System Description

EEC-IV ELECTRONIC DISTRIBUTORLESS IGNITION SYSTEM (EDIS)







Components

The EEC-IV Electronic Distributorless Ignition System (EDIS) for the 4.0L engine consists of the following components:

- Crankshaft timing sensor and 36-1 tooth trigger wheel
- EDIS Ignition Module
- Ignition coil pack
- EEC-IV module
- Related wiring

Crankshaft Timing Sensor






The crankshaft timing sensor is a variable reluctance-type sensor, triggered by a 36 minus 1 tooth trigger wheel configuration machined into the rear of the crankshaft damper. The signal generated by this sensor is called a Variable Reluctance Sensor signal (VRS). The VRS signal provides the base timing and RPM information to the EDIS module. Base timing is set at 10 degrees BTDC and is not adjustable.

EDIS Module






The EDIS module receives the VRS signal from the crankshaft sensor and the SAW (Spark Advance Word) signal from the EEC-IV module. During normal operation, PIP is sent to the EEC-IV module from the EDIS module and provides base timing and RPM information. The VRS signal provides the EDIS module with the information required to synchronize the ignition coils so that they are fired in the proper sequence. The SAW signal is a pulse width modulated signal and contains the optimum spark timing information. The spark angle is determined by the EDIS module using a zero excess dwell control routine.

Ignition Coil Pack






The ignition coil pack contains three separate ignition coils which are controlled by the EDIS module through three coil leads. Each ignition coil fires two spark plugs simultaneously; one plug on the compression stroke and one on the exhaust stroke. The spark plug fired on stored energy. The majority of the energy is used by the spark plug on the compression stroke. Since these two spark plugs are connected in series, the firing voltage of one plug will be negative with respect to ground, while the voltage of the other will be positive with respect to ground.

Electronic Diagnostic Monitor (EDM)

The Electronic Diagnostic Monitor (EDM) is a function of the EDIS module. The EDIS module sends information on system failures to the EEC-IV, which stores the information for diagnostic self tests. The EDM signal is also used to drive the vehicle instrument tachometer and.or test tachometer for diagnosis.

Failure Mode Effects Management

During some EDIS faults, the failure mode effects management (FMEM) portion of the EDIS ignition module will maintain vehicle operation. If the EDIS module does not receive the SAW input, it will automatically turn the ignition coils on and off using the PIP signal. However, this condition will result in fixed spark timing (10 degrees BTDC). If the EDIS module does not receive the VRS input, the vehicle will not start.