Glow plug relay issue
 

I had an issue with a truck not starting cold last year. Tested the GPR, and replaced it, it tested bad. After replacing the GRP, it still wouldn't start. The wait to start light worked, so I was thinking that everything was okay. I bench tested the GPR, it's definately good. So to start the truck right now, I just ran a ground to the GPR, and hold the button like an old time truck...and start after holding the button for 30 seconds.

I really want this thing to work on its own like it's designed to, does anyone have any ideas of what I might look into? It starts and runs great when I manually run the GPR, but I'm thinking it might be the pcm.

BTW, it's a 2001, 142k.

Your relay's might not have necessarily been bad. When you tested your GPR's, did you only check to see if power was being transmitted between the two larger posts?

Because you should only see 12v constant at one big post (closest to the passenger fender), and with the key on you should see 12v at both. Now with the key on, you should see 8v at the smaller post (closest to the firewall) and 8v at the other small post.

Your "wait to start" light is a good indicator that your PCM is good and GPC (Glow Plug Controller) is working properly. How long does the "wait to start" light stay on before shutting off? It should stay on for a minimum of a couple seconds (like 5 or so if it's warm out) and shut off after say 20 or 30 seconds (depending on temperature). But in reality, your glow plugs are commanded on for a minimum of 10 seconds, and up to 2 minutes depending on outside temperature (the "Wait to Start" light does not stay on for the whole duration).

I went through this EXACT problem on my buddies 95', (I wasn't seeing 8v at the two smaller posts) it was the GPC harness from the GPC to the GPR. :tu:

Key off, I checked the larger post that has direct battery voltage, it read 12.7. The opposite larger post read nothing. After turning on the key, checked the voltage again at both posts. They both read the same as before the key was on. That is what prompted me to replace the relay. I never did bench test the original one, as I was 99% sure it was bad. I took it off and tossed it in the dumpster.

But now that you mention it, I will have to test the truck's 2 smaller posts. I think I read somewhere that it was controlled by a ground signal sent to the GPR. That's what prompted me to run a wire to manually switch the ground.

With the key off, should I see anything at the 2 smaller posts?

Will repost on Monday and let you know what I find at the GPR for voltage again.

Thanks for the great info!! :choochoo:

No, you will not see any power on the smaller posts with the key off. You should see 8v supplied by the GPC with the key on, engine off OR running on both sides of the relay. (small posts)

A relay (if you don't know this already) is an electromagnetic switch. It uses a small, low amperage signal to control a high amperage circuit. The low amperage circuit being your signal from your GPC, using only 8v, controlling the high amperage circuit, being your 12v.

If you do not see 8v on the two smaller posts, it means that the signal from your GPC is not reaching the GPR to switch the relay on. If you can take test leads from your battery + and -, and touch them to the two smaller posts and the same time, and you see 12v appear on the other big post on the relay, your relay is fine.

I'm 110% sure the relay is good due to grounding the terminal and it working. I just need to reconnect the wire to the relay and disconnect the temporary switch I wored up to check for the 8v signal.

I'm guessing that one of the wires is probably corroded through as I've had nothing but headaches with electrical problems due to the previous mechanic probing wires for whatever reason, and not sealing the little hole he created in the wire's insulation. But I looked as much as I could, and could not see any bad wires at the time I was troubleshooting the problem. I was also under the gun to get the truck started because it was snowing and it's a plow truck...

Anyhow, more info tomorrow...

[QUOTE=ken_man_1;863920] I'm guessing that one of the wires is probably corroded through as I've had nothing but headaches with electrical problems due to the previous mechanic probing wires for whatever reason, [QUOTE]

THE "MECHANIC" WAS PROBING WIRES?!?!?!?!:s::scare2::argh::scare2::s::scare2:: ouch::argh::td::dang:

I'm sorry but the NUMBER 1 thing you learn with ANY type of electrical training is that you ABSOLUTELY DO NOT PROBE WIRES. for this exact reason:argh:

But to answer your question, yes. If you are manually controlling your relay and the glow plugs are working, then I'm pretty confident your harness from your glow plug controller to your relay is hosed.:tu:

Before I go totally nuts, where is the GPC? Then I can go in with an army instead of just a scout.:bat:

I will be honest with you, I am not 100% on 99-03 7.3's. Although I do belive it's on the passenger side of the top of the motor.

