I just changed the GPR when I thought that was broken but it didn't fix the problem.

When I turn the key it wont engage the glow plugs. (you can see when it does as the volt gauge drops to almost nothing...)

There are two small cables aswell from the GPR... What are those?



Any ideas?

 

What GPR did you purchase?

One small wire goes to fuse #22 so has power with key on.
Other small wire is pulled to ground by the PCM to activate the relay.

 

An expensive one. Thanks, gonna check those out.

 

"Expensive" doesn't mean "good". What BRAND did you get?

Have you TESTED the circuit? Resistance of the glow plugs, continuity of the wiring, etc?

 

I know and I saw now that I kind of lied there... It wasn't that expensive.
Called "Diesel Rx" but it should just work at least right?

 

Replace with a plow solenoid...and wire a push button on dash...done! Plus they have a loud click...so when they crap out you know it!

 

Do your diagnostics then get back to us. No need to butcher anything to make thing work like they were designed to

 

THe EOT sensor is first in line .. Make sure that is working

 

What is that?

edit: ah Engine Oil Temperature...

I'll check it. If I understand it right that would tell the GPR that the engine is cold all the time if that was broke is that right? In that case the glow plugs should be on rather than off all the time...

 

It's not that simple. Everything goes through the PCM. The PCM reads the EOT, and sets the run time for the GPR accordingly. The MAX GPR run time is two minutes. But on _some_ trucks, if the EOT reports the engine is fully warmed up, the PCM doesn't energize the GPR at all.

But as said, start with the simple electrical tests on the relay and its circuitry.