6.2L GP Issues

[flhtc01]

Hi, I am a new member here. I own 4 other diesels but, this is my first in a Pick-up. I need to know how to troubleshoot my GP system. Right now, it will not start as it is cold out. I am not getting the "wait" light and I am not hearing the click of the relay. Where to start? I just bought this truck and I have never seen the "wait" light but, I am told that it used to work.

My other issue is what is a good shop manual to buy for an 86 K30. I believe that the Haynes manual claims it does not cover the 6.2L. Any suggestions?

 

[3500GMC]

A test light will verify if the glow plugs are seeing voltage or not. Maybe the dash light is blown. If you get voltage to each GP wire, chances are all the GP's are burnt. If this checks out, test the leads in and out of the relay. You can jumper the coil side of the relay with +12V to see if the relay actually works. This should reveal a wiring issue.

Further, cold start issues can be fuel, advance, battery, starter related too. Slow crank speed is a bad thing.

There's a start. (pardon the pun)

 

[WarWagon]

I would upgrade to the 1993 glow plug controller as it has everything integrated. I would also use duraterm self limiting glow plugs. There are how to guides out there to convert.

The years use different systems, but, some stuff stays the same. It should help get you going without a book. 1988's (and 1986's ) have a temp switch on the passenger side back of the head. It kicks out the glow plugs when the engine gets hot otherwise the engine would blow them in half... So if it has failed open - no glow plugs. It is the same hole the temp sensor (or HOT light switch) goes in on the front driver's side literally side of the head. You also have a cold start advance switch in the thermostat crossover. Depending on the year you also have another (or different location) switch in the back of the head on the inside side where the coolant t-stat crossover would bolt up to. (Could be an overdrive switch as I am not sure.)

Your round glow plug controller may be screwed into the head driver's side rear. 1988's and 1993's have a squarish controller bolted in the same location. The round controller I think uses a separate relay. You can test it for 12v and function.

Without a book and in my experience, I suggest the switches fail. So I would test the switches first. Look for the one on the passenger side rear head. Both the inside and outside of the head. The switches should be closed. The outside 2 blade switch should be 0 ohm across the terminals cold, but, not shorted to ground. The cold start advance switch in the crossover should be the same. The one in the coolant crossover in the rear I think is shorted to ground when cold. Test when hot and see if they change to verify.

Next, test a couple glow plugs by pulling the wire and seeing 0-1 ohm to ground. The light is tied into the glow plug harness so when the plugs are on so is the light.

After the simple things you do need to hunt up a troubleshooting guide and wiring diagram. They are out there and may be in the how to section under a military manual on here.

Grounds and checking the glow plug harness for shorts and burned fusiable links can be done without a book.

 

[flhtc01]

I would upgrade to the 1993 glow plug controller as it has everything integrated. I would also use duraterm self limiting glow plugs. There are how to guides out there to convert.

The years use different systems, but, some stuff stays the same. It should help get you going without a book. 1988's (and 1986's ) have a temp switch on the passenger side back of the head. It kicks out the glow plugs when the engine gets hot otherwise the engine would blow them in half... So if it has failed open - no glow plugs. It is the same hole the temp sensor (or HOT light switch) goes in on the front driver's side literally side of the head. You also have a cold start advance switch in the thermostat crossover. Depending on the year you also have another (or different location) switch in the back of the head on the inside side where the coolant t-stat crossover would bolt up to. (Could be an overdrive switch as I am not sure.)

Your round glow plug controller may be screwed into the head driver's side rear. 1988's and 1993's have a squarish controller bolted in the same location. The round controller I think uses a separate relay. You can test it for 12v and function.

Without a book and in my experience, I suggest the switches fail. So I would test the switches first. Look for the one on the passenger side rear head. Both the inside and outside of the head. The switches should be closed. The outside 2 blade switch should be 0 ohm across the terminals cold, but, not shorted to ground. The cold start advance switch in the crossover should be the same. The one in the coolant crossover in the rear I think is shorted to ground when cold. Test when hot and see if they change to verify.

Next, test a couple glow plugs by pulling the wire and seeing 0-1 ohm to ground. The light is tied into the glow plug harness so when the plugs are on so is the light.

After the simple things you do need to hunt up a troubleshooting guide and wiring diagram. They are out there and may be in the how to section under a military manual on here.

Grounds and checking the glow plug harness for shorts and burned fusiable links can be done without a book.

Ok, I just crawled around the engine bay. I found the RH outside rear head switch. It was closed and not shorted to ground. .1 ohm. I found the LH front hot switch and it was not shorted. Single wire. What I could not find is the RH inside switch. There is a switch on upper inside of the LH head. and that measured the same as the RH outside switch. I have 12V at the GP relay. I confirmed that the bulb in the dash was good. Can I jump across the relay and will that cause the "wait" light to come on and cause the GP to heat up?

 

[WarWagon]

I see you have a CCUV... The Glow plugs had to be converted to 12v as they would have a resister on the firewall to drop the 24v to 12v. (CCUV's used a 12v glow system and needed the resister for 24v operation.) Need a picture of the GP controller and relay if you can. Does the relay have a 4 wire plug coming off it and is it a squarish unit? (Rather than the older round unit?)

Don't! If you jump the relay it will work once. Then all the glow plugs may burn out if they are not self limiting. Worse they swell up and are hard to get out. Newer plugs like the Duraterms are self limiting - these you can jump till the batteries die without the engine running and it won't hurt them. You need to read the PN off the glow plug to see what you have. Some you can do without removal. Don't assume they are all the same as the hard to reach plugs somehow get skipped or only bad ones replaced.

The glow plug controller for the 1988's have key on power, crank, glow plug voltage sense, ground, and the 'warmed up' switch on the head. 1993's omit the switch on the head.