Symptoms Testing

Backfire, Cuts-Out, Misses, Detonation/Spark Knock, Dieseling/Run-On, ECM Commanded Reduced Engine Power, Fuel Odor, Hard Start, Poor Fuel Economy, or Rough, Unstable, or Incorrect Idle and Stalling.

• Test/inspect the fuel system for the conditions listed below:
  • Incorrect system operation or fuel pressure. Refer to Fuel System Diagnosis .
  • Leaking or incorrectly operating fuel injectors. Refer to Fuel Injector Diagnosis .
  • Contaminated or poor quality fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Test/inspect the ignition system for the conditions listed below:
  NOTE:

  Observe the scan tool Cylinder 1 - 4 Current Misfire Counters and the Ignition Coil Control Circuit Status parameters to help isolate an ignition system condition.

  • Spark plugs with incorrect heat range, coolant or oil fouling, or an abnormal condition. Refer to Spark Plug Replacement .
  • Secondary ignition system component susceptible to moisture. Wet down the secondary ignition system with water from a spray bottle. This may help locate damaged or deteriorated ignition system components. Look/listen for arcing or misfiring as the water is applied.
  • Weak spark. Use the J-26792  HEI Spark Tester for testing and refer to Electronic Ignition System Diagnosis . For equivalent regional tools, refer to Special Tools .
• Test/inspect for the conditions listed below:
  • Non-metered air flow into the air induction system. If a leak is found, repair as necessary. The Q38 THROTTLE BODY: THROTTLE/IDLE LEARN procedure must be performed when the repair is complete.
  • Items that can cause an engine to run lean or rich. Refer to DTC P0171 or P0172 for additional information.
  • An intermittent crankshaft position sensor condition. Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter parameter should remain at 0 during all operating conditions, and when moving the related harnesses and connectors between the crankshaft position sensor and the ECM.
  • Excessive knock sensor system spark retard activity. Observe the scan tool Knock Retard parameter for activity greater than 0° and refer to DTC P0324-P0333, P06B6, or P06B7 for further diagnosis.
  • Electromagnetic interference on the reference circuit, which can cause a misfire condition. You can usually detect electromagnetic interference 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 may be an indication that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
  • A heated oxygen sensors (HO2S) that is contaminated from fuel, silicon, or from the incorrect use of RTV sealant. The sensors may have a white powdery coating resulting in a high, but false, signal voltage, which gives a rich exhaust indication.
  • A leaking or restricted positive crankcase ventilation system.
• Inspect the exhaust system components for the conditions listed below:
  • Physical damage or possible internal malfunction.
  • Restricted 3-way catalysts.

    For additional information, refer to Symptoms - Engine Exhaust

• Inspect the engine cooling system for the conditions listed below:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis .
  • Incorrectly operating engine cooling fans. Refer to DTC P1485-P1487 .
  • Incorrectly operating engine coolant thermostat heater. Refer to DTC P00B7, P0597-P0599, or P2181 - E41 Engine Coolant Thermostat Heater Malfunction .
  • Low engine coolant level. Refer to Cooling System Draining and Filling (GE-47716) , or Cooling System Draining and Filling (Static) .

    For additional information, refer to Symptoms - Engine Cooling .

• Inspect the engine for the mechanical conditions listed below:
  • Excessive oil in the combustion chamber or leaking valve seals
  • Incorrect cylinder compression
  • Sticking or leaking valves
  • Worn camshaft lobes
  • Incorrect valve timing
  • Broken valve springs
  • Excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner, if necessary. Follow the instructions on the can.
  • Incorrect engine parts

    For additional information, refer to Symptoms - Engine Mechanical

• If the above conditions do not address the symptom, refer to the additional symptoms tests.