Glow Plug System Description

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 engine starting.

Control of the glow plugs was accomplished by moving the logic that controls the heat of the plugs to the powertrain control module (PCM). The new logic utilizes the greater 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 keeping pre-glow times to a minimum for short wait to crank times and maximum glow plug durability.

A normal functioning system operates as follows:
^ Ignition ON, engine not running and at room temperature
^ Glow plugs ON briefly, approximate on times may range from 1-16 seconds
^ If the engine is cranked during or after the above sequence, the glow plugs may possibly cycle ON/OFF after the engine control 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.

The Glow plug initial ON times can range from 1-16 seconds and the cycling ON/OFF times can also vary with the system voltage and/or temperature. Lower temperatures cause longer durations of cycling.

The PCM provides for 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.

Glow Plugs
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 on the instrument panel provides information about the engine starting conditions. The wait to start lamp will not come ON during the post glows.

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

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