Glow plug relay? Or controller? Short cycle

[Subourbon]

Hey guys n gals,

1982 k20 suburban 6.2 diesel automatic trans. Th400 with overdrive.

I've made this a bit of a long post because i crammed it with history and details, and questions, figured that would me get clearer answers than
Glow plugs no work, help.

So the glow plugs give me a hard time,
I changed 7 out of 8. The 8th one snapped in half coming out and the other part is still in there. Gonna have to get an easy out and get that guy out. But when driving, the glow plug light (GP) comes on. Weird, I thought it only comes on for the start and maybe the first few minutes of running to maintain a certain temperature when it's cold out.

But no, she's plenty warm enough, been running for a while and still, it comes on.
When it does come on, if I'm coasting or at a light, it's all good. If I press down on the accelerator, it's makes this infernal belt screeching racket. (Side note, I checked the belts, they're good, right, plenty of bite left). But when the GP goes out, back normal running (I have to lift off the accelerator, and back on it again otherwise the noise seems to continue).
That's really weird!
Fast forward to October 2021, driving along GP come on do their screeching noise, and light goes out, but the truck died on me. I dont know if it is related to the GP light issue, because it happened about 8 more times on my drive, GP light on and light off. I pulled over, park. Starts right up again, no fuss. So can't be the battery. (Not fuel either I was full, and it didn't sputter or hard start).

Fast forward again, I plugged it in (quebec winter are cold) and decided to give it a shake down, died on me again, started right back up. But then as I'm parking (backing into my driveway) the GP light flashes on n off like a turning blinker only faster, I hear the relay clunk clunk clunk (mounted on driver side fender, next too windshield washer bottle).
What is happening here! Then yesterday I decided to run it up again to see if it was intermittent. It cycled fine the first time, then when I tried to start, I had this weird sort of grinding noise, like maybe the starter gear turning, but solenoid not throwing it, so it's just doing nothing, turning in its housing instead of grabbing the flywheel.
It was very cold out though.
I gave the starter some light taps with the end of a broom handle to see if it was jammed, when I say light I mean light, I don't wanna break anything...

So to summarize
1. GP light comes in when engine running.
2. Screeching belt noise when GP light on, stops when GP goes off.
3. Engine dies, with or without GP light (fires right back up though)
4. Clunk clunk clunk like a blinker, GP relay acting up.
5. Starter grinding noise (I suspect it stays in it housing turning because there is no sign of life from the engine)

Questions:
Glow plugs shouldn't turn on when engine is warm at all, am I right?

Could the belt screeching noise be caused by the broken 8th glow plug I mentioned? They're AC delcos, just to mention that.

Could the GP electrical issue cause the engine to die? Sometimes when in park to warm it up a bit, I give the accelerator some taps (light) and it'll kill the engine too, start right back up. I know 6.2s are slow and gradual, and I shouldn't Rev jt at all in park.

Clunk clunk clunk, would that be a relay issue? Because I figured out that the GP relay is the piece on the fender, there's also the GP controller which is tucked between firewall and engine block (sort of behind the air cleaner area). Is this something that has happened to any of you, is the relay the issue or the controller? Evidence seems to be pointing at the relay from my findings... I hear it's not uncommon to replace either.

And lastly, would the clunking blinking GP relay lead to the starter not throwing? Since I believe the batteries divert power to the GPs upon turning the key , once their cycle is complete, then power goes to the starter motor for start up of the engine. 12v system.
Or is a proper cycle of the GPs necessary for starter to work properly, like a start permissive or "interlock" if you will. Because i dunno bout all that being around in the 80s.

Anyways, if you made it this far, I appreciate you taking the time to read. I did some youtubing to seenifnother reported the same issue but, seems to be very popular to put a manual GP switch instead of the stock OEM one, if you want to leave your thoughts on what you guys have and if its worth the switch, I'd love to hear your thoughts!

Thanks everyone,

 

[Itali83]

I can answer a few questions now. First No, the glow plugs should not cycle after the first minute or so from a cold start. The screeching sound you’re hearing when they come on is the alternator belt slipping. The glow plugs are a huge amperage draw and an instant draw too. It’s causing the alternator to work hard enough to slip the belt. The fact that you hear the glow plug relay clicking makes me think it’s being “told” to turn on. I’d look at the smaller “signal” wires that go to the glow plug relay to see if they’re chaffed or shorted to another wire. I’d have to look at the diagram for that year (know it’s different than my 87 6.2”. Hope this at least is a start.

Ben

 

[Subourbon]

That makes sense, about the ameprsge draw and what woukd be the cause of the slippage.

I should clarify and mention that yesterday when I attempted the start, the GPs cycled normally, and after that starter noise, I turned the key back off and back to on again and that's where the relay started "blinking" at me.
Back to the amperage draw you mentioned it even cut out the lift pump a couple of times.

