GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Cobalt 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Backfire

Inspections

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DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.

Preliminary Inspections
    • Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .

Fuel System
    • Test 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 .
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Verify that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses, as necessary.

Sensor/System
    • Inspect the air intake system and crankcase for air leaks.
    • Inspect the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 2.2L.
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Scan Tool Data List .

Ignition System
    • In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
       -  Spark Plug Inspection
       -  Spark Plug Replacement
    • Remove spark plugs and inspect for the following:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Verify that the spark plugs are of the correct type.
    • Inspect for proper ignition voltage output with J 26792 Spark Tester .
    • An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool.
    • Determine the cause of the fouling before replacing the spark plugs.
    • Inspect for damaged or misaligned spark plug boots.
    • Inspect the electronic ignition (EI) module for proper ground connection.
    • Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .

Engine Cooling System
    • Inspect the engine coolant level for being low. Refer to Loss of Coolant in Engine Cooling.
    • Inspect the engine thermostat for proper operation and for the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical - 2.2L for diagnosis procedures.
    • Inspect engine mechanical for the following:
       - Compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber or leaking valve seals.
       - For more information, refer to one or more of the following procedures in Engine Mechanical - 2.2L:
    • For incorrect basic engine parts. Inspect the following:
       - The camshaft--Refer to Camshaft Cleaning and Inspection in Engine Mechanical - 2.2L.
       - The cylinder heads--Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical - 2.2L.
       - The pistons, etc.--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in Engine Mechanical - 2.2L.

Additional Inspections
    • Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash.
    • Inspect the exhaust system for possible restrictions. Inspect 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 catalytic converter. Refer to Restricted Exhaust in Engine Exhaust.
    • Electromagnetic interference (EMI) circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change may indicate that EMI is present. If a problem exists, inspect for high voltage components near the ignition control circuits.