Tech Tip: Ford Truck No-Start Following CKP Replacement – UnderhoodService

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Technical resources to help diagnose and repair engine-related service issues.
Electronic

Tech Tip: Ford Truck No-Start Following CKP Replacement

After replacing the Crankshaft Position Sensor (CKP) and/or connector to correct another problem, the engine turns over, but does not start. The fuel injectors pulse a couple of times when the engine starts cranking, then they stop pulsing. There is an rpm reading on the scan data for a split second, then it goes to zero. There is no spark.

Underhood Service Staff Writers
By Underhood Service Staff Writers
Published:

Vehicle: 1997-2002 Ford F-150 4.2L, 4.6L and 5.4L; and 1996 Ford F-150 5.0L

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Symptom: After replacing the Crankshaft Position Sensor (CKP) and/or connector to correct another problem, the engine turns over, but does not start.

The fuel injectors pulse a couple of times when the engine starts cranking, then they stop pulsing. There is an rpm reading on the scan data for a split second, then it goes to zero. There is no spark.  

Problem: Reversed Crankshaft Position Sensor (CKP) wiring

Test & Fix: This is the exact symptom of reversed polarity on the CKP sensor wires. It may be due to the wires being installed in the connector incorrectly during a terminal replacement, or a sensor that was installed has reversed polarity.

To Repair: At the CKP connector, remove the grey and blue wires from their respective terminals and reverse them in the connector and recheck for proper operation.

Courtesy of Identifix.

For more information, visit www.identifix.com. 

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