Symptom Checks

Check the following items:

• Check cooling system for overheating. If cooling system is overheating, go to ENGINE RUNS HOT symptom.
• Check engine mechanical condition. Check compression, camshaft, valve train components, etc.
• Check fuel delivery system. See CIRCUIT TEST HC in TESTS W/CODES article.
• Check secondary ignition system. See CIRCUIT TEST JB in TESTS W/CODES article.
• Check PCV system. See CIRCUIT TEST HB in TESTS W/CODES article.
• On vehicles with OCT ADJ circuit (PCM terminal No. 30), check octane adjust input to PCM. See CIRCUIT TEST FG, step 5) in TESTS W/CODES article.
• On vehicles with Knock Sensor (KS), check KS input to PCM. See CIRCUIT TEST DG in TESTS W/CODES article.
• Check intake air system. Check engine oil quality. If available, check Technical Service Bulletins (TSBs) for octane adjust information. If no problems are indicated, return to SYMPTOM DIAGNOSIS  to identify any additional symptoms or go to CIRCUIT TEST Z in TESTS W/CODES article and check for intermittent faults.