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

1. Test for the following conditions:
   • The fuel system for the following:
     • Improperly connected fuel injectors. Verify that each fuel injector is connected to the proper fuel injector harness connector.
     • Incorrect fuel system operation and pressure-Refer to Fuel System Diagnosis 
     • Leaking or improperly operating fuel injectors-Refer to Fuel Injector Diagnosis (CH47976) , Fuel Injector Diagnosis (J39021 or Scan Tool) .
     • Contaminated or poor quality fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
   • 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 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 .
   • 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.
   • 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
   • 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.

   • 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 with Intake Air Temperature Sensor Replacement .
   • Improper or loose 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 system spark retard activity-Refer to DTC P0324, P0325, P0326, P0327, P0328, P0330, P0332, or P0333 .
   • The exhaust system components for the following:
     • Physical damage or possible internal failure
     • Restricted three-way catalytic converters

       For more information, refer to Symptoms - Engine Exhaust .

   • 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
   • 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 .
   • The engine for the following mechanical failures-Refer to Symptoms - Engine Mechanical (L76, L77) :
     • 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
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.