Circuit/System Testing
- Perform the Crankshaft Position System Variation Learn
procedure. The scan tool should display Learned Successful.
- If the Crankshaft Position System Variation Learn Procedure cannot be performed successfully, inspect for the following conditions and repair as necessary:
- Worn crankshaft main bearings
- A damaged or misaligned reluctor wheel
- Excessive crankshaft runout
- A damaged crankshaft-Refer to Crankshaft and Bearing Cleaning and Inspection .
- Interference in the signal circuit of the crankshaft position sensor
- The ignition switch is in the ON position until there is insufficient system voltage.
- An ECM power disconnect with the ignition ON that may have erased the crankshaft position system variation values and set DTC P0315
- Debris between the crankshaft position sensor and the reluctor wheel
- Verify the Learn Procedure is successful.
- If the ECM is unable to complete the learn procedure, replace the ECM.
- Verify that the following conditions do not exist:
- Vacuum hose splits, kinks, and incorrect connections
- Engine vacuum leaks
- Crankcase ventilation system for vacuum leaks
- Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis .
- Contaminated fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Exhaust system restrictions
- If you find any of the above conditions, repair as necessary.
- Ignition OFF, remove the T8 ignition coil of the misfiring cylinder, but leave the electrical connector connected.
- Inspect the ignition coil boot for the following conditions:
- Holes
- Tears
- Carbon tracking
- Oil contamination
- Water intrusion
- If you find any of the above conditions, repair as necessary.
- Install the J 26792 to the boot of the appropriate T8 ignition coil and ground.
- Attempt to start the engine and observe the J 26792
. The spark tester should spark.
- If there is no spark, refer to Electronic Ignition System Diagnosis for diagnosis of the ignition coil.
- Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the spark plug does not exhibit the following conditions:
- Gas, coolant, or oil fouled-Refer to Spark Plug Inspection .
- Cracked, worn, incorrectly gapped-Refer to Ignition System Specifications .
- If there is a condition with the spark plug, replace the spark plug.
- Exchange the suspected spark plug with another cylinder that is operating correctly.
- Operate the engine under the conditions in which the misfire occurred. Observe the Misfire Current Cyl. 1-4 parameters with a scan tool. The misfire should not follow the spark plug exchange.
- If the misfire follows the spark plug, replace the spark plug.
- If all conditions test normal, test or inspect for the following:
- A lean or rich Q17 fuel injector-Refer to Fuel Injector Solenoid Coil Test .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical .
NOTE:
An erratic or weak spark is considered a no spark condition.