Symptoms Testing

Backfire, Cuts Out/Misses, Detonation/Spark Knock, 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 following conditions:
   • The fuel system for the following:
     • Correct fuel pressure-Refer to Fuel System Diagnosis 
     • Fuel injectors that are leaking or improper operation-Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2)  or Fuel Injector Diagnosis (w/CH47976) .
     • Contaminated or a poor fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
   • The ignition system for the following:
     • Spark plugs for incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection and Ignition System Specifications .
     • For diagnosis of coolant or oil fouled spark plugs, refer to Loss of Coolant or Symptoms - Engine Mechanical .
     • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may 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 (EI) System Diagnosis .
   • The operation of the transmission torque converter clutch (TCC)-The scan tool should indicate an engine speed drop when the TCC is commanded ON.
   • The operation of the A/C compressor
   • Items that can cause an engine to run rich or lean.
   • Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions.
   • Water intrusion in the HO2S connector
     NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice .
   • The cylinder deactivation system. Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .
   • Inspect the 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/Intake Air Temperature Sensor Replacement .
     IMPORTANT: 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.
   • Inspect the mass air flow (MAF) sensor connections.
   • Engine oil contaminated by fuel
   • The engine for the following mechanical failures-Refer to Symptoms - Engine Mechanical :
     • 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. Follow the instructions on the can.
     • Incorrect engine parts
   • Vacuum hoses for splits or kinks-Verify that the routing and connections are as shown on the Vehicle Emission Control Information label.
   • Knock sensor (KS) system for excessive spark retard activity-Refer to Knock Sensor (KS) System Description andDTC P0324, P0325, P0326, P0327, P0328, P0330, P0332, or P0333 .
   • The exhaust system components for the following:
     • Physical damage or possible internal failure
     • The three-way catalytic converters for a restriction

       For more information, refer to Symptoms - Engine Exhaust .

   • Electromagnetic interference (EMI) on the reference circuit 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.
   • The crankcase ventilation valve for proper operation-Refer to Crankcase Ventilation System Inspection/Diagnosis .
   • Evaporative emission (EVAP) canister purge solenoid that is stuck open
   • The engine cooling system for the following conditions:
     • The thermostat is the correct heat range. Refer to Thermostat Diagnosis .
     • Proper engine coolant level-Refer to Draining and Filling Cooling System (9C1, 9C3 Static Fill) or Draining and Filling Cooling System (LS4 GE 47716 Fill) or Draining and Filling Cooling System (LS4 Static Fill) or Draining and Filling Cooling System (LZE, LZ4, LZ8, 9C1, 9C3, GE47716 Fill) or Draining and Filling Cooling System (LZE, LZ4, LZ8 Static Fill) .
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.