Symptoms Testing

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

• Test/inspect the fuel system for the conditions listed below:
  • Incorrect system operation or fuel pressure - Refer to Fuel System Diagnosis (LUV) .
  • 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:
  • Spark plugs with incorrect heat range or an abnormal condition - For diagnosis, refer to Spark Plug Inspection , and Ignition System Specifications .
  • Coolant or oil fouled spark plugs - Refer to Oil Consumption Diagnosis , and Loss of Coolant .
  • 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 (Diagnostic Tools) , . Refer to Electronic Ignition System Diagnosis .
• 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.
  • Incorrectly operating turbocharger system. Inspect the turbocharger charge air cooler system for leaks and refer to:
    • Turbocharger Cleaning and Inspection
    • Turbocharger System Description
  • Incorrectly operating transmission torque converter clutch (TCC) - The scan tool should indicate an engine speed drop when the TCC is commanded ON.
  • Incorrectly operating A/C compressor
  • Items that can cause an engine to run lean or rich - Refer to DTC P0171 or P0172 .
  • Incorrectly installed Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor.
  • Incorrect MAF/IAT sensor connections.
  • A MAF sensor contaminated by an excessively oiled aftermarket air filter. Some aftermarket air filters require oil to be added to the air filter element. If the MAF sensor becomes contaminated as the result of an excessively oiled aftermarket air filter, a variety of driveability concerns and/or erratic transmission shifting may occur.
  • Incorrect crankshaft position sensor resistance - The crankshaft position sensor resistance may be out of range after a hot soak. The resistance should be between 700 - 1200 Ω.
  • Split or kinked vacuum hoses - Verify that the routing and connections are as shown on the vehicle emission control information label.
  • Excessive knock sensor system spark retard activity or faulty operation - Refer to Knock Sensor Replacement , DTC P0325, P0327, or P0328 , and DTC P0324, P0326, or P06B6  .
  • Incorrect 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.
  • 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 indicates that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
  • A leaking or restricted positive crankcase ventilation system.
  • A stuck open Evaporative Emission (EVAP) Canister Purge Solenoid Valve.
• Test/inspect the engine cooling system for the conditions listed below:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis .
  • Incorrect engine coolant level - Refer to Cooling System Draining and Filling .
  • Incorrectly operating engine coolant thermostat heater. Refer to DTC P0597-P0599 (2H0 or LUJ)

    For additional information, refer to Symptoms - Engine Cooling .

• Test/inspect the exhaust system components for the conditions listed below:
  • Physical damage or possible internal failure
  • Restricted 3-way catalytic converters

    For additional information, refer to Symptoms - Engine Exhaust .

• Test/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.