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Discussion Starter #1
Hey guys, I recently bought a 1997 Ford F-250, 7.3 stock, 5 speed 4x4, with a 185k. I was having some trouble with the glow plug system. I replace the GPR with a new motorcraft one. When the truck is running I have power at the little treminal thats suppost to have ground from the PCM. Does it always supply ground or does it supply ground to turn the GPR on and then It show positive when the truck is running, or is my PCM on its way out. When the key is off I just have power at the feed to the relay then when the key is on I have power at all 4 post on the GPR. Then when its done its cycle it has power at the 2 small terminals and the 1 big feed terminal when the truck is running. Also checked the UVCH and it looked good, and I replace 4 glow plugs on the passenger side while I was in there. The old ones were still good but becasue I had the new ones why not, and i had power to all the glow plugs on that side. Didn't check the driver side yet it got to dark last night. Thanks for the help.

Shane
 

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Member
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124 Posts
Are you sure you got a Glow Plug relay and Not a starter relay ? they are different...
 

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Super Moderator
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4,247 Posts
I was having some trouble with the glow plug system. I replace the GPR with a new motorcraft one. When the truck is running I have power at the little treminal thats suppost to have ground from the PCM. Does it always supply ground or does it supply ground to turn the GPR on and then It show positive when the truck is running, or is my PCM on its way out.
WOW! You actually did the test correctly and your idea is 100% correct! The PCM only grounds the one small terminal WHILE it wants the GP to be on, so everything is working correctly thus far!

When the key is off I just have power at the feed to the relay then when the key is on I have power at all 4 post on the GPR.
Yea, that's a problem... the PCM is not grounding the one small terminal as it should be, at least with the engine "cold".

Then when its done its cycle it has power at the 2 small terminals and the 1 big feed terminal when the truck is running. Also checked the UVCH and it looked good, and I replace 4 glow plugs on the passenger side while I was in there. Thanks for the help.

Shane
It sounds like either the PCM thinks the engine is warm enough not to need the GPs to be turned on, or there is a wiring problem between the PCM and one smaller terminal of the GPR.
 
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