GPR Won't Jump
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Tuned
Joined: Jan 2012
Posts: 270
Likes: 0
GPR Won't Jump
ive been dealing with hard starts and did the screwdriver test. I jumped the two posts on the GPR (the one closest to the cab, I'm assuming) and there wasnt a spark or click or anything. Could the fuse be blown? If so what else is on this circuit? It blows a huge cloud of white smoke after about 3 or 4 times of trying to start. The ammeter doesn't go down either at the beginning.
Laughing Gas
Joined: Apr 2004
Posts: 776
Likes: 42
From: STL MO
U really need a cheap multimeter from sears or any other hardware store. There are two large copper posts. The one at the from is connected to the battery plus and should measure 12v at least. If it measures right and u still do not see spark when u jump the two, that means u have a open circuit between the other post and your GPs. If no 12v power measured, you have an open from there to the battery. Without any means to measure, it's near impossible to figure out why. Erwin
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 10
From: Snohomish, WA
Take a look at this video I put together to check GPR relay operation. If you have a simple 12v test light, you can verify the operation easily. You should also look into the GPR LED MOD. You add a small LED to the circuit in the cab. It will always tell you exactly when the GPR is energized.
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Tuned
Joined: Jan 2012
Posts: 270
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Thank for all the help and the video. I'm guessing the led mod is just two wires with ring terminals connected to the posts that make the light turn on when it is connected. I've got 2 multimeters and I believe my dad has a test light somewhere. It's up on stands right now to replace the right hub and ball joints.
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 10
From: Snohomish, WA
The GPR LED MOD is only one wire. You run the positive wire to the post on the GPR that the glow plugs are hooked too (Inside most large terminal). Then you run the negative to a ground in the cab. When the GPR is energized, the 12V signal will be sent to the LED in the cab and you will always have an instant notification that the GPR Relay is working. You will also learn when the GPR is not required by the PCM and you will find that helpful too.
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Senior User
Joined: Jun 2012
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I did the GPR LED mod and found out mine is bad. Time to get a stancor 
. And it explained a lot about the hard starts this winter.
. And it explained a lot about the hard starts this winter.
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Thread Starter
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Tuned
Joined: Jan 2012
Posts: 270
Likes: 0
Take a look at this video I put together to check GPR relay operation. If you have a simple 12v test light, you can verify the operation easily. You should also look into the GPR LED MOD. You add a small LED to the circuit in the cab. It will always tell you exactly when the GPR is energized.
GPR operation - YouTube
GPR operation - YouTube
Cargo Master
Joined: Mar 2006
Posts: 2,502
Likes: 2
From: Bend Oregon
Used your video and put the post to ground for about 10 seconds, went to start it and it was like it has been running all day. Within half a second it was on and absolutely no white smoke. Smooth as well. Once the ball joints and hubs are in and she's back on the ground I'm going to change it.
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Tuned
Joined: Jan 2012
Posts: 270
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It would have to be between the PCM and the relay, correct? If the GPR is working and applying power to the glow plugs then what is a common problem in the first part of the system?
Cargo Master
Joined: Mar 2006
Posts: 2,502
Likes: 2
From: Bend Oregon
I'm just guessing here......
you have either:
1: A broken wire between the PCM connector and the relay harness
or
2: the PCM is not commanding the GPR to come on.
2a: if the PCM is not commanding the GPR to energize is it a defective PCM or a defective temp sensor not sending the correct enviromental parameters to the PCM?
I am not sure what the PCM looks at to command the GPR to energize but I believe oil temp may be one of if not the only parameter involved, possibly ambiant ait temp as well. Maybe someone with a little more knowledge on this will chime in.
you have either:
1: A broken wire between the PCM connector and the relay harness
or
2: the PCM is not commanding the GPR to come on.
2a: if the PCM is not commanding the GPR to energize is it a defective PCM or a defective temp sensor not sending the correct enviromental parameters to the PCM?
I am not sure what the PCM looks at to command the GPR to energize but I believe oil temp may be one of if not the only parameter involved, possibly ambiant ait temp as well. Maybe someone with a little more knowledge on this will chime in.
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 10
From: Snohomish, WA
The glow plug system is electronically controlled by the Powertrain Control Module (PCM). If the oil temperature is below 131°F the PCM will energize the glow plugs immediately after the key is placed in the ON position. Then, depending on the readings from the engine oil temperature (EOT) sensor and the barometric pressure (BARO) sensor, the PCM determines how long the glow plugs will be on.
That is from my Glow Plug Page.
That is from my Glow Plug Page.
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