I really need help...
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New User
Joined: Mar 2014
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I really need help...
I have a 2002 7.3 F250 that I have been having starting issues when it is below 35 degrees. It will start fine as long as it has been plugged in, but I cant do this at work, or if it has a little bit of warmth left in it. I don't make much money and really cant afford to put more into it, so far I have replaced both batteries, all battery wires, starter, alternator, glow plugs and gaskets, glow plug relay. if I lay a screwdriver across the two posts on the relay for about 20 seconds it will start. I am not mechanically inclined and pretty deep into the expense of this so far, can anyone help?
Post Fiend
Joined: Mar 2007
Posts: 26,966
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From: Texas
Do you have a multi meter or a test light? You need to test the glow plug relay to make sure it's still working. There's a big post that has a wiring coming from the battery so that should always read hot or trip the light. The other post should show voltage right after the key is turned on.
Too bad you've wasted so much time and money if you really don't have any to spare. If laying a screwdriver across the two large posts gets it to start every time, then you could always just keep doing that.
Or you could just use the spare that Ford gave you for free. Right next to the GPR is another relay that you actually don't need. It's a little taller and clocked different, but just swap the two relays and use the taller one for your new GPR.
Too bad you've wasted so much time and money if you really don't have any to spare. If laying a screwdriver across the two large posts gets it to start every time, then you could always just keep doing that.
Or you could just use the spare that Ford gave you for free. Right next to the GPR is another relay that you actually don't need. It's a little taller and clocked different, but just swap the two relays and use the taller one for your new GPR.
Cargo Master
Joined: Oct 2010
Posts: 2,089
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I had a problem with mine that i still have not resolved and it could apply to you as well.
If you do what f350 said and for some reason the relay does not work and you have voltage on the big terminal and the small terminal, check the other small terminal for ground. The small trigger wire on the GPR is keyed voltage. The pcm then grounds the GPR to make it work when the conditions are right.
My truck will not send the ground at anytime ever. It should have based on the sensor readings but would not. Over 2 Years ago, I ran a momentary switch to ground it when cold and have not had another starting issue when cold. I assume I have a bad wire or connection between the gpr and pcm or maybe even a pcm issue but have not taken the time to chase it down.
If you do what f350 said and for some reason the relay does not work and you have voltage on the big terminal and the small terminal, check the other small terminal for ground. The small trigger wire on the GPR is keyed voltage. The pcm then grounds the GPR to make it work when the conditions are right.
My truck will not send the ground at anytime ever. It should have based on the sensor readings but would not. Over 2 Years ago, I ran a momentary switch to ground it when cold and have not had another starting issue when cold. I assume I have a bad wire or connection between the gpr and pcm or maybe even a pcm issue but have not taken the time to chase it down.
Post Fiend
Joined: Sep 2006
Posts: 7,426
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From: Sioux Falls, SD
You can handle this easily with a cheap multi meter and some good pics.
Here is a link to a good explanation & video on how to test what Chris already mentioned:
https://sites.google.com/site/woodnt...ow-plug-system
and a pic of what's under the hood:
Here is a link to a good explanation & video on how to test what Chris already mentioned:
https://sites.google.com/site/woodnt...ow-plug-system
and a pic of what's under the hood:
Cross-Country
Joined: Jul 2014
Posts: 51
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From: Bayfield, WI
Sounds like your signal wire for the GPR is what's faulty to me. If you have a piece of wire long enough to go from the signal stud to ground you can figure it out. I recommend a second person to turn the ignition on so you can stay under the hood. When the key is first turned on (cold engine) you should hear the GPR click. If it doesn't, but does when you ground the signal wire, there's the culprit.
Good luck!
Good luck!
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Ok guys, thanks for the help. Like I said, I don't really know what I'm doing here, but here is what I done. I got a multimeter and tested the pos. post, I had 12.63 and 0 on the other post then turned the key on and had 12.63 on the pos. post and 12.61 on the other post. You can definitely hear the relay click or snap when I turn the key But the truck still wont start if its cold unless I lay a screwdriver across the two post and jump it. So whats the next thing I should try?
Lead Driver
Joined: Jun 2004
Posts: 6,303
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From: Amarillo, TEXAS!
What is the voltage reading at the battery terminals with the key off? That 12.6 volt reading at the switched terminal of the relay sounds too high for the glow plugs to actually be energized. There's something odd going on, but I can't quite put my finger on it.
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Senior User
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Yeah, I agree with Kevin. Something isn't right. The voltage should drop to something like 11.5V when the glow plug circuit pulls from the batteries. If I had to reach and wonder why you see 12.6 on the outboard side of the relay, I'd say the relay is toast, and somehow the 12V signal voltage line (small wire on the side of the relay that always shows 12V) is getting passed through the relay somehow. That's the only explanation for 12.6v showing up there (versus 11.5 or so due to the heavy load from the glow plugs), and it coincides with the glow plugs working when the terminals are jumped with a screwdriver.
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Ok, I tested again and this time I got
1. Battery- 12.51
2. Pos. post- 12.51
3. Opposite post- 0
4. Opposite post with key on- 11.52
Like I said, I'm not mechanically inclined so I might not even be testing this right. But thanks with any help you can provide, I cant afford to take it back to a mechanic.
1. Battery- 12.51
2. Pos. post- 12.51
3. Opposite post- 0
4. Opposite post with key on- 11.52
Like I said, I'm not mechanically inclined so I might not even be testing this right. But thanks with any help you can provide, I cant afford to take it back to a mechanic.
Senior User
Joined: Mar 2008
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Well, that time it seems like the relay worked, as you're seeing a voltage drop that coincides with the heavy load presented by the glow plugs. The problem is, as the relays start to go bad, sometimes it's intermittent. I'm leaning towards a relay on it's way to the grave. Keep that screwdriver handy. You can also use jumper cables if you don't want to heat-treat your screwdriver.
Lead Driver
Joined: Jun 2004
Posts: 6,303
Likes: 576
From: Amarillo, TEXAS!
Those readings look like the relay is working. Try something, just to humor me. When the truck is cold soaked, let the wait to start light go off then wait another 20 seconds before attempting to start, and see if it starts more easily.
Senior User
Joined: Mar 2008
Posts: 337
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It's possible. Like Chris said, you can always swap it with the AIH relay, which is identical, and sits just in front of the glow plug relay. Or, like MK2Pierce suggested, it may have something to do with the signal wires from the PCM. The signal wire from the PCM switches from +12V to ground when the PCM dictates the glow plugs are needed. I believe ambient temp at the PCM and oil temp are the two inputs. Make sure your connection at the EOT sensor is clean (EOT sensor is shown in the pic posted above).