Symptoms Testing

Backfire, Cuts Out/Misses, Detonation/Spark Knock, Engine Control Module (ECM) Commanded Reduced Engine Power, 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 conditions listed below:
   • Incorrectly operating fuel system. Test/inspect 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 fuel quality - Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
   • Incorrectly operating ignition system. Test/inspect for the conditions listed below:
     • 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 - Refer to Coolant in Combustion Chamber , or Oil Consumption Diagnosis .
     • Secondary ignition system susceptible to moisture. Wet down the system with water from a spray bottle to help locate damaged or deteriorated components. With the engine running, look/listen for arcing or misfiring as the water is applied.
     • Weak spark using the J 26792  HEI Spark Tester - Refer to Electronic Ignition System Diagnosis .
   • 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.
   • Incorrectly operating A/C compressor
   • Items that can cause an engine to run rich or lean.
   • 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 MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine.

   • Incorrectly installed MAF sensor. 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 .
   • Loose or incorrect MAF 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 greater than 0°. For additional information, refer to DTC P0324, P0326, P0331, P06B6, or P06B7 , DTC P0325, P0327, P0328, P0330, P0332, or P0333 .
   • 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.
   • Incorrectly operating crankcase ventilation valve - Refer to Crankcase Ventilation System Inspection/Diagnosis .
   • A stuck open evaporative emission (EVAP) canister purge solenoid.
   • Incorrectly operating engine cooling system. Test/inspect 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 (Static Fill L96)Cooling System Draining and Filling (Vac N Fill L96)Cooling System Draining and Filling (Vac N Fill L83 L86)Cooling System Draining and Filling (Static Fill L83 L86) .

       For additional information, refer to Symptoms - Engine Cooling .

   • Incorrectly operating exhaust system. Test/inspect the components for the conditions listed below:
     • Physical damage or possible internal failure
     • Restricted three-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
     • 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 additional information, refer to Symptoms - Engine Mechanical
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.