Dreaded GPR problems - Ford Powerstroke Diesel Forum
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Old 11-28-2013, 07:58 AM
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Dreaded GPR problems

2002 7.3, had glow plug relay problems since I purchased it. I believe the orange wire is the culprit. Main large hot wire shows 12v, smaller red wire shows 12v when key on, the ORANGE wire shows 4.4v for the GP cycle time then 0. I've researched and from what I've gathered this should be a switched GROUND. Any ideas how I could be seeing 4.4v?
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Old 11-28-2013, 08:18 AM
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It's because it's In the circuit. That is, it's connected to the other side of the coil, that has 12v in it. I'm not sure about the Orange & Red thing. Take them both off (this is the sm wires) and you should see 12v in one and nothing in the other (key on). Then, when cold enough to activate the GPs, you should see a path to ground in the other (measure this with a meter that has one lead on it and the other on 12v + from somewhere). Depending on how cold it is you'll see that ground path (it will read 12v) for 15-90secs totally independent of the WTS light.

The Real test for the GPR is to measure the two Big terminals voltage, while the plugs are activated, to see if there's much of a loss between them.

Have you gone over this Sticky? -> Troubleshooting GPR & GP's

Last edited by NoRalPh; 11-28-2013 at 08:21 AM.
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Old 11-28-2013, 09:04 AM
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Ok, it's 30 here so the relay should be on for the full 120 secs or so. The 4.4 volts is measured at the small orange wire with both the small wires off, the small red always reads 12v with the key on. The 4.4v will go to 0 after the glow plug cycle is suppose to go off. The other large terminal never sees any current at any time. I'll try the path to ground tomorrow. I was trying the ohm for grounding the orange trigger wire, but only ever saw 4.4v. I'll run threw the sticky also. Thanks for all the help!!
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Old 11-28-2013, 09:34 AM
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The one thing I haven't tried is " With jumper wires, apply voltage from the battery across the two small terminals. If your voltmeter now reads voltage on the output terminal, your GPR is OK, and your problem is in the PCM circuit that tells the GPR to activate."
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Old 11-28-2013, 01:17 PM
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Quote:
Originally Posted by Ests View Post
The one thing I haven't tried is " With jumper wires, apply voltage from the battery across the two small terminals. If your voltmeter now reads voltage on the output terminal, your GPR is OK, and your problem is in the PCM circuit that tells the GPR to activate."
That doesn't make sense to me at all....

To eliminate the PCMs control of the GPR what you would do is to GROUND the other side of the coil (the one with the Orange on it in your case, either connected or not, just so you're grounding the coil that has the 12v from the red wire connected on one side and now YOU'RE playing PCM by supplying that path)

That's how it works, you have 12v in with the key but if the other side doesn't have ground it doesn't go anywhere. When the PCM wants to activate the GPs a tiny transistor inside switches that wire to ground, the coil flows power, creates a Magnetic Field that pulls the contact arm inside closed, and connects the two Big Terminals together to supply the GPs. That's what relays do best, use a tiny amount of power (that a switch or transistor can handle) to switch a Large amount of power (like the Starter Motor or Glow Plugs).

They're really Already "jumped together" inside the relay with the coils windings, you're not doing anything if you put 12v in both sides (whoever told you that doesn't understand how a relay works ). Again, to activate it needs power on one side of the coil (sm terminals), and ground on the other, doesn't matter to the relay which-is-which...
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Old 11-28-2013, 02:52 PM
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So when you have 12v power to both small wires you have no power to the second big terminal? The relay is shot then plain and simple.

A quick definitive test, take a knife or something metal and put it accross the big terminals for 30 seconds or so then jump down and start the truck. You'll know if it worked. Also whatever you used will discolour from the heat.
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Old 11-28-2013, 03:23 PM
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Originally Posted by schlutzer View Post
So when you have 12v power to both small wires you have no power to the second big terminal? The relay is shot then plain and simple.

A quick definitive test, take a knife or something metal and put it accross the big terminals for 30 seconds or so then jump down and start the truck. You'll know if it worked. Also whatever you used will discolour from the heat.
No, no & NO!

That's not how it works,,, Key ON, with either the GPs activated or Not, you'll see 12v on Both sm terminals. There's Always gonna be 12v on both of them because they are connected inside, to one another, by the coil windings. Anytime there's 12v on one it's on the other too, and you see that because YOU are supplying the path to Ground with your testing device (meter, light, probe, whatever, it has a ground connection - right?).

Test the GPR by allowing the 12v supply to flow to ground by grounding the side which is Not supplying 12v (you have to remove them from the relay to know which wire that is)

I don't know what kind of "knife" you would want to short a 150 draw with (might never be the same ) I would do this with a jumper cable! But, Again, to properly test the relay you confirm 12v supply, confirm activation by grounding, confirm the internal contacts are OK by measuring the voltage difference at each of the Lg Terminals when activated...
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Old 11-28-2013, 03:44 PM
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I bought the truck in the summer so got relay was unknown. Once it got cold it wouldn't start so I purchased a new relay off eBay that came with the glow plug kit. Figured that one didn't work so bought another with the 180 degree off mounting and still the same thing. If you jump the two main terminals with jumper cables it starts fine. I'll try grounding the orange terminal with the wire off and see if that fixes things. I believe that is the problem. It sees 4.4v for the 120 seconds then goes dead, the other small red is 12v the entire time.
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