Starting System: Description and Operation

Start

The Battery, Starter Motor, Starter Relay and Ignition Switch make up the Starting System. The Starter Backup Switch or Clutch Triple Function Switch must be closed (gear shift lever in PARK or NEUTRAL or clutch pedal depressed) in order to operate the Starter Motor.

Turning the Ignition Switch to START sends current through the Starter Relay coil and operates the Relay. Current from the Battery then flows directly through the Starter Relay to the Starter Motor to start the engine.

When the Ignition Switch is in the START position, full voltage is applied to the BATT terminal of the Ignition Coil.

Electronic Distributorless Ignition System (EDIS)

In the Electronic Distributorless Ignition System (EDIS), all engine timing and spark distribution is handled electronically with no moving parts. During basic operation, the EEC IV Module determines the spark advance required by the engine and sends this information to the EDIS Module. The EDIS determines which Ignition Coil to fire and when to fire it.

The crankshaft timing sensor is Variable Reluctance (magnetic) Sensor (VRS) which is activated by a 36 minus 1 tooth wheel that is mounted on the crankshaft pulley hub assembly. The VRS signal tells the EDIS two things:

1.) The position of the crankshaft (degrees from the missing tooth).

2.) The speed (RPM) of the engine.

Initial timing (base timing) is set 10~ BTDC in the EDIS and is not adjustable.

A three coil, six tower pack is used for the 4.0L V6 engine. The three coils are turned on and off at the right time by the EDIS Module. Each Ignition Coil has two towers that fire two spark plug simultaneously, one spark plug on the compression stroke and one spark plug on the exhaust stroke. The spark plug fired on the exhaust stroke uses very little of the Ignition Coil's stored energy, and the majority of the Ignition Coil's energy is used by the spark plug fired on the compression stroke. Since these two spark plugs are connected in series, the firing voltage of one spark plug will be positive with respect to ground, while the other will be negative with respect to ground.

The main functions of the EDIS Module are to turn the correct coil on and off at the right time to produce the spark at the right time and with the right energy. The EDIS receives the crankshaft signal from the VRS and a SAW (Spark Advance Word) signal from the EEC IV Module is calling for. The EDIS Module uses the VRS and SAW signals to calculate when to perform the coil on/offs. The EDIS Module then executes all its own coil and spark functions and is not triggered by the EEC IV Module. In other words, SPOUT (spark out) signals are not used. The EDIS Module also sends a PIP (Profile Ignition Pickup) signal to the EEC IV for its use as an RPM signal. The EDIS Module uses the change in the VRS crankshaft signal caused by the missing tooth and keeps a count of the number of teeth that follow to determine where the engine is in its firing order so that the appropriate coil will be selected to fire the spark in the right sequence.

During some EDIS faults, the Failure Mode Effects Management (FMEM) portion of the EDIS Module will maintain ignition operation. If the EDIS Module does not receive the SAW signal from the EEC IV, it will begin to schedule sparks at a default timing of 10~ BTDC.

TROUBLESHOOTING STEPS
BATTERY AND CABLE CHECK

^ Check condition of Battery; recharge or replace as necessary.

^ Check Battery post and cable lugs.

^ Check cable terminals at engine ground and Starter Motor; clean and tighten as necessary. Verify that cable strands are securely attached in terminals (cables are tight when eyelets cannot be easily turned by hand).