Diagnosis; On-Vehicle Service - GMC G Service Manual

B. If the engine is cranked during or after the above
sequence, the glow plugs will cycle "ON/OFF" for a
total duration of 25 seconds 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.
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 glow plug controller provides glow plug operation
after starting a cold engine. This after start operation is
initiated when the engine control switch is returned to RUN,
from the START position. While loss of this function may
not cause a start complaint, it may result in excessive white
smoking and/or poor idle quality after start. To check for
proper operation of this circuit, proceed as follows:
1. With the engine cold, 27 degrees C (80 degrees F),
turn the engine control switch to the RUN position and
let the glow plugs cycle.
2. After 2 minutes, crank the engine for 1 seconds. (It is
not important that the engine start). Return the engine
control switch to RUN. Glow plugs should cycle at
least once after cranking.
3. If the glow plugs do not turn "ON", disconnect the
controller connector, and probe harness connector
terminal "B" with a test light connected to ground. The
light should be "OFF", with the engine control switch
in RUN and "ON", when the engine is cranked.
4. If the light does not operate as just described, repair a
short or open in the engine harness purple wire.
5. If the light works rights, but the after start glow plug
feature does not, replace the converter.

DIAGNOSIS

CIRCUIT CHECK
If the system does not operate as described in Circuit
Operation, check the following:
DIESEL EMISSIONS 6E2-59
09
Inspect
1. All connectors.
2. Engine harness ground connection to engine.
H O Tighten
• Nut to 11 N»m (96 in. lbs.).
3. Four-wire connector at controller. It must be fully
seated and latched.
4. Both controller copper stud upper nuts.
Tighten
• Nuts to 5 N»m (48 in. lbs.).
• Do not tighten lower nuts.
5. Glow plug lamp on instrument panel for tight connec­
tion and operation.
If all connections are intact, but the glow plug system
does not operate as stated, perform the Glow Plug Circuit
Electrical Check. If provides a fast way to determine if the
glow plug system is working properly. Use this procedure,
whenever there is doubt about correct system operation.
NOTICE: Do not manually bypass the relay In the
glow plug controller. Do not jump start with
more than a 12 volt system. The glow plugs
could be damaged.

ON-VEHICLE SERVICE

Check the system and its components on the vehicle.
None of the components are repairable. The glow plugs,
controller and coolant sensor may be replaced. Refer to
ENGINE ELECTRICAL (SEC. 6D). When installing new
components and making connections, be sure that connec­
tions are tight and torque values are used. Torque the glow
plugs to 17 N*m (12 ft. lbs.), when installed.