24 Volt glow plugs again

[boxkauto]

We have been battling a 1986 M1028 GM 2500 4x4 1GCHD34J1GF364611 glow plug issue. The glow plugs would not come on and have not for a long time. The Government owner has been using ether for at least a couple years.

We found all glow plugs burnt out so installed 8 new 13G plugs. Still no glow plug light or operation.

The temp sensor was shorted so we installed a new sensor on the left rear of the cylinder head GM # AD21352. This was supposed to be an updated sensor with a new wire connector included. Still no glow plug light or operation.

A manual bypass of the solenoid showed it worked but no voltage goes through. We were unable to locate a new one so we disassembled the old one and cleaned the contacts. Solenoid now works but still no glow plug light or operation.

All that is left is the controller. GM part #12034592. We installed it and still no glow plug light or operation.

All wiring seems to be correct. We are getting our behinds kicked on this one.

I want to stick with the original 24V wiring system

Can someone please help with this?

 

[m4A1]

Is the resistor still connected? It might be bad. The resister is the thing in the center of the firewall. It is used to drop the voltage to 12 volts for the glow plugs.

 

[boxkauto]

The resistor is connected properly and working. Thanks for the help.

 

[therbert]

Don't the glow plugs get ground through the block? Is the ground good?

I had an issue that was a grounding problem once..

 

[CCATLETT1984]

check the engine ground.

the glow plug relay on the firewall may be bad.
go to napa and ask for a borg warner S 55 (Thats letter "S" 55) relay.

 

[boxkauto]

Is there a chance the wiring schematic is wrong?

I am looking at the orange wire that goes from the glow plug relay to the glow plug module. The schematic shows it having 24V to it all the time but they call it the monitor wire. If it goes to the opposite side of the glow plug relay it will monitor glow plug on time and then it only provides 12v to the module. The system seems to work properly with this wire moved?

Any thoughts?

 

[CCATLETT1984]

I'm not looking at the schematics right now, but the glow plugs never get 12v. when you first glow the plugs 24v gets through until the resistors heat up and drop the voltage down to ~17 volts. This is why you cant put civilian plugs into the truck, they will burn up.

If you take a piece of wire and connect the terminal the has the light blue wire on it to a ground, do you get voltage to the glow plugs?

 

[boxkauto]

As soon as the solenoid is engaged the voltage to the plugs drops to 12.5V. I think this is normal.

The relay will work if the blue wire is grounded.

With the orange wire on the glow plug side of the relay the system works properly.

 

[Somemedic]

This might be a shot in the dark.
The goofy bulb that lets u know the alts are working or not have to be good for the alts to charge the system. Does the "wait" or "W.I.F" bulb have to work for the GP system to heat/operate? I hope thats not too "newbie" of a question. I was told that the water in fuel light can come on for more than just water detected in the fuel system (obstructions or is it a vacuum detected in the fuel system) just FYI...

 

[CCATLETT1984]

the wait light does not affect the operation of the glow plugs at all.