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Discussion Starter #1
OK, I have read all about the glow plug relays, and how to ohm out the glow plugs. And I cant find an answer to my question. Maybe its in there and Im not smart enough to decipher it.

I have replaced my relay 3 times now and I still have no power at the post going to the glow plugs. I 1st used the GPR109 and the last 2 have been GPR110 both from NAPA. Starting to think it isnt the GPR.

When the key is turned I get power on the 2 small posts but not the big one going to glow plugs.

Is there a possibility that the EOT is bad? and is there a way to test it?

What the heck could it be? Its getting colder and I dont want to have to plug the ol'girl in every night.

2002 CC F-350 4x4
 

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Discussion Starter #2
When I use a screwdriver to go between the 2 large posts she fires right up. Now that tells me bad relay, but dang it! this is the 3rd new one! It cant be bad again NAPA will black list me.

Someone has to have an answer.
 

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I havent had any luck with napa or carquest relays. Go with alliant power, we havent had any issues with them.
 

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The Oracle
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pull the control wire off the relay, hook up an ohm meter and see if it grounds when the key is turned on. if it does, you've had 4 bad relays(unlikely even with aftermarket garbage) if it does not, you have either a bad wire from the PCM to the GPR and need to start chasing it, or you have a bad driver in the PCM (replace PCM or wire a manual switch to control it)
 

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Discussion Starter #6
pull the control wire off the relay, hook up an ohm meter and see if it grounds when the key is turned on. if it does, you've had 4 bad relays(unlikely even with aftermarket garbage) if it does not, you have either a bad wire from the PCM to the GPR and need to start chasing it, or you have a bad driver in the PCM (replace PCM or wire a manual switch to control it)
OK just so my tiny brain can comprehend this, when I pull the wire off the EOT should I see resistance on it until the key is turned? And if it goes to OL on the meter when the key is turned then it is good?

Also there is a fuseable link wire on the large post that, do you know where that goes? and could that be the suspect?

Thank you very much for your help!
 

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The Oracle
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What I said has nothing to do with the EOT. One of the small wires on the GPR is hot with key on, the other comes from the PCM. The PCM supplies ground to activate the relay.

As for the fusible link, its not your issue since you clearly have power at the big post because your said your bridged it with a screw driver and it worked
 

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Discussion Starter #8
Sorry, I had EOT on my mind. Now I see you said control wire off of relay.
 

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Discussion Starter #9
Alright BigRed, you've been ridiculously helpful so far. Now if I pull off the control wire from the GPR how can I tell if it grounds out when I have someone turn the key?

Sorry if its a dumb question but im just trying to get it right.

Thanks again for all of your help.
 

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The Oracle
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hook up your (ohm) meter to the wire and to battery ground, have some one turn the key to Run (not crank) the meter should show continuity.

a second(maybe slightly simpler to understand) way would be hook your (volt) meter between the wire and battery positive.have some one turn the key to Run (not crank) the meter should show battery voltage

if you do not get the desired reading, then you either have a bad wire or a bad pcm (wire is more likely)
 

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Discussion Starter #11
I will check that out when I get an extra set of hands to turn the key.

Thank you very much for your help!

If I cant find the problem, I think that I will direct wire the glow plugs to a switch in the cab. :)

Thanks again
 

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If you unplug the EOT sensor with the key on the GPR should be commanded on and supply voltage to the glow plugs. Quick and easy way to check relay, computer, and control wiring all at once.
 

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Discussion Starter #13
If you unplug the EOT sensor with the key on the GPR should be commanded on and supply voltage to the glow plugs. Quick and easy way to check relay, computer, and control wiring all at once.
So your saying with the key on , not started, if I unplug the EOT and it warms the glow plugs and the truck starts then my EOT is bad and everything else seemingly works?
 

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Doesn't rule out a bad connection at the EOT sensor or the sensor itself, but everything else.
 

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Discussion Starter #15
Heading out this morning to install my 4th GPR. I bought this one from International and not NAPA and surprisingly it was half the price of NAPAs relay from China.
 

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Discussion Starter #16
Mother*&%$#@ IT DIDNT WORK!!

What the hell?
 

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Discussion Starter #17
With the help of BigRed I finally have solved my relay issue. A $5 push button and 20 mins time I have a relay that warms my glow plugs.
 
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