dirt or for being restricted. Refer to Air Cleaner Element Replacement . Replace as necessary.

Fuel System
    •  Perform the injector balance test. Refer to Sequential Multiport Fuel Injector Balance Test for procedure.
    •  Check for a low fuel pressure condition. 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 items which can cause an engine to run rich (long term fuel trim near -13%). 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 .
    • Check items that can cause an engine to run lean (long term fuel trim near 23%). 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

Use a scan tool in order to monitor the 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/listen for arcing or misfiring as you apply water.
    • Check for proper ignition voltage output with spark tester J 26792 .
    • Remove the spark plugs and check for the following:
       - Correct heat range.
       - Wet plugs
       -  Cracks
       -  Wear
       -  Improper gap
       -  Burned electrodes
       -  Heavy deposits
    • An improper spark plug gap will cause a driveability problem. Do the spark plug gapping using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement. Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas or oil fouled. Refer to Fuel System Diagnosis for diagnosis of the rich condition or for diagnosis of the oil fouling condition.
    •  Visually/Physically inspect the Secondary ignition for the following:
       - Ignition wires for cross firing
       - Ignition wires arcing to ground
       - Ignition wires for proper routing
       - Ignition coils for cracks or carbon tracking
    • Refer to Engine Mechanical

Engine Mechanical
    • Check engine mechanical for the following:
       -  Check 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
       - Low cylinder compression
    • Refer to Engine Mechanical
    •  For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    •  Refer to Engine Mechanical for diagnosis procedures.

Additional Checks
    • Check exhaust system for possible restrictions. Check 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 catalytic converters by comparing exhaust system back pressure on each side of engine. Check the back pressure by removing Heated Oxygen Sensor (HO2S) near exhaust manifolds.
    •  Refer to Restricted Exhaust System Check .
    • 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 EMI is present. Check routing of secondary ignition wires, high voltage components (Near Ignition Control circuits) if a problem exists.
    • Check the intake manifold and the exhaust manifold passages for casting flash. Refer to Intake Manifold Cleaning and Inspection and Exhaust Manifold Clean and Inspect (without RPO K19) in Engine Mechanical.