Symptoms Testing
Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable or Incorrect Idle and Stalling or Surges/Chuggles
- Test the fuel system for the following:
- The fuel system for correct operation volume and pressure. Refer Fuel System Diagnosis .
- The fuel injectors for proper operation. Refer to Fuel Injector Diagnosis (w/CH47976) .
- The fuel quality condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Test ignition system for the following:
- Proper ignition system operation-Refer to Electronic Ignition (EI) System Diagnosis .
- Spark plugs-Refer to Spark Plug Inspection .
- Spark plugs for correct application-Refer to Engine Mechanical Specifications .
- Inspect for the following conditions
- The proper operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis .
- The proper operation of the A/C compressor.
- Items that can cause an engine to run lean or rich. Refer to DTC P0171, P0172, P0174 or P0175 .
- The crankshaft position (CKP) sensor for proper operation
- The proper operation of the knock sensor (KS) system
- Inspect the exhaust system. Refer to Symptoms - Engine Exhaust .
- Electromagnetic interference (EMI) on the reference circuit can cause a misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter with little change in actual engine speed indicates that EMI is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
- The crankcase ventilation valve for proper operation.
- The proper operation of the evaporative emission (EVAP) canister purge solenoid.
- The proper operation of the engine cooling system-Refer to Symptoms - Engine Cooling .
- Inspect the engine for the following mechanical failures:
Refer to Symptoms - Engine Mechanical .
- Excessive oil in the combustion chamber or leaking valve seals
- Oil Consumption
- Incorrect cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Incorrect valve timing
- Worn rocker arms
- Broken valve springs
- Excessive carbon buildup in the combustion chambers-Clean the chambers with top engine cleaner. Follow the instructions on the can.
- Incorrect engine parts
- Correct engine oil pressure
- If the above conditions do not address the symptom, refer to the additional symptoms tests.