GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 Sonoma Pickup - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 Cuts Out, Misses

Inspections

Action

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 Inspections Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .
    • Remove the air filter element and inspect for dirt and for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary.

Fuel System
    • Inspect the fuel injectors. Refer to Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test with Tech 2 .
    • 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 for the following that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Water intrusion in the HO2S connector
       - Engine oil contaminated by fuel
       - An EVAP canister purge condition
       - Incorrect fuel pressure--Refer to Fuel System Diagnosis .
       - A leaking fuel pressure regulator--Refer to Fuel System Diagnosis .
       - Leaking fuel injectors--Refer to Fuel System Diagnosis .
       - Any vacuum hoses that are split, kinked, or improperly connected
       - An air intake duct that is collapsed or restricted
       - An air filter that is dirty or restricted--Refer to Air Cleaner Element Replacement .
    • Inspect for the following conditions that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Water intrusion in the HO2S connector
       - An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.
       - Any vacuum leaks
       - Incorrect fuel pressure--Refer to Fuel System Diagnosis .
       - Restricted fuel injectors--Refer to Fuel System Diagnosis .
       - Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Vacuum hoses that are split, kinked, or improperly connected

Sensor/System
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity.
    • 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, a 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. Refer to DTC P0105 .
    • Inspect for proper operation of the throttle position (TP) sensor. Refer to DTC P0105 .
    • Inspect for proper operation of the engine coolant temperature (ECT) sensor. Refer to Temperature Versus Resistance .
    • Inspect for proper operation of the crankshaft position (CKP) sensor. Refer to DTC P0336 .
    • Inspect for proper operation of the camshaft position (CMP) sensor.

Ignition System
    • Soak the secondary ignition system with water from a spray bottle. Soaking 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 the J 26792 Spark Tester .
    • Remove the spark plugs and inspect 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.
    •  Visually and physically inspect the secondary ignition for the following:
       - The ignition wires arcing to ground
       - The ignition wires for proper engagement to spark plug
       - The 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 misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .

Engine Mechanical
    • Inspect engine mechanical for the following:
       - Inspect 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.
    •  For incorrect basic engine parts inspect the following:
       - The camshaft--Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical.
       - The cylinder heads--Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical.
       - The pistons, etc.--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in Engine Mechanical.

Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnostic procedures.

Additional Inspections
    • Inspect the exhaust system for possible restrictions. Inspect for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - 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. Inspect 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 misfire condition. A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits if a condition exists.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash.