I own a '92 6.5 TD in a 4x4 3/4 ton regular cab chevy. A few days ago I turned the truck off, unloaded it for about 15 mintues and tried to start it, the glow plug light didn't turn on, so I figured maybe it was warm enough not to need it, eventhough its needed glow plugs right after I've shut it off before. So I tried starting it and it didn't go, turned key off, then back on to see if glow plug light would work, didn't, so tried starting anyway, gave it a little gas and it went. Got the truck home, turned it off, then back on again and the GP light worked. Few days go by not using the truck, then decide to drive it this morning. GP light worked fine and truck started. Get to work, turn it off, turn back on GP light works. 8 hour day of work goes by go to start truck GP light works, get home, turn it off, turn back on, GP light works. Go inside for about 15 mintues get back in the truck and GP light don't work and truck doesn't start even after giving it a little gas.

In conclusion it seems like the GP light will work right after the truck is turned off or after it has sat and cooled down, but doesn't work about 10-30 mintues after its turned off.

Other things that to note is that the temp gauge only comes up to about 100 degrees even after a new themostat, and I"m pretty sure its kicking out normal heat out of the heater so I'm assuming the temp sending unit is going bad. Also the amp gauge fluctuates when I use the turn signals, the needle bounces pretty good, but seems to keep the batteries charged fine.

I've tried unplugging the wire into the temp sending unit to see if that controls the GP's but it didn't start either.

Any help would be great. I was hoping to get more than 1000 miles out of it before I started wreching on it.

My guess is a bad battery connection, mine is doing the same things you describe, I have tracked it down to a crummy power connection on the passenger side. Clean all the connections and check all the grounds and that may be all you need to do.

I agree with checking the battery conections. Also check your GP relay my GP's acted up for about a week then just stopped working no glow plug light and no start. Found the connection on the relay had rattled loose loose (go figure being unnecissarily mounted on the engine) allowing it to get hot enough to melt the terminal off of the relay.

My glow plug light hasn't been working very often lately but the glow plugs are working. I just wait till I hear the click then it starts right up. (my battery connections are ok)

Where is the glow plug relay? Do you clean just the connections at the battery? Or every where there is a ground strap?

The engine turns over fast, so somthing must be getting a good connection, right?

GP relay is located behind the intake manifold next to the fuel filter on the drivers side. It has a 3 or 4 wire input on the top and (2) 10 guage wires connected on the side. When I wriggled the 10 guage wires on mine the terminal fell off in my hand. Let us know what you find.

I found that the large red wire going into the Glow Plug relay had worn through the insulation on the firewall and must have been rubbing on the metal so it wore through the coating over the wire and bare wires were showing. I put tape over the damage and re-routed the wire. The nut was a little loose too. I guess only time will tell if that was the problem or not, doesn't seem like it would have been since the problem only seems to happen when the vehicle is warmed up.

Is there some sort of sensor by the turbo that some trucks had problems with heating up and causing not to start? I belive the fix was to relocate the sensor?

We are having the same exact problem with our truck. We think it is the GP inhibit Temperature Switch, but when we follow the wiring diagram out of the Haynes Diesel Techbook we can't find the switch. Does anyone know where it is located.

Ther inhibit switch screws into the cylinder head typically at the passengers rear. To the best of my knowledge it was only used on MFI trucks and is similar switch/location as the cold advance switch. Haven't messed with one of these since my 84 which had the wires tied together at the inhibit switch. I think it screws into an accessory boly hole if memory serves.