Ford Taurus/Sable 1996-1999 Repair Guide

General Information


The Electronic Ignition (EI) system is used on the 3.4 DOHC engines. The system consists of the following components:

Crankshaft Position (CKP) sensor
Camshaft Position (CMP) sensor
Coil-on-plug units
Spark control portion of the Powertrain Control Module (PCM)
Related wiring

The Crankshaft Position (CKP) sensor is a variable reluctance sensor triggered by a 36 minus 1 tooth trigger wheel located inside the engine front cover. The sine wave signal generated from the CKP sensor is know as the CKP sensor signal. This signal provides two types of information to the Powertrain Control Module (PCM), the position of the crankshaft in 10 degree increments and crankshaft speed (rpm).

The Camshaft Position (CMP) sensor is a variable reluctance sensor. The sensor is triggered by the high point mark on the left hand exhaust camshaft. The CMP sensor provides camshaft rotational location to the Powertrain Control Module (PCM).

The PCM uses the CMP sensor signal for the ignition coil firing sequence and also uses the CKP sensor signal for fuel injector synchronization.

The 3.4L engine uses eight separate coil-on-plug units. Each coil-on-plug unit is controlled by the PCM. Each coil-per-plug unit is mounted directly above each spark plug and activates its own spark plug in the proper sequence as controlled by the PCM.

During some ignition system concerns the failure mode effects management portion of the PCM will maintain vehicle operation as follows:

If the spark plug output signal is interrupted, the PCM will automatically turn the coil-on-plug unit on and off using the CKP sensor signal input. This will result in a fixed-spark timing and fixed time dwell.
If the PCM does not receive the CMP sensor input during engine cranking, the PCM will revert to the double coil fire mode. One coil will fire on the compression stroke while its cylinder pair fires on the exhaust stroke. The engine will start normally.
If the PCM loses CMP input while the engine is running, the PCM will retain the proper firing sequence and will continue to fire the coil-per-plug units to maintain engine operation.