I'm more familiar with the "OBS" 7.3's where it is located under the dash (94.5-97)

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P0683 - Glow Plug Control Module? - Ford Truck Enthusiasts Forums

^ found it on google for ya:tu:

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and just my opinion, if the previous mechanic was probing wires, you might as well just order the harness from Ford or International. Chances are the one wire you need (if not more) are in the same condition. Just my 2 cents:c:

I hear ya. The issues I've run into were all on the driver side where the 4x4 relays are (shift on the fly), and of course, the trailer wiring. I've had to repair wires on many trucks he put his golden screw driver in. I've gotten most of the problems squared away, as I have good record keeping in place, and I've scoured his records and looked into everything he did. But I think if I get 1 more issue, I won't be repairing it with a sealed butt connector...:argh:

There is no glow plug controler on most 7.3's... Only the cali models and the excursions have a glow plug controler...

You have a glow plug relay.

There are two of them, one closest to the turbo is the glow plug relay, one closest to the front of the motor is for the intake air heater.

Make sure you replace the correct relay.

The WTS light has NOTHING to do with the glow plug relay, or controling the glow plugs.

It is an idiot light plain and simple.

CPIPSD is correct here, as my truck is a Wisconsin truck...no California emissions. What drives the GPR then? Is it the GEM Module? :s:

:argh: sorry about that giving you the wrong info there, my father has an excursion that I recently did a little work on so it was fresh in my head, and just typing it in google images probably just gave me a picture of an excursion. it's been a while :ouch:

The PCM controls the GPR in your case:jump:

And just FYI, the state you bought the vehicle in does not matter (unless you live in California). California emissions is just a standard (a more strict set of parameters), you can get a California emissions vehicle ordered and delivered to any of the 50 states. For example; a friend of mine bought a 95' F350 PSD from a company on the eastern side of CT. He was only the second owner, and the company bought the truck brand new. After looking at the truck for him after he bought it, I found the "Catalyst" sticker on the radiator support which says in bold print "California Emissions Equipped". -coming from a CT emissions inspector

No sweat DieselDanBoy, I can certainly understand the mixup. I looked and saw nothing there :P I'm on a witch hunt now, post back later. :bat:

Although I'm still confident it's a relay control circuit issue

Ran into this a time or two in my shop. First time it was the PCM that was faulty, second time it was wiring in the main harness leading up to the 42 pin connector not actually the engine harness.

Quick test is to pull the small wires off (so that one doesnt power the other thru the relay) and see if both have power when the key is turned on. If so then powers coming from the PCM and wiring good if not onto testing the harness

Find a good wiring diagram and then test resistance in the two activation wires from at the Glow Plug Relay all the way to the associate pin at the PCM plug at the firewall (pull the plug DONT PROBE!) is how I test them. If both wires are good then you're only left with a fault bus circuit in the PCM or a magical gremlin

Nice truck smokie, welcome too db and do you have any good schematics? or know where to get em?

New to posting so hope this works. Im attaching (or hoping to) acouple of my diagrams ones for pickups ones for excursion. Cant seem to find any of my info on the pin layout on the connectors tho. Ill keep looking

Very awesome :jump: Thanks for the info.

Now, here's what I've got.

Key off, no voltage at the GPR except for the 1 large terminal (Direct to battery).

Key on, voltage at same large terminal, and voltage at the small terminal toward front of truck (red wire), but no voltage at the other large terminal. Voltage at the other small terminal as well, but no activity on the relay. The other wire is orange, and when I ground that terminal (with orange wire off), the relay operates. So that leads me back to looking at the 42 pin connector for fault there or the wire itself (between the relay to the 42 pin connector). Is that connector on the driver side valve cover?

Thanks for the diagram as well. I love having an arsenal of info.

the orange wire is ground. maybe the ground is just bad?

PCM main hot comes to one small wire so it'll always be hot, cant remember which one. Other one is hot when the PCM doesnt want glow plugs then the PCM sends ground to activate. Did you unhook the wires from the relay when youre testing them?? IF not then one wire can power the other thru the relay coil and you dont learn anything from testing.

If both wires (tested while unhooked from relay) have power youre left with a bad PCM which happens or I think the oil temp sensor might play a roll in deciding if the glow plugs kick on or not but dont hold me to that.

Got a buddy that wouldn't mind lending you a PCM for a quick test??

-Jordan

I guess I need a good schematic. I see the one from a post earlier, but I'm not 100% sure I'm reading it right.

Orange wire is the one I disconnected, and use my manual ground button. The red wire has power at the relay.

Yes, I did remove the wires to test. The red has power when cold, but the orange does not. In fact, it doesn't even have continuity to ground when cold.

I know typically the pcm will trigger grounds. I just don't know here. It's weird that the pcm would command a ground for the GPR, then command 12v for the GPR to shut off. But I am not all knowing, that's why I'm here!!

i kinda thought that the pcm sent power to send the juice and the ground was not controlled.

