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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 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 .
    • 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 .
    • Inspect that each injector harness is connected to the correct injector/cylinder according to the firing order (firing order: 1-8-7-2-6-5-4-3). Relocate 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 inlet hole in valve end several times. The valve should snap back. If not, replace the valve.
    • Inspect for proper calibration of the speedometer. Connect Signal Generator J 33431-B to the VSS electrical connector. Turn ON the ignition, the tester, and monitor the speedometer. The speedometer should indicate 86 km/h (54 mph). If not, refer to Gauge System Check in Instrument Panel, Gauges, and Console.
    • Use a scan tool in order to monitor the KS system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .

Ignition System
    • Test for proper ignition voltage output with spark tester J 26792 .
    • Inspect for an intermittent ignition system malfunction in the following circuits:
       - 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 for the following:
       - Correct heat range; refer to Spark Plug Usage in Engine Electrical.
       - Wet plugs; refer to Spark Plug Visual Diagnosis in Engine Electrical.
       - Cracks; refer to Spark Plug Visual Diagnosis in Engine Electrical.
       - Wear; refer to Spark Plug Visual Diagnosis in Engine Electrical.
       - Improper gap; refer to Spark Plug Replacement in Engine Electrical.
       - Burned electrodes; refer to Spark Plug Visual Diagnosis in Engine Electrical.
       - Heavy deposits; refer to Spark Plug Visual Diagnosis in Engine Electrical.
    • An improper spark plug gap causes a driveability concern. Gap the spark plugs 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, coolant or oil fouled. Refer to DTC P0172 Fuel Trim System Rich Bank 1 or DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition. Refer to Spark Plug Visual Diagnosis in Engine Electrical for diagnosis of coolant or oil fouled spark plugs.
    • Visually/Physically inspect secondary ignition for the following:
       - Ignition wires arcing to ground; refer to Spark Plug Wires Not Operating Properly in Engine Electrical.
       - Ignition wires for proper routing; refer to Spark Plug Wire Harness Replacement in Engine Electrical.
       - Ignition coils for cracks or carbon tracking
    • 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 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 compression. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Sticking or leaking valves. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Worn camshaft lobe(s). Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Valve timing. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Bent push rods. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Worn rocker arms. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Broken valve springs. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 5.7L.
    • For incorrect basic engine parts. Inspect the following components:
       - Camshaft
       - Cylinder head
       - Pistons, etc.
    • Refer to Engine Mechanical for the proper diagnosis procedures.

Additional Checks
    • Visually (physically) inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on 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 Functional Test in Automatic Transmission (4L60E).
    • Inspect the exhaust system for possible restrictions. Inspect the following:
       - Inspect the exhaust system for damaged or collapsed pipes. Refer to Restricted Exhaust System Check .
       - Inspect the exhaust manifold for a collapsed inner wall.
       - Inspect the mufflers for heat distress or possible internal failure. Refer to Restricted Exhaust System Check .
       - Inspect for possible plugged Three-Way catalytic converters by comparing exhaust system back pressure on each side of engine. Check back pressure by removing AIR check valves near exhaust manifolds. Refer to Restricted Exhaust System Check .
    • 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 actual engine RPM change, may indicate that EMI is present. If a problem exists, inspect for high voltage components near ignition control circuits.
    • Test the PNP switch circuit. Refer to DTC P0705 Trans Range Switch Circuit or DTC P0706 Trans Range Switch Performance .
    • Inspect for faulty engine mounts. Refer to Engine Mount Replacement 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.