In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.
Control of the glow plugs is accomplished by moving the logic for controlling the heat of the plugs to the engine control module (ECM). 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:
| • | Turn the ignition ON with the engine OFF, and at room temperature. |
| • | The glow plugs turn ON for between 1 and 16 seconds. |
| • | If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and 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 time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.
The ECM provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.
Glow Plugs
The glow plugs are heaters in each of the cylinders that turn ON when the ignition switch is turned to the Run position prior to starting the engine. They remain pulsing a short time after starting, then they are turned OFF.
A Wait to Start lamp on the instrument panel provides information on engine starting conditions. The Wait to Start lamp will not illuminate during post-start glow plug operation.
Glow Plug Relay/Controller
The glow plug relay is a solid state device which operates the glow plugs on Federal Emissions Vehicles. The glow plug controller is a solid state device which operates the glow plugs on California Emissions vehicles. Both components perform the same function of turning ON the glow plugs based on ECM commands
The glow plug controller or relay is connected to the following circuits:
| • | The fuel heater ignition 1 voltage circuit |
| • | The battery voltage circuit |
| • | The glow plug enable circuit located between the ECM and the glow plug relay or controller |
| • | The engine ground circuit |
| • | The glow plug supply voltage circuit located between the glow plug relay/controller and the glow plugs. |
On the California Emissions vehicles, the glow plug diagnostic circuit connects directly from the ECM to the glow plug controller. On Federal emissions vehicles, the glow plug diagnostic circuit is spliced to the glow plug enable circuit after the relay.
