Cold start issues
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Mountain Pass
Joined: Dec 2003
Posts: 100
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From: linden, mi
ok glad i didnt drive to airport got a ride came home 30f out would not start. this truck has never done this. How do you test the glow plug relay. I do hear all the clicking when I turn the key. It fires wants to start but does not? the only other codes was a egr forgot the which one? All 8 glow plug were replaced did not help it?
Posting Guru
Joined: Mar 2014
Posts: 1,468
Likes: 5
From: Salt Lake City, utah
Does it start if you plug it in? The best thing you could do is get ForScan and run a glowplug system test that will give you an idea of what's going on. If you get codes for x-amount of glowplugs then you may need a GPCM.
Posting Guru
Joined: Mar 2014
Posts: 1,468
Likes: 5
From: Salt Lake City, utah
Maybe someone has the pinout procedure so you can ohm things out just to check the wiring and for power before you spend the money on a module. But if the glowplugs are new and the wiring fully seated it's most likely the module. It's 180.00 gamble without checking those things out first.
Fleet Owner
Joined: Nov 2003
Posts: 27,881
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P0678 - #8 glow plug circuit - HOWEVER frequently the code for the #8 glow plug circuit really means the GPCM as others have indicated.
You can disconnect the glow plug harness and test the resistance. The harness should read 0 to 1 ohm resistance.
The red wire on the black GPCM connector is the circuit for the #8 glow plug. Each plug should read 0.1 to 2 ohms resistance. If that is ok (and it should be since it is new), then you PROBABLY need a module (again as the others are telling you).
A frequent GPCM problem indicator is low idle rpms if/after it starts (say around 450 rpm).
You can disconnect the glow plug harness and test the resistance. The harness should read 0 to 1 ohm resistance.
The red wire on the black GPCM connector is the circuit for the #8 glow plug. Each plug should read 0.1 to 2 ohms resistance. If that is ok (and it should be since it is new), then you PROBABLY need a module (again as the others are telling you).
A frequent GPCM problem indicator is low idle rpms if/after it starts (say around 450 rpm).
Hotshot
Joined: Dec 2014
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From: Jersey Shore
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Mountain Pass
Joined: Dec 2003
Posts: 100
Likes: 0
From: linden, mi
Replaced glow pug relay seems to start better but have tried it below 28F however I noticed oil on my blue boot to the intercooler, there should not be oil in intercooler? I did break a turbo shaft and ingested alot of oil but that was 25K miles ago.
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