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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Backfire

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

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the PCM grounds for being clean, tight and in the proper locations. Refer to Engine Controls Schematics .

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

Sensor/System
    • Test the secondary air injection (AIR) system.
    • Inspect the air intake system and the crankcase for air leaks.
    • Test the crankcase ventilation valve for proper operation. Place a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve.
    • Inspect for proper calibration of the speedometer. Connect the J 33431-B signal generator to the vehicle speed sensor (VSS) electrical connector. Turn ON the ignition and the tester. Monitor the speedometer. The speedometer should indicate 86 km/h (54 mph). If not, refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges, and Console.
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .

Ignition System
    • Test for proper ignition voltage output with the J 26792 spark tester.
    • Inspect for an intermittent ignition system malfunction in the following circuits:
       - The ignition control circuit
       - Use the Snapshot feature on the scan tool in order to help locate an intermittent ignition failure.
    • Remove the spark plugs and inspect the plugs for the following conditions:
       - The correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
       -  Spark Plug Inspection
       -  Spark Plug Replacement
    • An improper spark plug gap causes a driveability concern. 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. If the spark plugs are gas, coolant, or oil fouled, refer to DTC P0172 or P0175 for diagnosis of the rich condition. Refer to Spark Plug Inspection for diagnosis of coolant or oil fouled spark plugs.
    • Visually and physically inspect the secondary ignition for the following conditions:
       - The ignition wires arcing to ground--Refer to Spark Plug Wire Inspection .
       - The ignition wires for proper routing--Refer to Spark Plug Wire Replacement .
       - The ignition coils for cracks or carbon tracking
    • Wet the secondary ignition system with water from a spray bottle. Wetting the secondary ignition system may help to locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
    • Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

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

Engine Mechanical
    • Inspect engine mechanical for the following:
       - Test the compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excess oil in the combustion chamber-Inspect for leaking valve seals
    • For more information, refer to one or more of the following procedures in Engine Mechanical-5.7L:
       -  Engine Compression Test
       -  Symptoms - Engine Mechanical
       -  Oil Consumption Diagnosis
    • Inspect for incorrect engine parts, such as the following basic components:
       - The camshaft
       - The cylinder head
       - The pistons

Additional Checks
    • Visually and physically inspect the vacuum hoses for splits, kinks, proper connections, and routing as shown on the Vehicle Emission Control Information label. Refer to Emission Hose Routing Diagram .
    • 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.
    • Test the transmission torque converter clutch (TCC) for proper operation. The scan tool should indicate an RPM drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis in Automatic Transmission-4L60E.
    • 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 3-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 Leakage
       -  Restricted Exhaust
    • Electromagnetic interference (EMI) on the reference 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 the actual engine RPM may indicate that EMI is present. If a condition exists, inspect for any high voltage components near the ignition control circuits.
    • Test the PNP switch circuit DTC P0706 in Automatic Transmission - 4L60-E.
    • Inspect for faulty engine mounts. Refer to Engine Mount Replacement - Left Side or Engine Mount Replacement - Right Side in Engine Mechanical-5.7L for inspection of the mounts.
    • 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.