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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

  1. Test for the following conditions:
    • The fuel system for the following:
    • The ignition system for the following:
      • Spark plugs for incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection .
      • For diagnosis of coolant or oil fouled spark plugs, refer to Loss of Coolant or Symptoms - Engine Mechanical .
      • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
      • Weak spark using the J 26792  Spark Tester-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 rich or lean.
    • Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions.
      • CAUTION: Refer to Heated Oxygen and Oxygen Sensor Caution .
    • Water intrusion in the HO2S connector
      • NOTE: The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine.
    • Inspect the MAF sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Install the MAF in the proper direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement .
    • Inspect the MAF sensor connections.
    • Engine oil contaminated by fuel
    • The engine for the following mechanical failures-Refer to Symptoms - Engine Mechanical :
      • Excessive oil in the combustion chamber or leaking valve seals
      • 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
    • Vacuum hoses for splits or kinks-Verify that the routing and connections are as shown on the Vehicle Emission Control Information label.
    • Knock sensor (KS) system for excessive spark retard activity-Refer to DTC P0324, P0325, P0326, P0327, P0328, P0330, P0332, or P0333 .
    • The exhaust system components for the following:
      • Physical damage or possible internal failure
      • The three-way catalytic converters for a restriction

        For more information, 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-Refer to Crankcase Ventilation System Inspection/Diagnosis .
    • Evaporative emission (EVAP) canister purge solenoid that is stuck open
    • The engine cooling system for the following conditions:
  2. If the above conditions do not address the symptom, refer to the additional symptoms tests.
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