Ford Explorer, Maintaince And Repair Manual, Page: 198 / 1119

ground) and the other plug is positive.
If, for some reason, a fault arises in the EI system, the Failure Mode Effects Management (FMEM) portion of
the ICM maintains vehicle operation. If the ICM stops receiving the SAW input signal, it will directly fire the
ignition coils based on the CKP signal. This condition results in a fixed timing of 10 degrees BTDC.
EEC−V Systems
The CKP signal is sent to the PCM, which uses the signal to determine base ignition timing and rpm
calculations.
The one missing tooth on the data wheel creates one large space between two of the teeth. The PCM utilizes
this large space as a reference to help determine base ignition timing and engine speed (rpm), and to
synchronize the ignition coils for the proper spark timing sequence.
All engines, except the 2.3L, 2.5L and 5.0L engines, utilize one ignition coil pack, which contains three
separate ignition coils, whereas the 2.3L, 2.5L and 5.0L engines use two separate ignition coil packs, each of
which contains two 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 ground) and the other plug is positive.
Diagnosis and Testing
SERVICE PRECAUTIONS
Always turn the ignition key OFFand isolate both ends of a circuit whenever testing for shorts or
continuity. •
Never measure voltage or resistance directly at the processor connector.
•
Always disconnect solenoids and switches from the harness before measuring for continuity,
resistance or energizing by way of a 12−volt source. •
When disconnecting connectors, inspect for damaged or pushed−out pins, corrosion, loose wires, etc.
Service if required. •
PRELIMINARY CHECKS
Visually inspect the engine compartment to ensure that all vacuum lines and spark plug wires are
properly routed and securely connected. 1.
Examine all wiring harnesses and connectors for insulation damage, burned, overheated, loose or
broken connections. 2.
Be certain that the battery is fully charged and that all accessories are OFFduring the diagnosis. 3.
GENERAL SYSTEM TEST
This is a general system test for a no−start condition. Use the accompanying flow charts for this test. For
ignition coil testing refer to the ignition coil procedures.
Most Digital Volt Ohmmeters (DVOMs) used today belong to a class referred to as "averaging." Some
averaging DVOMs include the Rotunda® 007−00001, the Fluke® 70, 20 series and the Fluke® 88.
HOW TO USE THIS BOOK
SYSTEM OPERATION 187