Another glow plug relay question.

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Dec 17, 2005 | 07:16 PM

GB04

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Another glow plug relay question.

I have replaced my glow plug relay on my 2000 ford excursion, with part F81Z-12B533-AC (DY-861). It doesn't look the same as the one that it replaced. The one that was in it, appears to have an international part number on it 1831645C1. It's shorter and has a different mounting plate. However I can't find any parts dealer that says there is a different relay for a 2000 Excursion 7.3, than the one I purchased.
So I installed it and the relay still doesn't work. I turn on the key and I get power on the left large terminal and the 2 smaller terminals. The right large terminal does not get any power at all. The vehicle has been sitting for 7 hours in 25 degree temp.
What could possibly be wrong? There is no check engine light or diag codes.

Dec 17, 2005 | 11:06 PM

SpringerPop

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From: La La Land

The clue is that you have both small terminals with +12 volts on them. The one closest to the firewall should get pulled to ground by the PCM for a couple of minutes when the engine is cold, causing the relay to close for that time, supplying current to the glow plugs for that period. It shouldn't stay at 12 volts. It will return to 12 volts after the GPR has turned off again.

I wrote up a testing procedure with a photo of the relay. It's post #11 in thread:
https://www.ford-trucks.com/forums/s...d.php?t=426789

What is possibly wrong?

1) An open wire from the PCM (Powertrain Control Module, engine's brain) to the GPR.

2) Whatever causes the ground in the PCM is fried. This is likely a transistor wired open-collector.

3) One of the sensors that determine that the PCM should not trigger the GPR (because the engine's hot) is broken. Coolant temp sensor thinks engine is warmed up?

Remove the wire on the terminal closest to the firewall and jumper it to ground temporarily, like 60 seconds. Jump in and try to start the truck. Likely it will start now.

How to fix it:

Find an open wire. Time.

Find if there is an errant sensor. Time and money.

Replace the PCM. Lotsa' money.

Wire a push-button switch inside the cab to manually control the GPR. A few bucks and some time.

Go look at the other post.

Pop

Last edited by SpringerPop; Dec 17, 2005 at 11:16 PM.

Dec 18, 2005 | 12:11 AM

Kwikkordead

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From: Rio Rico, AZ.

Quote:

Originally Posted by SpringerPop

Wire a push-button switch inside the cab to manually control the GPR. A few bucks and some time.
Pop

I did that even though my GP system was performing flawlessly. I wanted to save on glow plug life.
Yes my truck smokes like a chimney on cold mornings unless I hold the switch down for a long time. It goes away within 5 minutes of fast idle, or 30 seconds of driving away. Yes I drive away with a cold engine, gently of course. It warms up the engine 10 times faster to operating temperature, which is really what we want. Operating temperature.
No I don't care if it smokes like that, it's a cold diesel engine! I want to preserve the life of the glow plugs.
Rant mode off.

Too much caffein today.

Dec 18, 2005 | 10:37 AM

GB04

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I believe I have solved my glow plug relay question(s).
A 2000 ford excursion with a 7.3 doesn't have a glow plug relay, it only has a glow plug controller (to meet california emissions). The relay I was trying to replace was my IAH relay.
Being that I don't have any OBDII trouble codes, my glow plug system must be working, or it would be throwing codes according to the documentaion I have read.
So I guess it must be normal for a 5 year old diesel to smoke like crazy on cold morning start-up. I don't remember it being that bad though...
What is comes down to is this. Even though every auto parts store will sell you a relay for a 2000 excursion, you probably don't have one. The easiest way to tell is to look for a rectangular silver box with a heat-sink exterior behind the IAH relay. If you have one, that is what controls your glow plugs.

Dec 18, 2005 | 10:55 AM

Kwikkordead

Fleet Owner

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From: Rio Rico, AZ.

GB04 you most likely have one or more glow plugs that are burned out. The engine is still firing ok on the remaining cylinders. The smoke is coming from the cold cylinders not firing.

Dec 18, 2005 | 11:09 AM

SpringerPop

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From: La La Land

I think it was Cookie that posted the complete wiring diagram for the CA emissions glow-plug system, just last week. You must have missed it.

The search function will find it for you.

Pop

Dec 18, 2005 | 12:23 PM

GB04

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Quote:

Originally Posted by Kwikkordead

GB04 you most likely have one or more glow plugs that are burned out. The engine is still firing ok on the remaining cylinders. The smoke is coming from the cold cylinders not firing.

Thats the strange part. According to the information I have read, the glow plug controller is supposed to identify any of the 8 glow plugs that may be bad. All the way down to resistance that is out of spec, or a dead glow plug.
I did test 4 of the glow plugs and they were perfect.
It starts real easy, and idles good for a cold engine. It just smokes for about 3 minutes on start-up.