Engine Controls - 1.6L (L91) Troubleshooting & Diagnosis): Troubleshooting: Backfire

Back Fire

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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. Verify that the engine control module (ECM) grounds are clean, tight, and in the correct locations.
Fuel System	Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . 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) . Verify that the fuel injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Coil Test . Test or inspect items that can cause an engine to run lean. For a lean condition, refer to DTC P0171 .
Sensor/System	Inspect the air intake system and the crankcase for air leaks. Test the crankcase ventilation valve. Refer to Crankcase Ventilation System Inspection/Diagnosis . 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 and DTC P0327 .
Ignition System	Test the ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . Inspect for an intermittent ignition system malfunction in the ignition control circuit. Use the Snapshot feature on the scan tool to locate an intermittent failure. Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Excessive wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: SPARK PLUG INSPECTION Spark Plug Replacement Ignition System Specifications An improper spark plug gap can cause a driveability concern. Refer to Ignition System Specifications . If the spark plugs are fouled by gas, coolant, or oil, determine the cause before replacing the plugs. Refer to the following procedures: For diagnosis of a rich condition, refer to DTC P0172 . For diagnosis of coolant or oil fouled spark plugs, refer to Loss of Coolant in Engine Cooling or Symptoms - Engine Mechanical in Engine Mechanical - 1.6L (L91). Inspect the spark plug wires for damage. Refer to SPARK PLUG WIRE INSPECTION . 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 the water is applied. Test the crankshaft position (CKP) sensor for the correct resistance. The CKP sensor resistance may be out of range after a hot soak. The resistance should be between 460-620 ohms. Inspect the ignition coil for cracks or carbon tracking.
Engine Cooling System	Inspect the engine coolant level. Refer to Draining and Filling Cooling System in Engine Cooling. Test the engine thermostat. Verify that the thermostat is of the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.
Engine Mechanical	Inspect for the following engine mechanical conditions: Incorrect compression Sticking or leaking valves Worn camshaft lobes Incorrect valve timing Broken valve springs Excessive oil in the combustion chamber or leaking valve seals For more information, refer to the following procedures in Engine Mechanical - 1.6L (L91): Oil Leak Diagnosis Engine Compression Test Symptoms - Engine Mechanical Inspect the following for incorrect basic engine parts: The camshaft The cylinder heads The pistons, connecting rods, and bearings Refer to the following procedures in Engine Mechanical - 1.6L (L91): Cylinder Head Replacement Camshaft Replacement Piston, Connecting Rod, and Bearings Cleaning and Inspection
Additional Checks	Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information label. Refer to Emission Hose Routing Diagram . Test the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Symptoms - Automatic Transmission in Automatic Transmission - Aisin (81-40LE). Inspect the following exhaust system components: 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 converter(s) for restrictions. For more information, refer to Symptoms - Engine Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase of the engine speed parameter with little change in actual engine speed may indicate that EMI is present. If a problem exists, inspect the high voltage components near the ignition control circuits.