GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1997 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Backfire

Checks

Actions

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

Preliminary Checks
    • Refer to Symptoms , Important Preliminary Checks Before Starting.
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight and in their proper locations. Refer to PCM wiring diagrams .

Fuel System
    • 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 Test .
    • Check 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
    • Check the Secondary Air Injection (AIR) system.
    • Check the Air intake system and crankcase for air leaks.
    • Check 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.
    • Check for proper calibration of speedometer. Connect Signal Generator J 33431-B to VSS electrical connector. Ignition ON, tester ON and monitor the speedometer. The speedometer should indicate 86 km/h (54 mph). Refer to Body and Accessories/Instrument Panel, gages and Console .

Use a scan tool in order to monitor the KS system for excessive spark retard activity. Refer to Knock Sensor (KS) System .

Ignition System
    • Check for proper ignition voltage output with spark tester J 26792 .
    • Check for an intermittent ignition system malfunction in the following circuits:
       - Intermittent ignition control circuit.
       - Use the scan tool's Snapshot feature in order to help locate an intermittent ignition failure.
    • Remove spark plugs and check for the following:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap will cause a driveability problem. Refer to Engine Electrical/Spark Plugs . Do the spark plug gapping using a wire gauge gap tool (J 41319). Refer to Engine Electrical/Spark Plug . Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas or oil fouled. Refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition or Engine/Engine Mechanical for diagnosis of the oil fouling condition.
    • Visually/Physically inspect secondary ignition for the following:
       - Ignition wires for cross firing
       - Ignition wires arcing to ground
       - Ignition coils arcing to ground
    • 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.
    • Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Check .

Engine Cooling System
    • Check the engine coolant level for being low. Refer to Engine/Engine Cooling.
    •  Check the engine thermostat for proper operation or for the wrong heat range. Refer to Engine/Engine Cooling .

Engine Mechanical
    • Check engine mechanical for the following:
       - Check compression
       - Sticking or leaking valves
       - Worn camshaft lobe(s)
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber-Leaking valve seals
       - Low cylinder compression
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Engine/Engine Mechanical for diagnosis procedures.

Additional Checks
    • Visually (physically) check the vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.
    • Check the intake manifold and the exhaust manifold passages for casting flash. Refer to Engine/Engine Mechanical .
    • Check the TCC operation. The scan tool should indicate an RPM drop when the TCC is commanded ON. Refer to Transmission/Transaxle/Automatic Transmission .
    • Check the exhaust system for possible restrictions. Check 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 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 and Engine/Engine 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 actual engine RPM change, may indicate that EMI is present. If a problem exists, check the routing of the secondary ignition wires or high voltage components near ignition control circuits.
    • Check the PNP switch circuit. Refer to DTC P0705 or P0706.
    • Check for faulty motor mounts. Refer to Engine/Engine Mechanical for inspection of the mounts.
    • Check the intake manifold and the exhaust manifold passages for casting flash. Refer to Engine/Engine Mechanical.