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 the fuel system for the following:
  • Correct fuel system operation and pressure-Refer to Fuel System Diagnosis (Without FPCM) , Fuel System Diagnosis (FPCM) 
  • Fuel injectors incorrectly connected. Verify each injector is connected to the correct fuel injector harness connector.
  • Improperly operating or leaking fuel injectors-Refer to Fuel Injector Diagnosis (CH47976) , Fuel Injector Diagnosis (J39021 or Scan Tool) .
  • Poor fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Test the ignition system for the following conditions:
  • 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 water. 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:
  • Improperly operating transmission torque converter clutch (TCC)-The scan tool should indicate an engine speed drop when the TCC is commanded ON.
  • Improperly 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 P0133, P013A-P013F, P014A, P014B, P0153, P1133, or P1153 (LC9, LMG, L96) , or DTC P0133, P013A-P013F, P014A, P014B, P0153, P015A, P015B, P015C, or P015D (L9H, L94) for more information.
  CAUTION:

  Refer to Heated Oxygen and Oxygen Sensor Caution .

  • Water intrusion in the HO2S connector
  • Improperly operating cylinder deactivation system, if equipped. Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .
  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.

  • Improper 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 with Intake Air Temperature Sensor Replacement .
  • Improper 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 (KS) system spark retard activity-Refer to DTC P0324, P0325, P0326, 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.
  • Improperly operating crankcase ventilation valve-Refer to Crankcase Ventilation System Inspection/Diagnosis .
  • A stuck open evaporative emission (EVAP) canister purge solenoid.
• 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 cooling system for the following conditions:
  • A thermostat with incorrect heat range. Refer to Thermostat Diagnosis .
  • Improper engine coolant level-Refer to Cooling System Draining and Filling (Static Fill) .
• 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 more information, refer to Symptoms - Engine Mechanical .

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