K 1500 Suburban 4WD V8-393 6.5L DSL Turbo VIN S (1996)
Glow Plug: Description and Operation
Glow Plug Location
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 for a short time after starting, then are 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.
GLOW PLUG SYSTEM OPERATION
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.
CIRCUIT OPERATION
A normal functioning system operates as follows:
A. Key "ON" engine not running and at room temperature.
1. Glow plugs "ON" for 4 to 6 seconds, then "OFF" for about 4.5 seconds.
2. Then cycle "ON" for about 1.0 second, "OFF" for out 3.0 seconds, and continue to cycle 1.0 "ON," 3.0 "OFF," for a total duration (including
the initial 4 to 6 seconds) of about 16 seconds.
B. If the engine is cranked during or after the above sequence, its possible the glow p1ugs 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.
NOTE: All the times shown above are approximate, because they vary with initial engine temperature. The initial "ON" time and cycling
"ON"/OFF" times vary also, with system voltage and/or temperature. Lower temperatures cause longer duration of cycling.
GLOW PLUG AFTER START
The Powertrain Control Module (PCM) provides glow plug operation after starting a cold engine. This after start operation is initiated when the
ignition switch is returned to RUN, from the START position. While loss of this function may not cause a cold start complaint, it may result in
excessive white smoking and/or poor idle quality after start.
