In the diesel engine, air alone is compressed in the cylinder. After the air has been compressed, a charge of fuel is sprayed into the cylinder and then the ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the Glow Plugs has been accomplished by moving the logic for controlling the heat of the plugs to the PCM. The new logic can incorporate the higher accuracy of digital processing compared to the previous analog controller. Additionally, logic involving engine speed and estimates of engine combustion can be added to the traditional time and temperature data used in the previous controller. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability.

A normal functioning system operates as follows:

The Glow plug initial ON times may range from 1 to 16 seconds and the cycling ON/OFF times may vary also with the system voltage and/or temperature. The lower temperature causes longer durations of cycling.

The PCM provides the glow plug operation after starting a cold engine. This after glow operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up any excessive white smoke and/or poor idle quality after starting.

These are 6-volt heaters (operated at 12 volts) that turn ON, when the ignition switch is turned to the run position, prior to starting the engine. The 6-volt heaters remain pulsating for a short time after starting, and are then turned OFF.

A Wait to Start lamp, which is on the instrument panel, provides information pertaining to the engine starting conditions. The Wait to Start lamp will not come ON during the post glows.

The glow plug relay is mounted at the rear of the right cylinder head, which is a solid state device that operates the glow plugs.

The PCM uses an ignition voltage signal in order to control the solid state circuitry of the glow plug relay.

Glow Plug System Description MFI

The electronic controller/glow plug relay assembly contains the circuit which monitors and controls glow plug relay operation. Information received at pin B and pin C is used by the controller in order to determine the glow plug operating requirements. Pin B senses voltage at the starting motor solenoid, Pin C senses glow plug voltage. The controller also senses ambient temperature.

The relay is an integral part of the controller. The controller is mounted at the rear of the left cylinder head on two 10 mm studs.

Important: The times shown below are approximate because the initial engine temperature will affect the times. The initial ON time and the cycling ON and OFF times vary with the system voltage and the temperature. Lower temperatures cause longer duration of cycling.

A normally functioning system operates as described in the steps below:

1. Ensure the engine is at room temperature.
2. Turn the ignition switch ON, leaving the engine OFF.
3. The glow plugs will automatically cycle in the following order (steps 3.3 and 3.4 will continue to cycle until the total cycle has been in effect for 20 seconds):

3.1.	The glow plugs will be turned ON for 4 to 6 seconds.

3.2.	The glow plugs will be turned OFF for 4.5 seconds.

3.3.	The glow plugs will be turned ON for about 1.5 seconds.

3.4.	The glow plugs will be turned OFF for about 4.5 seconds.

4. If the engine is cranked during or after the above sequence, the glow plugs will cycle ON and OFF for a total of 25 seconds after the ignition switch is returned from the crank position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

In the diesel engine, only air is compressed in the cylinder. After the air has been compressed, fuel is sprayed into the cylinder, where ignition occurs due to the heat of compression. Eight glow plugs are used to preheat the chamber as an aid to starting.

The (TCM) receives temperature information from the coolant temperature sensor. The computer sends a voltage signal to the cold advance relay and the ignition circuit to the glow plug controller. The cold advance relay is located at the junction block in the engine compartment on the right side of the cowl.

Glow plugs are 6-volt heaters which are operated at 12 volts. Glow plugs are turned ON when the ignition switch is turned to the RUN position prior to starting the engine. The glow plugs remain pulsing a short time after the engine is started. The glow plugs are automatically turned OFF.

Vehicles with the diesel engine have special instrumentation indicators to permit the operator to properly apply the starting procedure. A GLOW PLUGS lamp on the instrument panel provides the information regarding engine starting conditions.

Vehicles equipped with diesel engines have a WATER IN FUEL lamp and a LOW COOLANT lamp. Refer to Engine Cooling.