GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 2WD 🢒 Engine 🢒 Engine Controls - 6.5L 🢒 Glow Plug System Description

Object Number: 26778 Size: SH
(1)Glow Plug
(2)Fuel Injector
(3)Cylinder Head
(4)Pre-Combustion Chamber
(5)Heated Sheath

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 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:

    • Key ON, engine not running and at room temperature.
    • Glow plugs ON for a short period of time (approximate on times may range from 1 to 16 seconds).
    •  If the engine is cranked during or after the above sequence, its possible the glow plugs will 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 may range from 1 to 16 seconds and cycling ON/OFF times vary also with system voltage and/or temperature. Lower temperature causes longer duration of cycling.

The PCM provides 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 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. They remain pulsing a short time after starting, then 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 come ON during post glows.

Glow Plug Relay

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

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