Ford Ranger Maintaince And Repair Manual page 197

HOW TO USE THIS BOOK
Common wiring schematic for an EEC−IV distributorless ignition system
Click to enlarge
The PIP signal is sent from the ICM to the PCM, which will use the PIP signal to determine base ignition
timing and rpm calculations.
The ICM also receives the Spark Angle Word (SAW) signal from the PCM, which is used by the ICM to
calculate the proper spark timing advance. Once all of the signals are calculated, the ICM determines the
proper ON and OFF timing for the ignition coils.
The 4.0L engine utilizes one ignition coil pack, which contains three separate ignition coils. Each ignition coil
fires two spark plugs simultaneously. One of the two plugs being fired is on the compression stroke (this plug
uses most of the voltage) and the other plug is on the exhaust stroke (this plug uses very little of the voltage).
Since these two plugs are connected in series, the firing voltage of one plug is negative (with respect to
186 SYSTEM OPERATION