CUCV early Glow Plug burn out - What is the cause?

Commander5993 · Jan 9, 2025

Hey all, I've went through 3 sets of AC Delco 60G glow plugs in the last four years. I know the CUCV can be hard on plugs, but this is not normal. But I can't find the issue. I know if one or more plugs burn out, then the rest get over voltage. But I shouldn't even have the first plug to burn out in just a year. I replaced them early last winter due to the same reason. All work fine for a while, until they don't. $90 a set is getting expensive. Anything I should be looking for??

Any Suggestions or Advice Appreciated

WWRD99 · Jan 9, 2025

Commander5993 said:
Hey all, I've went through 3 sets of AC Delco 60G glow plugs in the last four years. I know the CUCV can be hard on plugs, but this is not normal. But I can't find the issue. I know if one or more plugs burn out, then the rest get over voltage. But I shouldn't even have the first plug to burn out in just a year. I replaced them early last winter due to the same reason. All work fine for a while, until they don't. $90 a set is getting expensive. Anything I should be looking for??

Any Suggestions or Advice Appreciated

I'd say there's 2 main things that'll do that. If you have the resistor still hooked up, it could be giving more than 12 volts to them. Second is the single wire temp sensor, or double if it's been changed, could be broken or the wire is not giving resistance to the glow plug card, making the glows turn on for the maximum amount of time plus the long 3 after burns. Either one is pretty easy to find with a basic dvom hooked to the output of the glow plug relay. You'll see the volts and how long they're on. You should also see the glow plug after burn on the voltage gauge going low when they turn on. I've used 60gs for years and do replace every 2 years just because I'd prefer to keep the truck starting in cold weather and not replacing them when it's 15 out.
How cold does it get where you are?
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Commander5993 · Jan 9, 2025

WWRD99 said:
I'd say there's 2 main things that'll do that. If you have the resistor still hooked up, it could be giving more than 12 volts to them. Second is the single wire temp sensor, or double if it's been changed, could be broken or the wire is not giving resistance to the glow plug card, making the glows turn on for the maximum amount of time plus the long 3 after burns. Either one is pretty easy to find with a basic dvom hooked to the output of the glow plug relay. You'll see the volts and how long they're on. You should also see the glow plug after burn on the voltage gauge going low when they turn on. I've used 60gs for years and do replace every 2 years just because I'd prefer to keep the truck starting in cold weather and not replacing them when it's 15 out.
How cold does it get where you are?
Sent from my SM-S906U using Tapatalk

Hi WWRD99 appreciate the info. Temps here as of late, have been in low teens at night. 20's during day. But it supposedly got above freezing today, although I didn't see any ice melting. But I went to drive the truck a week or so ago, and it had only been like 30's that previous night, and I had a time getting the truck started. Cranked just fine, but didn't want to hit. Had to feather the "gas" pedal and finally got it to stay running, once it warmed up it was fine for the rest of day doing errands and hauling some lumber. Smoked a good bit at first because of not burning all the fuel.

I didn't know the "norm" life was only 2 years

I thought it should have been a lot longer. So idk, maybe I'm not getting to much worse than normal I guess.

I'll have to check about the resistor, as I can't remember. I do know I've tested the voltage before, but can't remember the details now.

I do also know that the temp sensor isn't working. Back a year or so ago, as soon as I would start the truck, the temp light begins to glow. As the truck warms up the light goes full brightness. But for no apparent reason, the truck is not overheating at all. (I had a thread about this on here somewhere back then) I replaced the temp sensor once, same issue. After some months I replaced the sensor again last year with an AC Delco brand I believe, but it still did the same thing. But I never could figure out why. I got tired of seeing the light, and since it was just always on that doesn't tell me anything. So I unplugged the sensor with the intent to upgrade my actual temp gauge in the truck. The one I currently have shows cooler temp than it actually is, but it still gives me a general idea.

With that said, I did not know that the temp sensor also controlled the glow plug card. Should have thought about that though

I do have a GP manual override safety switch that I could use (after replacing plugs) but would have to unplug the card though. I installed the manual switch not long after I got the truck back about 13 years ago, as a "just in case" measure. As I had read at the time about guys having issues with the cards. But I've never used it other than testing. I've always just let the card do its thing.

I'll have to pull these plugs when I can get the truck into my barn. not going to try to start it now, as it has been in low teens at night this week. Supposed to be getting 5 to 7" of snow tonight now. Hope I don't need to go anywhere for a few days. I live out in rural farm area, and it takes the little towns around here a good while to ever get the roads decent, as they only have a few plow trucks and don't hardly use any salt.

I'll test each plug and keep the "good ones" for spares. I ordered another set of AC Delco's from our local auto parts store, supposed to be in tomorrow.

