Symptoms Testing

Backfire, Cuts Out/Misses, Detonation/Spark Knock, Engine Control Module (ECM) Commanded Reduced Engine Power, Fuel Odor, Hard Start, Hesitation/Sag/Stumble, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles

1. Test/inspect 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 .
     • Fuel injectors leaking due to split or torn O-rings. With this condition, the engine may need to be cranked for an extended period of time before it will start. The smell of unburned fuel may also be present. Look for evidence of fuel injector leakage on the engine cylinder head and nearby components. Refer to Fuel Rail and Injectors Cleaning and Inspection if a leak is suspected.
     • Incorrectly operating fuel injectors - Refer to Fuel Injector Diagnosis .
     • Contaminated or poor quality fuel - 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. For diagnosis, refer to Coolant in Combustion Chamber , and Oil Consumption Diagnosis .
     • Secondary ignition system susceptible to moisture. Wet down the secondary ignition system 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 .
   • 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), if equipped with automatic transmission. 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.
   • Items that can cause an engine to run rich or lean. Refer to DTC P0171, P0172, P0174, or P0175 .
   • Slow responding heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. Refer to DTC P0131, P0132, P0137, P0138, P0151, P0152, P0157, or P0158 , and Refer to DTC P0133, P013A-P013F, P014A, P014B, P0153, P015A-P015D, P1133, P1153, or P2270-P2273 .
   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.

   • 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 Replacement .
   • Incorrect mass air flow (MAF) sensor connections. Refer to Mass Airflow Sensor Replacement .
   • 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 (KS) system spark retard activity - Observe the Knock Retard parameter on the scan tool for activity greater than 0°. Refer to DTC P0324-P0328, P0330-P0333, P06B6, or P06B7 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.
   • Incorrectly operating crankcase ventilation system - Refer to Crankcase Ventilation System Inspection/Diagnosis .
   • A stuck open evaporative emission (EVAP) canister purge solenoid. Refer to Evaporative Emission System Diagnosis .
   • 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 LWN) , or Cooling System Draining and Filling (GE 47716 LWN) , or Cooling System Draining and Filling (Static LC8, LV1, L96) , or Cooling System Draining and Filling (GE47716 LC8, LV1, L96) .

       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. Refer to Restricted Exhaust .

       For more information, refer to Symptoms - Engine Exhaust .

   • An engine mechanical condition. Test/Inspect for the 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.