Weird Glowplug Resistor Bypass Issue

[LastFbody]

So I bypassed the glow plug resistor like has been outlined many times by other users. Just tried it with the original gp relay just to see what would happen, and maybe save a couple bucks if it worked. It seemed to work kind of at least. The glow plug relay and wait light kick on with the key as usual, and the truck starts right up with no drama. What has changed is the stock voltage gauge that used to read on the border between green and the upper red now reads in the mid green. The other thing that changed is the afterglow didn't engage at all, and it almost always did before in the garage, which is usually about 50 degrees.

2 questions that aren't mutually exclusive:

1. My garage was about 50 degrees ambient. The truck always used to run the afterglow 3-4 times at that temp. May have been running incorrect before due to electronic space magic and is now running correctly. My one truck is my only frame of reference, when is the afterglow supposed to engage normally?

2. Glow plug relay issue? Heard that sometimes after being hooked into the stock resistor system for however long that they won't get enough juice under straight 12v to kick on. Could it turn on for the primary glow cycle and not be able to turn on for the afterglow cycle?

Edit: According to this thread (specificly Antennaclimber's posts) https://www.steelsoldiers.com/showt...ystem-Dilemma-AntennaClimber-this-is-for-you-) the afterglow cycling on and off after startup that I've become familiar with is due to the gp card recieving more than 12.5v, and if it recieves 12.5v or less the afterglow is steady. Can anyone confirm this threads claims as accurate?

 

[LastFbody]

https://www.steelsoldiers.com/showt...ystem-Dilemma-AntennaClimber-this-is-for-you-)

The answers in this thread sound well researched. I always had the impression that the afterglow cycling on and off was entirely based on how cold the engine was and nothing else. This thread says it's due to the glow plug card noticing more than 12.5v going into the gp's and turning the power on and off to save them.

Is their explanation the gospel truth? Is the cycling afterglow all about protecting the gp's?

 

[Tinstar]

The afterglow is to keep temps in cylinders up until sustained combustion is assured.
When it’s really cold outside, engine has a chance of stalling and quitting without afterglow.

 

[LastFbody]

The afterglow is to keep temps in cylinders up until sustained combustion is assured.
When it’s really cold outside, engine has a chance of stalling and quitting without afterglow.

Right. I get that. What that other thread is saying is that the cycling on and off only happens due to excessive voltage, and if there's 12.5v or below the gp's just stay on steady for the afterglow.

I didn't differentiate between the supposed steady afterglow as detailed in the other thread and the cycling afterglow. Sorry for the confusion.

 

[Barrman]

The CUCV afterglow normally happens without turning the light on. All of mine never have the light come back on after engine start. However, watching the volt meter I can see it is happening. Duration depends on temperature as mentioned above.

The CUCV volt meters are not very accurate. I have had several in one of my trucks due to finding other used ones that have better preserved faces and lenses. They all read different levels of voltage on the scale at different points in the operation of the truck.

I would suggest you get a digital volt meter, check the batteries with the engine running. 14.4 volts per battery for 28.8 volts on the system is what you should have. If you do, make note of where the needle on the dash gauge is and drive on with that as your new standard operating spot.

 

[cucvrus]

May I ask why you eliminated the resistors? I have them on 10 trucks and they have worked perfect and the voltmeter cycles as designed. The stock voltmeter as you know has no numbers but a small check up top of the green to indicate good charge. Good Luck. Switch it back or fix the original problem that caused you to switch. It will function again as designed then the statement read the TM's is good advise. Have Great Day. Time to take the plows off and get the transmission overhauled in the salt spreader truck. As Rustystud advised I will request a Kevlar reverse band. I have allotted $2500. for this repair. Do it right the first time or don't do it.

 

[LastFbody]

So all of your trucks have the glow plug resistor bypassed?

If so, what are the approximate temperature thresholds that the afterglow kicks on? Prior to this mod mine used to cycle afterglow 3-4 times seemingly regardless of ambient temp on every first startup. On startups after the engine got to temp the truck fired with no wait light or glow plug activity. Pretty much what I would expect. What I'm trying to figure out is if my truck was running normal before and its screwed up now, or vice versa, or if this is just normal behavior for a truck with the resistor bypassed to straight 12v.

My wait light never comes on after startup, I always paid attention to the voltage gauge needle and the clicks of the glow plug relay like you're saying.

 

[Bighorn]

I started mine at 16f this morning.
I have the resistor bypassed.
After a wait light for 15 seconds, my glow plug solenoid was still engaged according to my volt meter.
I turned the key with half throttle and it started right up.
Got one after glow out of it about 3 seconds long.

This winter i started it at minus 20 without block heat.
Got 3 full after glows of 3 seconds each.

Sometimes no after glow at all.
Depends on temp and voltage.

Ps. Cucvrus is Mr. Resistor.
Someday the feds are gonna raid his house and be puzzled by the mountain of strange tubes.

 

[LastFbody]

There wasn't a glaring problem that caused me to bypass the resistor pack. Supposedly with the resistor pack setup if you have a glow plug fail it will ramp up the voltage slightly on the remaining 7, until the next one fails, then the voltage goes even higher on the remaining 6, and so on. Wanted to avoid the potential for cascading failure.

Kevlar reverse band..?

Edit: Ah, you're talking about a different project.

 

[LastFbody]

I started mine at 16f this morning.
I have the resistor bypassed.
After a wait light for 15 seconds, my glow plug solenoid was still engaged according to my volt meter.
I turned the key with half throttle and it started right up.
Got one after glow out of it about 3 seconds long.

