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

• Test/inspect the fuel system for the conditions listed below:
  • Incorrect system operation or fuel pressure.
  • Leaking or incorrectly operating fuel injectors.
  • Contaminated or poor quality fuel.
• Test/inspect the ignition system for the conditions listed below:
  • Spark plugs with incorrect heat range or an abnormal condition - Refer to 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 (Diagnostic Tools)Special Tools (Mechanical 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 Throttle Body Idle Air Flow Compensation Reset procedure must be performed when the repair is complete.
  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.

  • Incorrect installation of the Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor. If the sensor is incorrectly installed, a hard start may be the result. Install the sensor in the correct direction.
  • Incorrect operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON.
  • Incorrect operation of the A/C compressor
  • Items that can cause an engine to run lean or rich.
  • 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 - 1 200 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.
  • Incorrectly set 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. Inspect all connections for leaks or restrictions.
  • 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 .
  • An incorrectly operating engine coolant thermostat heater. Refer to DTC P00B7, P0597-P0599, P2181, or E41 Engine Coolant Thermostat Heater Malfunction .
  • Incorrect engine coolant level. Refer to Cooling System Draining and Filling .

    For additional information, refer to Symptoms - Engine Cooling .

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

    For additional information, refer to Symptoms - Engine Exhaust .

• Test/inspect the engine for the mechanical conditions listed below:
  • 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

    For additional information, refer to Symptoms - Engine Mechanical.

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