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. 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:
  • Spark plugs with an 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. 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 J-26792  Spark Tester. 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 Throttle Body Idle Air Flow Compensation Reset procedure must be performed when the repair is complete.
  • On vehicles equipped with automatic transmission, incorrect operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis .
  • Incorrectly operating A/C compressor.
  • An engine that runs lean or rich. Observe the Fuel Trim parameters with a scan tool. Refer to DTC P0171 or P0172 .
  • Slow responding 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 mass air flow (MAF) sensor indicate the direction of the intake air flow. The arrows must point toward the engine.

  • Incorrect MAF sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Install the MAF in the proper direction.
  • Incorrect mass air flow (MAF) sensor connections.
  • Engine oil contaminated by fuel
  • 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 - Observe the Knock Retard parameter on the scan tool for activity greater than 0°. Refer to DTC P0324-P0333, P06B6, or P06B7 , and Knock Sensor Replacement for additional information.
  • Electromagnetic interference (EMI) on the reference circuit, which 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.
  • A crankshaft position sensor with an intermittent condition, observe the scan tool Crankshaft Position Resync parameter. The Resync 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.
  • A stuck open evaporative emission (EVAP) canister purge solenoid.
• 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. If the level is low, refer to Loss of Coolant .
• Test/Inspect the exhaust system components for the conditions listed below:
  • Physical damage or possible internal failure
  • Restricted 3-way catalytic converters.

    For more 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
  • Oil Consumption
  • 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, if necessary. Follow the instructions on the can.
  • Incorrect engine parts

    For more information, refer to Symptoms - Engine Mechanical .

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