GPR Voltage Low
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New User
Joined: Dec 2008
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From: Northern Minnesota
GPR Voltage Low
200 F350 w/7.3 - hard start cold. 12 volts in to GPR only getting 5 to 5.5 volts out to glow plugs ( brown & yellow wires) If i unplug the harnesses at the valve covers the output post voltage jumps up to over 12v. glow plugs are new and harnesses under the covers are new - 3rd GPR Napa 110. Any ideas as to why or where I'm losing the voltage?
It does start fine with the block heater plugged, getting into super cold weather now and it will be ( it is ) a problem.
It does start fine with the block heater plugged, getting into super cold weather now and it will be ( it is ) a problem.
Post Fiend
Joined: Feb 2007
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From: Dallas-Ft. Worth
If you're measuring 12V on one side of the GPR and only 5V on the other, that's where the drop is happening. When the GPs are on, measure between the input & output posts on the GPR. Any more than a volt or so is too much drop across the relay.
Postmaster
Joined: Dec 2008
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I would disconnect the yellow and brown outputs to the glowplugs then re-measure. Get a base line and then connect one at a time and see if it changes in voltage. You could have a wiring issues that is causing a voltage drop.
Lead Driver
Joined: Jan 2007
Posts: 6,708
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From: Kiowa CO
Here's a good step-by-step of testing the GPR.
Welcome to guzzle's Stancor GPR replacement Mod Web Page
I have a feeling that more of these posts will come up as the weather changes.
Welcome to guzzle's Stancor GPR replacement Mod Web Page
I have a feeling that more of these posts will come up as the weather changes.
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From: Northern Minnesota
Thanks for the replys - Here's a little more info. As I said we unplugged the harnesses at the valve covers and the voltage on the output ( large lug ) went up to 12+ almost the same as the input side. GPR cycles - does everything it should. Glow plugs test fine checking the pins, they are new and the wire harness's under the covers are new. EOT is new and the Baro Air Sensor is good.Reconnected the harness's and voltage was down to about 6 at the output lug on the gpr. It is a puzzler. 
I did notice last night that the PCM box is missing its screws that hold it to the frame under the dash - does anyone know if this is a grounding point for that controller and could it effect the voltage or the relay? I'll reattach it regardless just so it isn't bouncing around. I will try the screwdriver across the lugs - its about 25 out windy, cold and snowing, doesn't take long to cool down to I don't want to start mode....
I did notice last night that the PCM box is missing its screws that hold it to the frame under the dash - does anyone know if this is a grounding point for that controller and could it effect the voltage or the relay? I'll reattach it regardless just so it isn't bouncing around. I will try the screwdriver across the lugs - its about 25 out windy, cold and snowing, doesn't take long to cool down to I don't want to start mode....
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Post Fiend
Joined: Feb 2007
Posts: 14,541
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From: Dallas-Ft. Worth
What you're seeing is normal. When the relay has no current flowing with the GPs disconnected, you'll see the source voltage. Put a large load across it, and the voltage drops. That's why I suggest you measure between the two terminals with the GPs connected and operating normally. If you see about 6V there, the relay is bad again.
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New User
Joined: Dec 2008
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From: Northern Minnesota
I've ordered the Stancor relay. Voltage through was less than 6v. It took about 45+seconds jumping the terminals with a screwdriver, then fired right up. nice and smooth as well, cold idle etc all working as should. I'll replace the NAPA 110 with the Stancor and hopefully - problem solved. 
Post Fiend
Joined: Feb 2007
Posts: 14,541
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From: Dallas-Ft. Worth
When you get the new one in, measure the voltage drop between the input & output terminals with the GPs activated. It should be very low. Here, the lower the number the better. If you're seeing 5-6V between the terminals, I'd bet the relay is getting pretty hot... 
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From: Northern Minnesota
Installed the Stancor and truck fired up ( was plugged in ) left it for about two hours unplugged ( about 25 degrees out ) and it fired up. Big test will come at 4am. I did notice a heavy draw when I hit the starter, will test the batteries and starter draw, may have worn it out with all the cranking since last spring, I am seeing a load when the glow plugs are on - which I wasn't seeing before. I will also check the voltage across the GPR when I have time tomorrow. I'm also thinking of adding a ground strap to the engine from the chassis - I think there still might be a ground issue somewhere along the line that's contributing to some of the problems........I think I like that Stancor already 
Logistics Pro
Joined: Aug 2009
Posts: 3,609
Likes: 324
From: Arizona
Here's a good step-by-step of testing the GPR.
Welcome to guzzle's Stancor GPR replacement Mod Web Page
I have a feeling that more of these posts will come up as the weather changes.
Welcome to guzzle's Stancor GPR replacement Mod Web Page
I have a feeling that more of these posts will come up as the weather changes.
Is this a typo on Guzzle's page?
" If your voltage measurement there is less than .2 volt lower than the "always hot" post, the relay is beginning to have the contacts burned from arcing"
Shouldn't it read "more than .2"?
Post Fiend
Joined: Feb 2007
Posts: 14,541
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From: Dallas-Ft. Worth
Yep -- your are correct... DOH!!
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New User
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From: Northern Minnesota
