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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 LaCrosse 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Backfire

Inspections

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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 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 .
    • 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 .
    • 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. 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:
    • 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 .
       - For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis .
       - 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 Cooling System Draining and Filling .
    •  Inspect the engine thermostat for the correct operation and heat range. Refer to Thermostat Diagnosis .

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:
    • Inspect the following components for incorrect basic engine parts:
       - Camshafts
       - Cylinder heads
       - Pistons, connecting rods, or bearings.
       - Refer to the following procedures:

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 .
    • 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 .
    • 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 .