I don't usually have to troubleshoot pcm problems on my Fords, only the Chevy trucks. I had an issue of injectors, and the pcm wasn't pulsing the ground for 1 cylinder. That's what I'm falling back on. I just thought that pcm's pulse grounds...but as I said before... I'm not all knowing...:c:

wiring is not my thing to be honest. but didn't you say there is no continuity between the relay end of the wire to the 42 pin connector?

I didn't check it yet. I need to find that connector. I had 10 minutes to run my testing before I had to move on to the more important things :dang:

I'm really good with wiring, just not up to par on this one...yet...

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I meant that there was no continuity of the orange wire to ground when the GPR should have been commanded to be on.

PCM uses grounds for activation on the relays and varying voltage on regulors (IPR valve, EBP valve, exc). no continuity sounds like a bad wire/pin in connector. Id pull both the 42 pin connector and the main at the PCM and to a continuity test all the way from the PCM to the relay and I bet you find the problem. The 2 bad PCM's that Ive ran into on this both were sending hot and just never sending the ground signal so since no hot pressent on both Im guessing wiring.

The PCM uses POWER AND GROUNDS to control your circuits (5v to most sensors). In this case you have a bad ground that IS NOT PCM CONTROLLED. The PCM provides power to your GPR to switch it on and off. A PCM cannot "send a ground signal" (because a ground is just a ground, no voltage), but it can open up a path to ground (this is not your case).
I will re-post where this ground goes to

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I've traced the wire (it's red or violet with an orange tracer) back to the PCM, so the circuit can have a constant PCM ground (unswitched).

Like someone said up here already you're gonna have to test the wire from the GPR to the PCM connector.

Ok, that sounds good on both posts. I didn't have time to check it today, maybe tomorrow. Where is the 42 pin connector at?

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Scratch that, I found it. Thanks for the great info, will post when I get more into it.

Then why is one wire always hot (power thru PCM from one of the two ignition fuzes)?:nope: PCM sends ground to complete circuit. There is no constant ground and wiring a constant ground will fry all 8 glow plugs. IH does this on a lot of things. Become a certified Navistar dealer and you'll learn this fast. The ground is the signal and is PCM controlled. That wire is your problem or the PCM itself isnt activating.

the only constant power is the one big post on the GPR. the two smaller posts on the GPR are PCM CONTROLLED. THEY ONLY TURN ON WHEN THE IGNITION IS ON. your 2 fusable links coming off your starter solenoid are only for the high amp side of the GPR.

your glow plugs are grounded in the cylinder head, therefor they have a CONSTANT GROUND.

again. there is no such thing as a "ground signal". the PCM can only provide a path to ground. IN THIS CASE you have a CONSTANT ground provided by the PCM, which is the same ground that EVERY SENSOR on this engine grounds to.

By ground signal, I mean the PCM activates a path to ground. Thats common PCL logic control used everywhere from manufacturing industry to aircraft to in this case automotive. Post activation switching (activation after the load) reduces the total wattage flowing thru the logic board thus reducing heat. But what would I know, only went to 6 years of schooling for electronics and Navistar International master tech certification and have an office full of diagnostic manuals direct from IH including the posted diagrams above. So unless IH decided to wire the powerstroke ass backwards from the DT444E, its a ground activation system.

Any yes that ground provided is the same ground as every other PCM supplied ground.

I think I need to clarify my "ground signal" so we don't have anymore disagreements.

When I said "ground signal", I meant that it switched the ground thru the pcm. Kinda like flipping a switch so to say.

I hope that makes sense. :s:

first off i have to say you guys are great. this is my first post... or question. i have a 97 F350 7.3 and i am having glow plug issues. i tested my plugs and then noticed that my gpr was not pushing the 12v though. 8 some volts (closest to the firewall) but i was getting 12 some closest to the radiator. then i read to disconnect and test. (Duh...) what was i thinkin... so then i get my 8v and nothing on the other. just now starting to track from there and i hope that someone can offer some direction. thanks

Jerry

Update...kinda late. I had to remove the turbo and a bunch of other things to replace the injector cups. While I had everything apart, I check continuity on the glow plug wire to the harness. Where the plug is just over the valve cover, there was continuity there. Past that, I just gave the wire a little tug. Guess what! It was loose. I then just split the wire loom and reattached the corroded wire. It now works as it should.

I had another one, same thing. Just in a different place.

Typically when you see reduced voltage, it may have something to do with corrosion somewhere. Even in the middle of the wire loom.

I just wanted to post the fix as I see a lot of people ask for help...fix the problem...and never post back what fixed it because...well...they got their fix and forget everything else. Forum only is helpful when a solution is found...and posted. :c: