Engine Control System & Fuel System - 3.6L - Troubleshooting & Diagnosis: Backfire

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 system grounds for being clean, tight, and in the correct locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque.
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 (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Inspect that each injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or DTC P2187 .
Sensor/System	Inspect the air intake system and the crankcase for air leaks. Test the crankcase ventilation system for the correct operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.6L (LY7). Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 .
Ignition System	Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: For diagnosis of a rich condition, refer to DTC P2178 or DTC P2188 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures.
Engine Cooling System	Inspect the engine coolant level for being low. Refer to Draining and Filling Cooling System (GE 47716 Fill) or Draining and Filling Cooling System (LY7 Static Fill) in Engine Cooling. Inspect the engine thermostat for the correct operation and heat range. Refer to Thermostat Diagnosis (LY7) in Engine Cooling.
Engine Mechanical	Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers-Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (Third Design) or Camshaft Timing Drive Chain Alignment Diagram (Fourth Design) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings. Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection
Additional	Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on Vehicle Emission Control Information. Refer to Emission Hose Routing Diagram . Inspect the intake manifold and the exhaust manifold passages for casting flash. Test the transmission torque converter clutch (TCC). The scan tool should indicate a drop in engine speed when the TCC is commanded ON. Refer to Torque Converter Diagnosis in Automatic Transaxle - 4T65-E. Inspect the following exhaust system components: The exhaust system for damage The exhaust manifold for a collapsed inner wall. The mufflers for heat distress or possible internal failure The three-way catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed, indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. Test the park neutral position (PNP) switch circuit. Refer to DTC P0850 (3.6L) in Automatic Transaxle - 4T65-E.