Thanks for the info WWRD99 [thumbzup]

this gives me a place to start to troubleshooting and go from here

WWRD99 · Jan 9, 2025

Commander5993 said:
Hi WWRD99 appreciate the info. Temps here as of late, have been in low teens at night. 20's during day. But it supposedly got above freezing today, although I didn't see any ice melting. But I went to drive the truck a week or so ago, and it had only been like 30's that previous night, and I had a time getting the truck started. Cranked just fine, but didn't want to hit. Had to feather the "gas" pedal and finally got it to stay running, once it warmed up it was fine for the rest of day doing errands and hauling some lumber. Smoked a good bit at first because of not burning all the fuel.

I didn't know the "norm" life was only 2 years
I thought it should have been a lot longer. So idk, maybe I'm not getting to much worse than normal I guess.

I'll have to check about the resistor, as I can't remember. I do know I've tested the voltage before, but can't remember the details now.

I do also know that the temp sensor isn't working. Back a year or so ago, as soon as I would start the truck, the temp light begins to glow. As the truck warms up the light goes full brightness. But for no apparent reason, the truck is not overheating at all. (I had a thread about this on here somewhere back then) I replaced the temp sensor once, same issue. After some months I replaced the sensor again last year with an AC Delco brand I believe, but it still did the same thing. But I never could figure out why. I got tired of seeing the light, and since it was just always on that doesn't tell me anything. So I unplugged the sensor with the intent to upgrade my actual temp gauge in the truck. The one I currently have shows cooler temp than it actually is, but it still gives me a general idea.

With that said, I did not know that the temp sensor also controlled the glow plug card. Should have thought about that though
I do have a GP manual override safety switch that I could use (after replacing plugs) but would have to unplug the card though. I installed the manual switch not long after I got the truck back about 13 years ago, as a "just in case" measure. As I had read at the time about guys having issues with the cards. But I've never used it other than testing. I've always just let the card do its thing.

I'll have to pull these plugs when I can get the truck into my barn. not going to try to start it now, as it has been in low teens at night this week. Supposed to be getting 5 to 7" of snow tonight now. Hope I don't need to go anywhere for a few days. I live out in rural farm area, and it takes the little towns around here a good while to ever get the roads decent, as they only have a few plow trucks and don't hardly use any salt.

I'll test each plug and keep the "good ones" for spares. I ordered another set of AC Delco's from our local auto parts store, supposed to be in tomorrow.

Thanks for the info WWRD99 this gives me a place to start to troubleshooting and go from here

Just to clarify the temp sensor that turns on the wait light is different than the one that turns on the low coolant light. The one to look for is on the rear of the drivers side head....way back by the vacuum pump. The manual switch if you did a ground to the 3rd wire on the glow plug card harness you can use that with the card installed. I assume you have a gauge for the temp that isn't stock? Yes glow plugs should last a good bit. I wouldn't want to change them that much since I have 4 of them. Glow plugs have almost doubled in price the last couple years. I didn't know it got that cold in Mo!! That's as cold as Pa is right now except we don't get snow anymore.

Barrman · Jan 9, 2025

Preventive maintenance wise changing the glow plugs when you live some where with expected 0° nights is a pretty wise choice every 2 years. As pointed out Doug it sure beats doing it on a cold dark rainy night.

The rest of us though can normally get 5-10 years or more out of a set of 60G glow plugs. But, the first time you get a puff of start up smoke with a stumbling engine that clears in a few seconds. Start thinking glow plug change.

Commander5993 · Jan 29, 2025

WWRD99 said:
Just to clarify the temp sensor that turns on the wait light is different than the one that turns on the low coolant light. The one to look for is on the rear of the drivers side head....way back by the vacuum pump. The manual switch if you did a ground to the 3rd wire on the glow plug card harness you can use that with the card installed. I assume you have a gauge for the temp that isn't stock? Yes glow plugs should last a good bit. I wouldn't want to change them that much since I have 4 of them. Glow plugs have almost doubled in price the last couple years. I didn't know it got that cold in Mo!! That's as cold as Pa is right now except we don't get snow anymore.

Yep, we have some cold weather at times during the winters here. Used to live in Indiana, in fall of 2013 I was looking forward to moving this far south... but the winters followed us

One guy we knew at the time when we first moved here, said that winter was the worst he'd seen in 35 years. Well, it hasn't really changed since then. Two years ago we had a very cold and snowy winter. Everytime one snow would finally melt off, the next one came in. Usually 6" to a foot with each one which is a lot for here. It was in teens, single digits, and below zero for sometime, along with high winds at times.

But this winter hasn't been as bad. It snowed about 6" here back 3 weeks ago or so. Just now in the past couple days did it finally finish melting off. And yes, we do have some warmer days. This week is the first week since winter set in that it warmed back up to what used to be "normal average" temps here. 50's and its even supposed to be 62 today and maybe similar saturday (after 2 to 4" of rain friday). But then it supposed to go back to the 30s next week or so. They were giving more snow to come in, don't know if they've changed that forecast or not. Going to get these plugs changed before then just in case I need the truck for that. I'll have to look into that resistor, can't remember if I have looked at that before or not. My memory isn't too good.

