Glow plug wiring

[RonVan]

To the Gurus;

1990 Chevy 1/2ton suburban......6.2....stock glow controller.
There seems to be a short in the wiring and before i start chasing looms........is there a complete chassis wiring diagrams for this model?.......Please help!!!....Here is the story.
New ignition switch........new glow plugs
All wiring disconnect from controller including....
#1 - power from alternator(battery)
#2 - glow plug wire (both banks)
#3 - Mating connector (ignition switch)
#4 - glow plug "wait" light
Connect test light clip to (#1) battery (positive) and touch to (#2) shows connection~light lights up (ignition both off and on)
Connect test light clip to (#1) battery (positive) and touch to each female (A-E) of (#3)~light lights up (ignition both off and on)
Connect test light clip to (#1) battery (positive) and touch to (#2) glow plug wire~light lights up (ignition both off and on)
Connect test light clip to ignition on (positive) and touch to (#4) glow plug wait light~light lights up
Is there another relay somewhere????

[john8662]

Umm, what's the symptom here? I do see your troubleshooting.

There is another piece to the glow system on 88-91's, it's a relay on the firewall that the PCM triggers to turn on, based on the ECT sensor on the water crossover.

[RonVan]

OK John...........A little greek to me. PMC???? ECT sensor???

[john8662]

PCM = Powertrain Control Module, in short the computer, yes your 1990 has one.

ECT = Engine Coolant Temperature, it's a sensor mounted in the water crossover (thermostat housing) that reports to the computer what the temperature is. This sensor is separate from the one that runs the gauge inside the cab.



Here is the other relay that works in conjunction with the computer, and the glow plug controller. This relay simply "turns on" one of the pins on the controller and allows the controller to function. The glow controller itself is still self-regulated, and will come on if the temperature falls below a certain threshold, and won't if it thinks the engine hot enough to start.

J

[RonVan]

Thanks John!

The relay in the photo started clicking when I plugged my code reader in. I will check that out and replace if necessary. The PCM is located in the lower left of your photo by the brake booster, correct?
How often do those fail? I assume they are fairly pricey?

[john8662]

PCM is in the cab, behind the glove box in the dash. The box pictured is the ABS Brake controller. PCM's do fail, but not very common, especially in one of these rigs.

The relay shouldn't click continually, it should click only once (one click) the key is turned to run (to signal turning on the glow plugs, by enabling the glow controller).

A problem in this area is most likely either the relay, or the coolant sensor on the water/thermostat crossover pipe (sensor plugged into passenger's side of engine water crossover).

J

[RonVan]

Thank you very much John!
I will try to get the beast running today by performing your suggestions.

[RonVan]

OK ------- That did not work. Where is the Inhibit switch located? Not along the orange (Pin C) wire as page 37 of the Deisel Page 6.2 trouble shooting guide depicts. Is this switch possibly internal to the controller?? I have chased the orange wire through the fire wall and have found no switch. It factory splices to the gray glow plug wire as show, but no switch?????

[john8662]

PCM = Powertrain Control Module, in short the computer, yes your 1990 has one.

ECT = Engine Coolant Temperature, it's a sensor mounted in the water crossover (thermostat housing) that reports to the computer what the temperature is. This sensor is separate from the one that runs the gauge inside the cab.


Here is the other relay that works in conjunction with the computer, and the glow plug controller. This relay simply "turns on" one of the pins on the controller and allows the controller to function. The glow controller itself is still self-regulated, and will come on if the temperature falls below a certain threshold, and won't if it thinks the engine hot enough to start.

The information was already in front of you, all you had to do was read...

There isn't an inhibit swich on a 1990 6.2, this whole relay, sensor, computer thing replaces that!!!

[RonVan]

Not sure if I see where it says "there is not an inhibit switch" in the 1990 6.2. The wiring diagram is misleading. I will just replace the glow control module.

Thanks for your help, John...........