Section 10 (Engine Controls - 2.6L & 3.2L - Troubleshooting & Diagnosis): Troubleshooting: Backfire

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Backfire

Inspections	Actions
DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Preliminary	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	Inspect the fuel system. Refer to Fuel System Diagnosis . Test for incorrect fuel pressure. Test for a restricted fuel filter. Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/ Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect that each injector harness is connected to the correct injector/cylinder. Relocate injector harnesses as necessary. Inspect the items that can cause an engine to run lean, long term fuel trim near 23 percent. For a lean condition, refer to DTC P0171 or P0174 .
Sensor/System	Inspect the air intake system and the crankcase for air leaks. Test the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Scan Tool Data List .
Ignition System	Test for proper ignition system operation. Inspect for an intermittent ignition system malfunction in 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 for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to Spark Plug Inspection . Once you determine the cause of the fouling, refer to one of the following procedures: For diagnosis of a rich condition, refer to DTC P0172 or P0175 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant (M 35) or Loss of Coolant (M 82) in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical.
Engine Cooling System	Inspect the engine coolant level for being low. Refer to Draining and Filling Cooling System (LA3, LY9) , Draining and Filling Cooling System (LY7) or Draining and Filling Cooling System (LS6) in Engine Cooling. Inspect the engine thermostat for proper operation and correct heat range. Refer to Thermostat Diagnosis (LA3, LY9) , Thermostat Diagnosis (LY7) or Thermostat Diagnosis (LS6) in Engine Cooling.
Engine Mechanical	Excessive oil in combustion chamber due to leaking valve seals-Refer to Oil Consumption Diagnosis in Engine Mechanical. Inspect for incorrect camshaft timing-Refer to Timing Belt Timing Procedure in Engine Mechanical. Inspect the following components for incorrect basic engine parts: Camshafts-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. Cylinder heads-Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. Pistons, connecting rods or bearings-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical.
Additional	Visually/physically inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label or in Emission Hose Routing Diagram . Inspect the intake manifold and the exhaust manifold passages for casting flash. 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 Procedure in Automatic Transmission. Inspect the exhaust system for the following possible restrictions: The exhaust system components for physical damage-Refer to Restricted Exhaust in Engine Exhaust. The catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine-Refer to Restricted Exhaust in 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, may indicate that EMI is present. If a problem exists, inspect for high voltage components near ignition control circuits. Test the park neutral position (PNP) switch circuit. Refer to DTC P0850 .