Commander5993 · Jan 29, 2025

Barrman said:
Preventive maintenance wise changing the glow plugs when you live some where with expected 0° nights is a pretty wise choice every 2 years. As pointed out Doug it sure beats doing it on a cold dark rainy night.

The rest of us though can normally get 5-10 years or more out of a set of 60G glow plugs. But, the first time you get a puff of start up smoke with a stumbling engine that clears in a few seconds. Start thinking glow plug change.

Yeah, I usually keep a set of plugs on hand. But used my last set last year. And hadn't bought another set until the other day. Just wasn't expecting to have to replace them already. And yeah, I'm not working on it out in the cold these days. My un-heated insulated pole barn stays about 50 in the winter, and thats cool for me when I'm going to stay over there working. Can't get my truck in there right now though, don't' have the room. Thought about changing them outside today, even though I have some other things I need to do.

Commander5993 · Feb 2, 2025

Hey All, Finally getting to my truck today while its warm. Supposed to be 64 today! And 72 tomorrow!! WOW what a difference.

Anyway, here is what I've found so far this morning. I pulled all the old plugs, they look fine, no bad build up or anything. Installed all the new plugs after testing them to make sure they're all good. Like we all know, just because parts are new doesn't mean they actually work.

However I did find one plug where the wire had been pulled off. The wiring harness on the passengers side was putting a little bit of tension on the plug wires. So I zip tied it up to the hard lines on the fuel rail. Now there is no tension on any of the wires.

That plug being disconnected is likely what caused others to burn out. I haven't tested the old one's yet to see how many are bad, but will do so shortly.

With that said, I run a voltage test and I am only getting 10 volts at the GP wires. I'm pretty sure it should be 12v shouldn't it?
Could the resistor still be connected and cause a low voltage like this? Stupid question, I've tried to find photos on here searching some threads but didn't come up with anything definitive. Where is the GP Resistor located or what does it look like...? I can't remember if I have already disconnected that in the past or not

EDIT: I already tested batteries, they are both at 12.5 with engine off. Haven't started truck today.

Commander5993 · Feb 2, 2025

Ok.... I'm even more perplexed now. I just tested all the old plugs, and ALL of them Lit up. I tested them like CucvRUS told me to back several years ago. Take plug, use jumper cables to a battery, place ground clamp around plug, dip tip of plug in oil, touch spade connector on plugs terminal to positive jumper cable clamp for about 1 second, see if the oil smokes. And All of them did.... so... now I'm not sure whats going on...

EDIT: I just tried to start the truck, first time it hit a little bit. 2nd time it hit a few times then fired up and immediately died. The 3rd & 4th time was about the same. I quit trying. Cranks over quickly though, so not battery or starter. Which I just replaced the starter with brand new Delco gear reduction last winter.

This is exactly like it acted a couple weeks ago, which I did get it running that day after 5 or 6 times, and it drove/started fine the rest of that day. But since I now know all the plugs are good, now, to me at least, it sounds like a fuel issue... ??

I put a new (rebuilt?) Stanadyne fuel injector pump on it just a few years ago, my memory isn't good but I think that was $400 or $600. And I replaced the lift pump a couple years before while doing other work. Going to check fuel filter, but I replaced it last year I think. I'm stumped at this point.

EDIT 2: Well I opened vent on fuel filter, and there was some pressure. It bled it off into the drain hose, seemed like there was some air too. So I pulled the pink wire off the injector pump and cranked the engine over a few seconds. Then went and closed vent on fuel filter and reinstalled pink wire. Tried to start it a couple more time, and it did fire up. But I had to feather the gas for a few seconds, and the engine was surging for about 30 seconds or so before it leveled out. It did that back two weeks ago too, but i figured it was because the cylinders with bad GPs were just cold. But since all GPs were good.... idk.

I have it running right now, idle dropped down and everything. Other than a pulley squeaking (i think its the pass alternator), its running smooth. I did dump some Heat water remover in the fuel tank along with some Stanadyne fuel lube conditioner. I'm wondering if i got some bad diesel. I'll shut it off in a bit and try a restart. Then shut it down and try it tomorrow.

m1010plowboy · Feb 2, 2025

I battled with a similar problem in the 1010 then some SuperDave guy replaced an $8.00 relay under the hood that made the glow plugs glow again.

Mostly parked indoors, we did have a few cold starts at altitude. Once things are volted and working correctly, cold starts should never be a problem.

Commander5993 · Feb 2, 2025

m1010plowboy said:
I battled with a similar problem in the 1010 then some SuperDave guy replaced an $8.00 relay under the hood that made the glow plugs glow again.

