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 the fuel system for the following:
  • 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 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 J-26792  Spark Tester - Refer to Electronic Ignition System Diagnosis .
• Inspect for the following conditions:
  • 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.
  • Incorrectly operating 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 for more information.
  • Slow responding heated oxygen sensors (HO2S) - The HO2S should respond quickly to different throttle positions - Refer to DTC P0133, P013A, P013B, P013E, P013F, P015A, P015B, P2270, or P2271 for more information.
  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 mass air flow sensor installation. A mass air flow sensor that is incorrectly installed may cause a hard start. Install the mass air flow in the proper direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement .
  • Incorrect mass air flow sensor connections.
  • Engine oil contaminated by fuel
  • Split or kinked vacuum hoses - Verify that the routing and connections are correct.
  • Excessive knock sensor system spark retard activity - Observe the Knock Retard parameter on the scan tool for activity more than 0°.
  • Electromagnetic interference (EMI) 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 crankshaft position sensor with an intermittent condition - Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter parameter should not increment 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.
  • Incorrectly operating crankcase ventilation valve - Refer to Crankcase Ventilation System Inspection/Diagnosis .
• Inspect the engine cooling system for the following conditions:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis .
  • Incorrect engine coolant level - If the level is low, refer to Loss of Coolant .

    For more information, refer to Symptoms - Engine Cooling .

• Inspect the exhaust system components for the following conditions:
  • Physical damage or possible internal failure
  • Restricted three-way catalytic converters

    For more information, refer to Symptoms - Engine Exhaust .

• Inspect the engine for the following mechanical conditions:

  Refer to Symptoms - Engine Mechanical .

  • 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
• If the above conditions do not address the symptom, refer to the Additional Symptoms Tests.