See Figure 1
1991-96 Ford Escort and Mercury Tracer models equipped with the 1.9L engine use a high data rate Electronic Distributorless Ignition System (EDIS). This ignition system is controlled by an EDIS ignition control module and the Powertrain Control Module (PCM) operating in union. The system is designed to deliver a full energy spark at a crank angle selected by the PCM. This system is a modified version of the Distributorless Ignition System (DIS). The EDIS consists of a Crankshaft Position (CKP) sensor, an EDIS ignition control module, PCM and a coil pack.
The CKP sensor is a variable reluctance type sensor triggered by a 36-minus-1 trigger wheel configuration pressed onto the rear of the crankshaft damper. The signal generated by this sensor provides engine position rpm to the ignition control module.
The EDIS ignition control module receives the information on engine position and rpm from the CKP sensor and desired spark advance from the PCM. The module then uses this information to direct which coil to activate, as well as to calculate the TURN ON and TURN OFF times of the coils required to achieve the correct dwell and spark advance. The module also generates a Profile Ignition Pick-up (PIP) signal and an Ignition Diagnostic Monitor (IDM) signal for use by the PCM. The module signals the PCM of signal failures through the IDM. The PCM then stores this information as trouble codes. A Clean Tach Output (CTO) signal is also provided to drive the tachometer.
The ignition coil pack contains two separate ignition coils which are controlled by the EDIS module through two ignition coil leads. Each coil activates sparks plugs at two cylinders simultaneously. While one plug is active on the compression stroke, the companion plug is active on the exhaust stroke. At the next engine revolution, this process will reverse. The plug that activates on the exhaust stroke uses very little of the coil's stored energy. The majority of the coil's energy is used by the plug active on the compression stroke. Because these two plugs are connected in series, the firing voltage of one plug is negative with respect to ground, and the other plug is positive with respect to ground.