Symptoms Testing

Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Engine Control Module (ECM) Commanded Reduced Engine Power, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles

1. Test for the following conditions:
   • For the correct installation of the Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor.
   • The fuel system for the following:
     • Correct fuel pressure. Refer to Fuel System Diagnosis .
     • Leaking or incorrectly operating fuel injectors. Refer to Fuel Injector Diagnosis .
     • Contaminated or a poor fuel quality condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
   • The ignition system for the following:
     • Spark plugs with incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection , and Ignition System Specifications .
     • Coolant or oil fouled spark plugs-For diagnosis, refer to Coolant in Combustion Chamber , or Oil Consumption Diagnosis .
     • Secondary ignition system susceptible to moisture. Engine running, wet down the secondary ignition system with water from a spray bottle to help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
     • Weak spark using the EL 26792  HEI Spark Tester. For equivalent regional tools, refer to Special Tools , . Refer to Electronic Ignition System Diagnosis .
   • The operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON.
   • The operation of the A/C compressor
   • Items that can cause an engine to run lean or rich. Refer to DTC P0171 or P0172 .
   • The crankshaft position sensor for the correct resistance. The crankshaft position sensor resistance may be out of range after a hot soak. The resistance should be between 700-1 200 Ω.
   • The engine for the following mechanical failures. Refer to Symptoms - Engine Mechanical .
     • Too much 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
     • Too much carbon buildup in the combustion chambers. Clean the chambers with top engine cleaner, if necessary. Follow the instructions on the can.
     • Incorrect engine parts
   NOTE:

   The embossed arrows on the mass air flow (MAF) sensor indicate the direction of the intake air flow. The arrows must point toward the engine.

   • Improper MAF sensor installation. A mass air flow sensor that is improperly installed may cause a hard start. Install the mass air flow in the proper direction. Refer to Mass Airflow Sensor Replacement .
   • Vacuum hoses for splits or kinks. Verify that the routing and connections are as shown on the vehicle emission control information label.
   • Knock sensor system for too much spark retard activity. Refer to Knock Sensor Replacement , and DTC P0335 or P0336 .
   • Fuel octane switch setting, if equipped. Verify the fuel octane switch is set to the proper fuel octane rating for the fuel being used in the vehicle.
   • The exhaust system components for the following:
     • Physical damage or possible internal malfunction
     • The 3-way catalytic converters for a restriction

       For more information, refer to Symptoms - Engine Exhaust .

   • Electromagnetic interference on the reference circuit 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 indicates that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
   • Inspect the positive crankcase ventilation system and all connections for leaks or restrictions.
   • Evaporative Emission (EVAP) Canister Purge Solenoid Valve that is stuck open
   • The engine cooling system for the following conditions:
     • The thermostat is the correct heat range. Refer to Thermostat Diagnosis .
     • The engine coolant thermostat heater is working proper. Refer to DTC P0597-P0599 .
     • Proper engine coolant level. Refer to Cooling System Draining and Filling .
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.