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post #1 of 13 (permalink) Old 05-05-2019, 09:51 AM Thread Starter
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Glow plugs relay issue

So I recently replaced the GPR and all the glow plugs. For a while the engine started up immediately after the the light went out, it was great. Lately the start has been slowing down more and more, day by day. Until yesterday when I had to crank twice to get it going.

I checked one of the big poles without turning the key and it is getting a 12v reading.

I checked the other pole with key turned. With every click of the relay the voltage meter jumps. Never to 12, but to around 6 or something. Then it pulses with the clicks of the relay.

Is it common for it to pulses like that? If it is common, wouldn't be pulling to 12?

What do you think could be the issue here? Also, am I damaging my glow plugs at all by continuing to try to start like this?
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post #2 of 13 (permalink) Old 05-05-2019, 03:16 PM
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Originally Posted by koots55 View Post
So I recently replaced the GPR and all the glow plugs. For a while the engine started up immediately after the the light went out, it was great. Lately the start has been slowing down more and more, day by day. Until yesterday when I had to crank twice to get it going.

I checked one of the big poles without turning the key and it is getting a 12v reading.

I checked the other pole with key turned. With every click of the relay the voltage meter jumps. Never to 12, but to around 6 or something. Then it pulses with the clicks of the relay.

Is it common for it to pulses like that? If it is common, wouldn't be pulling to 12?

What do you think could be the issue here? Also, am I damaging my glow plugs at all by continuing to try to start like this?
Have you checked to make sure that all the glow plugs are still good, a bad one or two really messes with the system. Would start there.
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post #3 of 13 (permalink) Old 05-05-2019, 04:06 PM
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Randy is right, 1 or 2 bad ones will mess everything up. I’m not sure about your other questions. It’s pretty warm to even need glow plugs but I still use mine as well.

I had a start issue, changed batteries, glow plugs, relays....I did have bad glow plugs (5 of them) and that helped a whole lot but also ended up being my starter not spinning fast enough. I hear we can upgrade starters now from newer fords to really put down some turning power but that’s a different subject.
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post #4 of 13 (permalink) Old 05-05-2019, 04:22 PM
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What type of glow plugs did you use?

Most aftermarket ones will cause problems with early burn out and swelling in the head.

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post #5 of 13 (permalink) Old 05-10-2019, 09:19 AM Thread Starter
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Have you checked to make sure that all the glow plugs are still good, a bad one or two really messes with the system. Would start there.
I havn't checked the glow plugs yet. I changed them all only about 4 months ago. I can check them again tho. So, the GPR is fine bouncing only up to about 6 volts with every click?

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Originally Posted by Texas_proud77836 View Post
Randy is right, 1 or 2 bad ones will mess everything up. Iím not sure about your other questions. Itís pretty warm to even need glow plugs but I still use mine as well.

I had a start issue, changed batteries, glow plugs, relays....I did have bad glow plugs (5 of them) and that helped a whole lot but also ended up being my starter not spinning fast enough. I hear we can upgrade starters now from newer fords to really put down some turning power but thatís a different subject.
Hmmm.... I guess I can check the starter. All the plugs are new, can check them again. I guess I'm just confused about the relay only bouncing to 6V with every click after the plugs are warmed.

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What type of glow plugs did you use?

Most aftermarket ones will cause problems with early burn out and swelling in the head.
I used motorcraft
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post #6 of 13 (permalink) Old 05-10-2019, 09:43 AM Thread Starter
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one thing that just happened is it wouldn't start today. it's not super cold outside, but a little colder than it's been in a while
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post #7 of 13 (permalink) Old 05-11-2019, 11:20 AM
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No its not OK if its reading 6 volts.

Did you say you tested at the GPR when you got 6v?

I would fully charge your batteries and test them and then test your GPR properly.


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post #8 of 13 (permalink) Old 05-11-2019, 12:24 PM Thread Starter
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My batteries are fully charged. The relay gets 10 volts when the wait to start light is on. Then when clicking it jumps for 0 to 6-10 constantly. I checked my relay properly, that's the reading I got
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post #9 of 13 (permalink) Old 05-12-2019, 12:17 AM
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My batteries are fully charged. The relay gets 10 volts when the wait to start light is on. Then when clicking it jumps for 0 to 6-10 constantly. I checked my relay properly, that's the reading I got
OK. Batteries usually get above 13v after a full charge and settle down overnight to atleast 12.6v after full charge. If they are only getting 12 then they need to be looked at closer. Are you isolating the batteries by disconnecting (-) leads and testing voltage across the battery? Is each battery atleast 12.6v after sitting a night? Maybe worth getting a load test on your batteries. How old are they? Are they a matched pair?

You should not have clicking. When it is bouncing 0-6v then that suggests the rotating contact plate in the relay is not making steady contact.

When you tested your GPR, what was your voltage drop between the two large poles of the relay with engine cold, key on and engine off (KOEO)?

I see you recently replaced both GPR and all GPs so its more likely a battery or charging system or grounding issue but Relays can fail quickly. What brand parts did you buy?

The risk to GPs would occur if you were to cycle them for long periods so you should be OK.

Are you getting alot of white smoke at the tailpipe?


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Last edited by ArcticDriver; 05-13-2019 at 04:04 AM.
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post #10 of 13 (permalink) Old 05-16-2019, 06:08 PM
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This may seem kind of stupid, but please trust me, and try it.

Get some GOOD jumper cables, and connect them to another truck, and to this one.

Let the other truck idle for maybe 5 minutes. High idle is best.

Now, let your glow plugs cycle normally, and then try starting.

If it works, check your alternator and batteries. Mine seemed perfectly fine. Truck just WOULD NOT start. Crank and crank and crank. Cycle the brand new glow plugs, until even I was red in the face. Charge both batteries to full charge with a charger. Did this several times over about a week... No start. Jump it after letting it charge up from the other truck for 5 to 10 minutes... Started right up.

Try it. If it does work, first thing I'd look at is the alternator. It may be 'working'... Just not working well.

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Last edited by Selador; 05-16-2019 at 06:10 PM. Reason: additional info
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post #11 of 13 (permalink) Old 05-16-2019, 07:51 PM
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There is a small about 14GA. wire hooked to the glow plug side of the relay the one on my truck was yellow in color. Different year trucks might have a different color wire there. unhook that wire, and see if it starts. I did that to mine, and haven't hat THAT problem with it since.

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post #12 of 13 (permalink) Old 05-17-2019, 05:45 AM
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There is a small about 14GA. wire hooked to the glow plug side of the relay the one on my truck was yellow in color. Different year trucks might have a different color wire there. unhook that wire, and see if it starts. I did that to mine, and haven't hat THAT problem with it since.
What wire is the small yellow one?

Do you have a small orange also?

The small orange would be the PCM Control?


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post #13 of 13 (permalink) Old 05-18-2019, 05:48 PM
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I do not have a small orange. It might be the same wire, when I unhooked it, the short cycle at the end of the glow plug cycle stopped as well. Hasn't seemed to hurt anything, and I can have a couple of glow plugs out, without anything but a slightly longer crank period. I usually only replace the bad ones, so it doesn't hurt the pocketbook as bad as all at once. It was hooked to the relay itself, upstream of the resistance ribbon. Not sure if that's where it is supposed to be though. I bought the truck used and having to pull it to start, because the former owner didn't know what he was doing with glow plugs. There had been a lot of rednecking done to the poor thing, and I'm not above that myself, when necessary.

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