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:
   • For the correct installation of the mass air flow (MAF) sensor.
   • 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 Balance Test with Special Tool .
     • 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 REPLACEMENT .
     • For diagnosis of coolant or oil fouled spark plugs, refer to 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 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. Refer to DIAGNOSTIC SYSTEM CHECK - AUTOMATIC TRANSMISSION .
   • The operation of the A/C compressor
   • Items that can cause an engine to run lean or rich-Refer to DTC P0171 or P0172 .
   • 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. Refer to EVAPORATIVE EMISSIONS HOSE ROUTING DIAGRAM .
   • Knock sensor (KS) system for excessive spark retard activity-Refer to KNOCK SENSOR REPLACEMENT and DTC P0324, P0326, or P06B6 .
   • 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.
   • Inspect the positive crankcase ventilation (PCV) system and all connections for leaks or restrictions. Refer to Crankcase Ventilation System Inspection/Diagnosis or Crankcase Ventilation System Description .
   • Evaporative emission (EVAP) canister purge solenoid that is stuck open
   • Evaporative emission (EVAP) canister vent solenoid that is stuck closed
   • 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 Cooling System Draining and Filling .
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.