Symptoms Testing

Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Engine Control Module (ECM) Commanded Reduced Engine Power, Fuel Odor, 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 following:
  • 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 .
• Test/inspect the ignition system for the following conditions:
  • Spark plugs with incorrect heat range or an abnormal condition - Refer to Gas Engine Ignition 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. 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 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.
  • Incorrectly operating A/C compressor
  • Items that can cause an engine to run rich or lean - Refer to DTC P0171, P0172, P0174, or P0175 for more information.
  • Slow responding heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions - Refer to DTC P0137, P0138, P013A-P013F, P014A, P014B, P0157, P0158, or P2270-P2273 for more information.
  CAUTION:

  Refer to Heated Oxygen and Oxygen Sensor Caution .

  • Water intrusion in the HO2S connector
  • Incorrectly operating cylinder deactivation system, if equipped. Refer to Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing .
  NOTE:

  The embossed arrows on the mass airflow (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. Refer to Mass Airflow Sensor Replacement .
  • Incorrect MAF sensor connections.
  • A MAF sensor contaminated by an excessively oiled aftermarket air filter. Some aftermarket air filters require oil to be added to the air filter element. If the MAF sensor becomes contaminated as the result of an excessively oiled aftermarket air filter, a variety of driveability concerns and/or erratic transmission shifting may occur.
  • 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 more 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.
  • A crankshaft position sensor with an intermittent condition - Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter parameter should remain at 0 counts during all operating conditions, and when moving the related harnesses and connectors between the crankshaft position sensor and the ECM.
  • Incorrectly operating crankcase ventilation valve - Refer to Crankcase Ventilation System Inspection/Diagnosis .
  • A stuck open evaporative emission (EVAP) canister purge solenoid - Refer to Evaporative Emission Control System Description .
• Test/inspect the engine cooling system for the following conditions:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis .
  • Incorrect engine coolant level - Refer to Cooling System Draining and Filling (LT4 Static Fill) , or Cooling System Draining and Filling (LT4 GE 47716) .

    For additional information, refer to Symptoms - Engine Cooling .

• Test/inspect the exhaust system components for the following conditions:
  • 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 following mechanical conditions:
  • 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 .

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