Navajo 4WD V6-4.0L OHV (1991)
Timing Diagram
The Electronic Distributorless Ignition System (EDIS) module, located in the right front corner of the engine compartment, is a microprocessor based
device with coil drivers which make decisions about spark timing and coil firing. The module turns the coils "ON" and "OFF" at the correct time and in
the proper sequence based on information from the variable reluctance sensor (VRS) and a pulse width modulated signal (Spark Angle Word, SAW)
generated from the EEC processor. The module receives VRS and SAW signals and produces Profile Ignition Pickup (PIP) and Ignition Diagnostic
Monitor (IDM) signals which are sent to the microprocessor in the Electronic Control Assembly (ECA) computer. The PIP signal provides base timing
and rpm information. The SAW signal contains optimum spark timing information.
IDM is a function of the EDIS module. System failure information is sent from the EDIS module to the EEC processor which stores information for
diagnostic self tests. The IDM signal is also used to drive the vehicle instrument tachometer and/or a test tachometer for diagnosis.
During some EDIS faults, the Failure Mode Effects Management (FMEM) portion of the EDIS module will maintain vehicle operation. If the module
does not receive the SAW input signal, it will fix spark timing at 10° BTDC. If the module does not receive the VRS input, synchronization cannot be
achieved and the engine will not start.
