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:
   • Incorrectly operating fuel system. Test/inspect for the following:
     • Incorrect system operation or fuel pressure. Refer to Fuel System Diagnosis .
     • Leaking or 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 following:
     • Spark plugs with incorrect heat range or an abnormal condition. Refer to Ignition System Specifications .
     • Coolant or oil fouled spark plugs. For diagnosis, refer to Oil Consumption Diagnosis , and Coolant in Combustion Chamber .
     • 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 EL-26792  HEI Spark Tester. For equivalent regional tools, refer to Special Tools (Diagnostic) , or Special Tools (Mechanical) . 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.
   • An incorrectly installed MAF/Intake Air Temperature (IAT) Sensor. Refer to Mass Airflow Sensor Replacement .
   • An incorrectly operating transmission Torque Converter Clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON.
   • An incorrectly operating A/C compressor
   • Items that can cause an engine to run lean or rich. Refer to DTC P0171 or P0172 .
   • 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-P0333, P06B6, or P06B7 , and Knock Sensor Replacement (Position 1) , or Knock Sensor Replacement (Position 2) .
   • An incorrectly operating turbocharger system, if equipped.
   • Leaking turbocharger charge air cooler system, if equipped.
   • Electromagnetic interference on the reference circuit, which can cause a misfire condition. You can usually detect electromagnetic interference 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 electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
   • An incorrectly operating positive crankcase ventilation system. Inspect all connections for leaks or restrictions. Refer to Crankcase Ventilation System Inspection/Diagnosis
   • A stuck open Evaporative Emission (EVAP) Canister Purge Solenoid Valve.
   • An incorrectly operating variable camshaft actuator system. Engine warm and idling, command the intake and exhaust camshaft actuators from 0 degrees to 20 degrees and back to zero while observing the scan tool Intake Camshaft Position Variance and Exhaust Camshaft Position Variance parameters. Each parameter should be less than 2 degrees in each of the commanded states.
     • If any of the parameters is greater than 2 degrees, inspect the suspect camshaft actuator and camshaft actuator solenoid valve and valve bore for contamination, obstruction, and damage. Refer to Camshaft Actuator System Description , Camshaft Position Actuator Valve Solenoid Replacement - Intake , and Camshaft Position Actuator Valve Solenoid Replacement - Exhaust .
   • An incorrectly operating engine cooling system. Test/Inspect for the following:
     • Electronic cooling system operation. Refer to Cooling System Description and Operation (LSY, L3B) .
     • Incorrect engine coolant level. Refer to Cooling System Draining and Filling (LSY GE 47716) , or Cooling System Draining and Filling (LSY Static Fill) , or Cooling System Draining and Filling (LSY with V03 Static Fill) , or Cooling System Draining and Filling (L3B Static Fill) , or Cooling System Draining and Filling (L3B GE 47716) , or Cooling System Draining and Filling (LSY with V03 GE 47716) , or Cooling System Draining and Filling (LF4 Static Fill) , or Cooling System Draining and Filling (LF4 GE 47716) .
   • An incorrectly operating exhaust system. Test/Inspect the components for the following:
     • Physical damage or possible internal malfunction.
     • Restricted 3-way catalytic converters.

       For more information, refer to Symptoms - Engine Exhaust .

   • An engine mechanical condition. Test/Inspect for the following:
     • Too much oil in the combustion chamber or leaking valve seals
     • Incorrect cylinder compression
     • Sticking or leaking valves
     • Worn camshaft lobes
     • Incorrect valve timing
     • Broken valve springs
     • Too much 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.