Possible Causes & Corrections
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Check the following items:
- Search for bulletins.
- Verify that 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 - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
- Inspect for incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
- Inspect for a restricted fuel filter.
- Inspect for a contaminated fuel condition.
- Inspect for conditions that may cause engine to run rich: Water intrusion in HO2S connector, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, leaking fuel injectors, inaccurate MAF sensor, blockage MAF sensor inlet screen, vacuum hoses that are split, kinked, or improperly connected, air intake duct that is collapsed or restricted, or air filter that is dirty or restricted.
- Inspect for conditions that may cause engine to run lean: Water intrusion in HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, restricted fuel injectors, inaccurate MAF sensor, fuel contamination or vacuum hoses that are split, kinked, or improperly connected.
- Monitor Knock Sensor (KS) system for excessive spark retard activity. SeeDIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article or DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE 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 the 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 or ignition coils for cracks or carbon tracking.
- Using scan tool, monitor the Misfire Current Counters while driving 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 - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article or DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE article.
- Inspect engine mechanical for compression, sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms, broken valve springs or excessive oil in combustion chamber, caused by leaking valve seals. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
- For incorrect basic engine parts. Inspect camshaft, cylinder heads, pistons, etc.
- Inspect for excessive crankshaft end play that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. This could result in a no-start, a start and stall, or an erratic performance.
- Inspect exhaust system for possible restrictions. Inspect exhaust system for damaged or collapsed pipes. Inspect mufflers for heat distress or possible internal failure. Inspect for possible plugged catalytic converters.
- 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.