Backfire. Oldsmobile Shelby Series 1 1999

For 1990-2009 cars

Checks | Actions
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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 powertrain control module (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 - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

• | Inspect that each injector harness is connected to the correct injector or cylinder according to the firing order. Relocate injector harnesses as necessary.

Sensor/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 the J 33431-B signal generator to the vehicle speed sensor (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.

• | 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:

- | 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 conditions:

- | Correct heat range

- | Wet plugs

- | Cracks

- | Wear

- | Improper gap

- | Burned electrodes

- | Heavy deposits

• | An improper spark plug gap causes a driveability concern. Gap the spark plugs using a wire gauge gap tool.

• | 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.

• | Visually and physically inspect secondary ignition for the following:

- | Ignition wires arcing to ground

- | Ignition wires for proper routing

- | 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 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.

• | Inspect the engine thermostat for proper operation and correct heat range.

Engine Mechanical

• | Inspect engine mechanical for the following:

- | Test compression

- | 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

• | For incorrect basic engine parts, inspect the following components:

- | Camshaft

- | Cylinder head

- | Pistons, etc.

Additional Checks

• | Visually and 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.

• | 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 three-way catalytic converters (TWC) for possible plugged pipes by comparing the exhaust system back pressure on each side of engine. Check back pressure by removing HO2S near exhaust manifolds.

• | 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.

• | Inspect for faulty engine mounts.

• | Inspect the intake manifold and the exhaust manifold passages for casting flash.