GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Catera 🢒 Engine 🢒 Engine Controls - 3.0L (L81) 🢒 Backfire

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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 ECM 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 .
    • 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 Fuel Trim System Lean Bank 1 and DTC P0174 Fuel Trim System Lean Bank 2 .

Sensor/System
    • Test the secondary air injection (AIR) system. Refer to Secondary Air Injection System Diagnosis .
    • Inspect the air intake system and the crankcase for air leaks.
    • Test the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Diagnosis .
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Detonation/Spark Knock .

Ignition System
    • Test for proper ignition voltage output with J 26792 spark tester.
    • 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
    • An improper spark plug gap may cause a driveability concern. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement .
    • 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 Visual Diagnosis in Engine Electrical.
       - For diagnosis of a rich condition, refer to DTC P0172 Fuel Trim System Rich Bank 1 or to DTC P0175 Fuel Trim System Rich Bank 2 .
       - 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.

Engine Cooling System
    • Inspect the engine coolant level for being low. Refer to Cooling System Draining and Filling in Engine Cooling.
    •  Inspect the engine thermostat for proper operation and correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical
    • Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.
    • Check for incorrect camshaft timing. Refer to Timing Belt Timing Adjustment in Engine Mechanical.
    • For incorrect basic engine parts, inspect the following:
       - 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 Bearing Cleaning and Inspection in Engine Mechanical.

Additional Checks
    • 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. Refer to Intake Manifold Removal or Exhaust Manifold Cleaning and Inspection in Engine Mechanical.
    • 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 in Automatic Transmission-4L30-E.
    • Inspect the exhaust system for possible restrictions:
       - The exhaust system components for physical damage
       - The mufflers for heat distress or possible internal failure
       - The catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine. Refer to Restricted Exhaust System Check .
    • 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.
    • Test the PNP switch circuit. Refer to DTC P0705 Trans Range Switch Circuit or DTC P0706 Trans Range Switch Performance .