Possible Causes & Corrections

Check the following items:

• Search for bulletins.
• Verify that the PCM grounds are clean, tight and in the proper locations.
• Remove air filter element and inspect for dirt and for restrictions.
• Inspect fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 2.2L SONOMA & S10 PICKUP article.
• Inspect for incorrect fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 2.2L SONOMA & S10 PICKUP article.
• Inspect for a restricted fuel filter.
• Inspect for a contaminated fuel condition.
• Check for these conditions that will cause engine to run rich: Water intrusion in the HO2S connector, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, a leaking fuel pressure regulator, leaking fuel injectors or vacuum hoses that are split, kinked or improperly connected. Check for air intake duct that is collapsed or restricted, or an air filter that is dirty or restricted.
• Check for these conditions that cause engine to run lean: Water intrusion in HO2S connector, exhaust leak between HO2S and engine, any vacuum leaks, incorrect fuel pressure, restricted fuel injectors, fuel contamination or vacuum hoses that are split, kinked or improperly connected.
• Use a scan tool in order to monitor the Knock Sensor (KS) system for excessive spark retard activity.
• Inspect Oxygen Sensor No. 1 (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicone or other contaminants from fuel or the use of improper RTV sealant. The sensors may have a White powdery coating. Silicone contamination causes a high but false O2S 1 signal voltage, a rich exhaust indication. The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
• Inspect for proper operation of the Manifold Absolute Pressure (MAP) sensor. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
• Inspect for proper operation of the Throttle Position (TP) sensor. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
• Inspect for proper operation of the Crankshaft Position (CKP) sensor. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
• Inspect for proper operation of the Camshaft Position (CMP) sensor. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
• Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water.
• Test for proper ignition voltage output with a Spark Tester (J-26792).
• Remove spark plugs and inspect for correct heat range, wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
• An improper spark plug gap will cause a driveability problem.
• Determine cause of fouling before replacing spark plugs.
• Visually and physically inspect the secondary ignition for ignition wires arcing to ground, ignition wires for proper engagement to spark plug, ignition coils for cracks or carbon tracking.
• Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use DTC P0300 diagnostic procedures for diagnosis. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
• Inspect engine compression. Low compression could be caused by a sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms, broken valve springs. Check for excessive oil in combustion chamber, caused by leaking valve seals.
• Check for incorrect basic engine parts, such as the camshaft, cylinder heads or pistons, etc.
• Check exhaust system for possible restrictions. Inspect for exhaust system for damaged or collapsed pipes. Inspect mufflers for heat distress or possible internal failure. Inspect for possible plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of engine. Inspect back pressure by removing Secondary Air Injection (AIR) check valves near exhaust manifolds.
• Electromagnetic Interference (EMI) on the reference circuit can cause an engine misfire condition. A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits, if a condition exists.
• Inspect intake and exhaust manifold passages for casting flash.