Mostly parked indoors, we did have a few cold starts at altitude. Once things are volted and working correctly, cold starts should never be a problem.

I never had any issue before this, except last winter which was fixed when I replaced my Glow plugs at that time. Thats why I originally couldn't understand why they were bad already. But found out today that they weren't bad. So i'm not sure whats going on now. Unless I'm missing something, it must be a fuel issue.

WWRD99 · Feb 2, 2025

Commander5993 said:
I never had any issue before this, except last winter which was fixed when I replaced my Glow plugs at that time. Thats why I originally couldn't understand why they were bad already. But found out today that they weren't bad. So i'm not sure whats going on now. Unless I'm missing something, it must be a fuel issue.

Sounds like the glows are working, but got an air leak now. I put clear fuel line on the return output on top of the ip. You'll be able to see the air bubbles going through it if there is. Oh and just because you replaced a part last year doesn't mean they're working now. I use as many nos original parts I can find...even if they're 20 plus years old. The lift pumps I use are surplus from 2003. If you find air at the ip check the box filter area for a fuel leak or the rubber hoses.

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Commander5993 · Feb 2, 2025

WWRD99 said:
Sounds like the glows are working, but got an air leak now. I put clear fuel line on the return output on top of the ip. You'll be able to see the air bubbles going through it if there is. Oh and just because you replaced a part last year doesn't mean they're working now. I use as many nos original parts I can find...even if they're 20 plus years old. The lift pumps I use are surplus from 2003. If you find air at the ip check the box filter area for a fuel leak or the rubber hoses.

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Well, i had used some nos. but some of it just didn't last, especially anything with rubber.

I'll have to look some more, see if there is air getting in somewhere or if its something else. I just thought... if there is air there might also be a leak... i might try my black light tomorrow and see if anything shows up.

Commander5993 · Mar 5, 2025

WWRD99 said:
Sounds like the glows are working, but got an air leak now. I put clear fuel line on the return output on top of the ip. You'll be able to see the air bubbles going through it if there is. Oh and just because you replaced a part last year doesn't mean they're working now. I use as many nos original parts I can find...even if they're 20 plus years old. The lift pumps I use are surplus from 2003. If you find air at the ip check the box filter area for a fuel leak or the rubber hoses.

Sent from my SM-S906U using Tapatalk

When it warms up, I'll use a clear hose on the IP like you said. And I may order a lift pump too, can always keep it on hand if not needed now. I last replaced it around 13 or 14 years ago. Its a pickle to get the bolts started when reinstalling if i remember right. It was an ACDelco 43254 from Amazon, but they're sold out or don't carry them anymore now.

TechnoWeenie · Tuesday at 6:34 AM

The CUCV has multiple things working against it when it comes to glow plugs.

1.

The power comes from the 24V bus across a large resistor on the firewall. This resistor, in combination with the ~.5-1 ohm resistance of ALL 8 glow plugs drops voltage to around 10-12V.

These glow plugs are in parallel with the resistor on the firewall.

Theoretically, the resistor is large enough to maintain 10-12V even with half the plugs failed - reality is, with inrush current and voltage spikes, too often it's the plugs that take the brunt of the impact.

2.

The OE plugs were OK but not stellar - Once failed they were often not replaced or the person tried the 'throw parts' at it method. The majority of the trucks I've seen for sale by fire departments and other government agencies were being sold because of issues with their glow plug systems. AC13G were the original plugs. AC60G plugs have better self-regulating than the Welleman or the AC13G, and do not swell, however they are not as high current and do take a little bit longer to get to temp. This is a positive in my eyes, as it means it's more reliable, and if glowing for 20 seconds instead of 15 is an issue for you, welll.. I don't know what to say.

3.

The glow plug controller and/or relay could fail 'on' and keep glow plugs on - killing them and the battery - - I had this happen personally actually. The glow plug card will sense low temp - run through a cycle - notice it's not heating and repeat attempting to heat. It's supposed to have a timeout if temp doesn't increase - and if temp does increase it will go into afterglow - a temporary on/off of the plugs to maintain heat while it's warming up - however my M1010 with 19K miles on it and near new inside was left at a shop who left it in RUN - destroying all 8 brand new glow plugs - literally put them in less than a week prior - because it repeated the glow cycle until the batteries were dead.

My original idea was to just switch to 24V HMMWV glow plugs, but AFAIK the only ones available are (S)Welleman, or knockoffs of, and none are very reliable, on top of the connector being impossible to find.

All my CUCVs have gotten a push button mod, a new glow plug RELAY, AC60Gs, and direct wire to 12V. I have not had any glow plug issues on any of my CUCVs with that setup.

TechnoWeenie · Tuesday at 9:43 AM

CUCV early Glow Plug burn out - What is the cause?

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