PCM not activating the GPR

[Jamesingram]

I just bought a 2000 F-250 and the glow plugs were not working and so I did some research and found some tests to check the GPR first, it was bad, replaced it and the Truck still wouldn't warm the GP's. I jumpered the relay and the relay worked fine, truck started. One problem I may have caused is when I was testing the old relay last night and half asleep I didn't think to dis-connect the PCM wire from the relay when I applied the 12volts directly to it. Could that have ruined the PCM and thats why it won't turn on the GP's? No check engine light and truck seems to run fine. Are there any other fuses in line or does anyone have a wiring diagram for that circuit?
On a side note is there a disadvantage or problem to useing a independant switch to activate the realy and just leave the PCM disconnected from it?

[no-tel-in]

ring out the 2 control wires back to the big plug on the pcm, I had a similar problem recently and there was a bad connection in the big harness plug over drivers vc, I cleaned the connector, and had continunity back to the pcm, put it all back together and it worked. so good luck!

[dray8165]

You may have fried your PCM. The PCM doesn't send 12V+ to the GPR, it completes the ground.

The GPR has a constant 12V + at one of the large terminals and one of the small terminals. When the PCM activates the GPR, it completes the ground, which triggers the solenoid, and 12V+ is supplied to the glow plugs. If you ran 12V+ to the negative lead of the PCM, its anybody's bet as to what happened.

Read this:

Hard/No Start? Check here first. - Diesel Forum - TheDieselStop.com

[timfire911]

I have been doing a lot of reading on this site latley. I have put an OHM meter on the 2 big posts of the back relay and got nothing that would hold a certian number. It jumped from 0 to 16. something then back to 0 and the to 11. something and back to 0 and so on. I put a jumper wire on those 2 treminals and it got red hot with the ingition on but it started right up with no problems. If I don't plug it in below 40 to 50 degrees it is hard to start, the colder it is the harder it is to start. I have already changed out the gp's with brand new motorcraft. Please understand I am new to the diesel lifestyle. I have a 2002 F-250 w/ 7.3 approx. 170,000 miles, 6 inch suspension lift, 35X12.50 R16.5. I have done nothing else, performance wise, to the motor even though I would like to. Now, once it starts it runs great and in warm weather it runs great. Please help me fix my baby!!! Thanks

[dray8165]

Originally Posted by timfire911

I have been doing a lot of reading on this site latley. I have put an OHM meter on the 2 big posts of the back relay and got nothing that would hold a certian number. It jumped from 0 to 16. something then back to 0 and the to 11. something and back to 0 and so on. I put a jumper wire on those 2 treminals and it got red hot with the ingition on but it started right up with no problems. If I don't plug it in below 40 to 50 degrees it is hard to start, the colder it is the harder it is to start. I have already changed out the gp's with brand new motorcraft. Please understand I am new to the diesel lifestyle. I have a 2002 F-250 w/ 7.3 approx. 170,000 miles, 6 inch suspension lift, 35X12.50 R16.5. I have done nothing else, performance wise, to the motor even though I would like to. Now, once it starts it runs great and in warm weather it runs great. Please help me fix my baby!!! Thanks

You are running non-standard tests. Read the link listed above and walk through those tests. It is possible to have a GPR that has intermittant contact, but you say it is new. That might point toward a bad connection somewhere - but still - you have to run the tests that make sense to rule out your problem.

[Dean'o]

I have the exact same problem with my truck. I took it to the mechanic last week and he said I have a bad PCM. By the way, can a person get one from a junk yard and does it have to be from a similar model truck (same year, same options, etc)? Advance auto can get me one for a little better than $300 and then I guess it will have to be programmed too.

[no-tel-in]

I was about to buy a pcm... but definately read my earlier post. Ring out the small red and orange wires all the way back to the large pcm plug, if it doesnt have continuity clean up the connections there, and in the plug over the drivers side vc!