See Figure 1
1997-99 Ford Escort and Mercury Tracers equipped with the 2.0L engine use an integrated electronic ignition system. The ignition system consists of a Crankshaft Position (CKP) sensor, coil pack, wiring and the Powertrain Control Module (PCM). The ignition is controlled by the PCM and is non-adjustable.
The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to the crankshaft, and sends this information to the PCM. The PCM then uses this information on when to fire the coil pack.
The coil pack, which contains two separate coils, fires two spark plugs at the same time after it receives the signal from the PCM. The spark plugs are paired so that as one plug fires during the compression stroke, the other plug fires on the exhaust stroke. The next time the coil is fired, the situation is reversed.
The PCM acts like a switch to ground in the coil primary circuit. When the switch is closed, the battery positive voltage applied to the coil primary circuit builds a magnetic field around the primary coil. When the switch opens, the power is interrupted and the primary field collapses, inducing the high voltage in the secondary coil windings, and the spark is fired through the spark plug wire from the coil to the plug. A kickback voltage spike occurs when the primary field collapses. The PCM uses this spike to generate an Ignition Diagnostic Monitor (IDM) signal. The IDM communicates information by pulse width modulation in the PCM.