This winter i started it at minus 20 without block heat.
Got 3 full after glows of 3 seconds each.

Sometimes no after glow at all.
Depends on temp and voltage.

Ps. Cucvrus is Mr. Resistor.
Someday the feds are gonna raid his house and be puzzled by the mountain of strange tubes.

That sounds exactly how my truck is behaving right now. It seems to work well enough, its just different from how it was before.

 

[LastFbody]

So I took a reading at the glow plugs with the bypass, the truck doesn't stop the afterglow for a crazy long time. I shut down after 20 seconds of straight afterglow. It may be a question of the original glow plug relay not being able to turn off with straight 12v. I decided I'd rather take my chances with the resistor pack.

So that's all hooked back up, and the glow plugs shut off after a reasonable amount of time and are getting 12v or under for primary glow, and get ~13v flipping on and off for afterglow. I'll just check it periodically.

 

[Bighorn]

You know.
Mine probably operates differently.
I totally converted to 12v.
Both batteries in parallel.
So my gp cards voltage sensing is gonna be different than just hooking one battery up.
Course, plenty of folks here run them like that.
I am in the minority.

 

[LastFbody]

Thing that was scary about the afterglow with the bypass was that it didn't really show a power draw on the voltage gauge, but it was absolutely sending power to the glow plugs.

It might just be my specific truck due to the electronic space magic weirdness that surround cucvs, but it might be worth checking with a multimeter when the glow plugs actually shut down. It scared me right off of the 12v bypass with how long they run.

 

[Bighorn]

Then again, consider that millions of civilian Chevrolet and GMC pickups and Blazers had 6.2 diesels.
All of them 12 volt.
The glow plug card is 12 volt.
The glow plugs are 12 volt.
The only reason for the resistor is to have 24volts avaliable for the Nato slave plug but still play nice with the rest of the truck which is and was designed to be ;12 volt.
The 24 volt starter was neccesary, not desired.

I think you have some other issues in your system.
There should be no problem running the gp solenoid on one battery.
But cucvrus would be glad to send you another resistor bank in exchange for some license plate, should the need arise.
Consider this, despite the luck of some folks, there have been cascade failures due to defective 30 year old resistors.
Have fun with that.

 

[LastFbody]

See, this is something that I've seen/had happen to me from day one on this forum that I really don't understand. Whys everything gotta be so darned personal on here?

I'm not crapping all over what works best on your truck(s), if it work's on yours and your glow plugs shut down properly, then awesome, I'm happy that your rig(s) work and there's a couple more trucks that are being cared for and staying on the road. It just didn't work on mine for xyz reason and I had to go back. I'm not out to please or displease anyone, I only go after what's objectively the best answer.

I appreciate the input I got on here, I learned a couple of new things.

 

[Bighorn]

You said it.
Cosmic space magic.
Cucv's aren't just GM trucks.. only the TMs contained here can decipher their mystery.
Normal automotive principals go out the window.
At the beginning of time there was the CUCV and billions of years later GM designed the civilian version.

 

[rsh4364]

I have had really good luck with just push button glow plug activation.

 

[MarcusOReallyus]

Edit: According to this thread (specificly Antennaclimber's posts) https://www.steelsoldiers.com/showt...ystem-Dilemma-AntennaClimber-this-is-for-you-) the afterglow cycling on and off after startup that I've become familiar with is due to the gp card recieving more than 12.5v, and if it recieves 12.5v or less the afterglow is steady. Can anyone confirm this threads claims as accurate?

https://www.steelsoldiers.com/showt...ystem-Dilemma-AntennaClimber-this-is-for-you-)

The answers in this thread sound well researched. ....

You can bank on it. Nobody knows more about the GP system on these trucks than Antennaclimber. He has a business building replacement GP controller cards. That particular project is the result of his knowledge of the system.

 

[Tinstar]

The stock system works as designed.
For whatever reason, some guys convert to 12v, install push buttons, etc.
If it works for them....Great!!
Their truck......Their rules.

I prefer the stock system.
Have had a cascade GP failure due to broken tips on three plugs.
Didn't discourage me one bit.
Replaced Glow plugs and GP solenoid.
Back to running like a champ.

The trucks require a lot of maintenance regardless of what’s done to it.
Just a fact since their old.
I would rather maintain a stock system than a modified/converted one.


Glad you sorted out your issue

 

[LastFbody]

The stock system works as designed.
For whatever reason, some guys convert to 12v, install push buttons, etc.
If it works for them....Great!!
Their truck......Their rules.

I prefer the stock system.
Have had a cascade GP failure due to broken tips on three plugs.
Didn't discourage me one bit.
Replaced Glow plugs and GP solenoid.
Back to running like a champ.

The trucks require a lot of maintenance regardless of what’s done to it.
Just a fact since their old.
I would rather maintain a stock system than a modified/converted one.


Glad you sorted out your issue

Seems to me that every one of these trucks are just a little bit different with how they behave electronically, and that there's no single perfect ideal solution for most things.

Going back to the resistor was kind of a 'go with the devil you know' decision. It probably won't be an issue if I break out the multimeter and check it every now and again. That being said, it's true that all the resistors are 30+ years old. Has anyone found a suitable currently produced replacement for if and when it takes a crap? I know theres ways to drop 24v to 12v, but not sure if theres something out there suitable for engine bay heat like the original.