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DTC P0300: Random Misfire Detected, Or P0301-P0304 Cylinders No. 1-4 Misfire Detected

NOTE: Ensure engine compression, valve adjustment and ignition timing are within specification before proceeding with following test. Go to BASIC DIAGNOSTIC PROCEDURES article. If any DTCs besides DTC P0171, P0172 or P0300-P0304 are set, diagnose those DTCs first.
  1. Remove spark plugs and check for proper gap. Check for carbon deposits or cracked insulators. Repair as necessary. Disconnect all injector harness connectors. Using a spark tester, ensure a strong, Blue spark is present at each plug wire. If a strong, Blue spark is present at each plug wire, reconnect injector harness connectors and go to next step. If no spark or a weak spark is present, check ignition system components. Go to IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article.
  2. Check fuel pressure. Go to FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. With key on and engine off, fuel pressure should be 38-44 psi (2.7-3.1 kg/cm2 ). With engine running at idle, fuel pressure should be 28-34 psi (2.0-2.4 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST B-3: FUEL PRESSURE INSPECTION under CIRCUIT TESTS in BASIC DIAGNOSTIC PROCEDURES article.
  3. Inspect fuel injectors and fuel system circuit. Go to CIRCUIT TEST B-1: FUEL INJECTOR CIRCUIT INSPECTION under CIRCUIT TESTS in BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. Retest system. If fuel system is okay, go to next step.
  4. Disconnect PCV valve from valve cover. Start engine and let idle. Check for vacuum at PCV valve. If vacuum is not present, disconnect PCV valve from hose. If engine runs rough or stalls, replace PCV valve. If engine does not run rough or stall, check for restriction in PCV hose. Repair as necessary. If PCV system is okay, go to next step.
  5. Turn ignition off. Allow engine to cool. Disconnect purge hose from EVAP canister. Start and idle engine. Place finger over end of disconnected hose. If no vacuum exists, go to next step. If vacuum exists, check EVAP canister purge valve. Go to FUEL EVAPORATION in SYSTEM & COMPONENT TESTING article. Repair as necessary. Retest system.
  6. Check MAP sensor performance. Go to DTC P0106: MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR PERFORMANCE  . Repair as necessary. If MAP sensor performance is okay, go to next step.
  7. Check ECT sensor performance. Go to ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. Repair as necessary. If ECT sensor performance is okay, go to next step.
  8. Check PCM harness connections and grounds for corrosion or loose terminals. Repair as necessary. If connections are okay, check for an intermittent problem. Go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. Repair as necessary. Retest system.
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