I'll inspect the wiring around the relay.
I'm wondering if the blinking is an issue with the relay and the the GPs running while engine is running is controller related? Isn't the controller tied in to the thermostat (coolant temp sensor)

Appreciate the reply, gives me somewhere to start. Start with the easiest, lol inspection of wires!
Cheers

 

[Blue Ox]

'82 would have had the multi-pin controller screwed into a port in one of the heads. I have a few of tbose kicking around if you need one. The glowplug light on the dash is directly connected to the circuit, so if it's coming on the glowplugs are on. Like @ital83 said they put a pretty significant load on the electrical system.

It should have nada to do with the starter. But I'm wondering if you don't also have a tired battery or bad ground that may be causing a low voltage issue.

 

[Subourbon]

Tired battery could be an issue. Interestingly the voltage gauge is one of the few that work on the vehicle. And i do believe I have a multimeter kicking around somewhere. That's usually the extent of my electrical trouble shooting. Clean grounds and check battery with the meter.
You think it's the controller then? Which I guess when breaking down the way it works,
Key in, run energizes the relay, which then stays on for a pre determined time set by controller, draws battery juice. Then after time elapsed, all juice directed at starter...
So maybe the controller is faulty and asking the relay for more, which would explain the clunking on and off... and could explain why it turns the GPs on when engine is running.
Relay is just a switch really... while I was writing up my essay there I was sure it'd be relay related.
And tired battery is a possibility for sure as far as starter goes.... wouldn't that mess with GPs too though, since it's such a big draw? Because they do cycle once properly...but then again I never had the lift pump "fade" while GPs are cycling. Damn. Good brainstorm session here
But this is food for thought. Appreciate the feedback guys thank you

 

[MrMarty51]

I’m not sure if this has two batteries. Get the wehicle, or the batteries to a parts store and have them tested. If it is a two battery system and one tests bad, do not mess around replacing just one battery. That will come back and bite You. Be sure to seperate the batteries so only one at a time is being tested.
Leroy Diesel dot com has a tool for removing broke GPs. You can borrow or buy one.
There is a temperature probe that tells the GPs to turn on tje controller. On this old of a unit I know knot where that probe is. I think My 2000 year unit the probe is part of the controller. Fire that parts cannon and install a new GP controller. Save the old one for a spare if the new one dont fix it. Good working Spare parts for these engines is not a bad thing. I have a jockey box full of various spare components for the just in case something fails when I am on the road. Not all parts stores packs in every component for these engines so We must be our own suppliers.

 

[Subourbon]

Yes 2 batteries!

I got snow here so I haven't separated them yet. But right off the bat I got 11.5v 11.6v on 12v batteries. Already that's not great.

Yeah I'm gonna get 2 new ones. Way I see it replacing 1 of 2 batteries is like doing one of your forward brakes. Do both lol.
I found a Haynes manual for the 6.2s the 82 to 84 years seem to have an exposed pin and it's not uncommon for dirt and moisture to get in there and mess around with proper functioning of the GP controller. They even suggested in the .annual (should problems occur) take it all apart, clean it put back together and a dab of silicone rtv over the pin hole to prevent issues later on. Nice.
I think I'll just buy a new controller and relay, just in case.
And yes, definitely have to be our own part sources with these vehicles.
There's a guy not far from me thst has 2 squarebodies, one as a parts truck and one he's re-doing, sadly he said he can't really afford to let go of anything as he won't know if he needs it further down the line.

Cheers everyone for pitching In ideas and advice! Now I just gotta go n do it!

For any Canadian users out there, what do you use for online parts? I go to wrench money. Its where I got all my brake hardware. GP controller there is 230$ around 180 USD, for that little guy. The one of few electronic components on these engines, haha!
Usa I know you guys have rock auto, believe me, I had a nice shopping list put together. Then came the shipping costs. Sweet Jesus! Lol.
Anyways, thanks again everyone

 

[Craig Nedrow]

On the left rear of the head, you have a temp sensor. This sensor tells the GP to turn on if the temp is (I have read varied numbers) under 125 degrees F. The clicking is the GP controller, located on the right head in back. The one you have will be a three pin, and there is a GP relay. Since you here the clicking this tells me two things, both good. 1) The relay is good. 2) The controller is also good. The AC ( ACDelco 1AERK00087) glow plug pulls about 6 amps X 8 = 48 amps. Your alternator is making noise because of the amperage draw. So....the temperature sensor can be bypassed by making a jumper wire, and inserting that jumper into the wire that would connect to the temp sensor. This will not hurt anything in the system. I have an 1985 C20 6.2 that I am presently working on, and it is a learning curve, but Here is a great source of info in PDF form that you can download and print out what pertains to you:

https://matveynator.ru/f/9efda83135c6d53e16e47aab9a0122c4.pdf.

THE 6 .2 LITER
DIESEL ENGINE
This is a Genuine GM tech manual long, but it has everything that you need to know.
To conclude. Make the jumper, install, and see if this cheap fix stops your GP from cycling.

 

[Craig Nedrow]

Yes 2 batteries!

I got snow here so I haven't separated them yet. But right off the bat I got 11.5v 11.6v on 12v batteries. Already that's not great.

Yeah I'm gonna get 2 new ones. Way I see it replacing 1 of 2 batteries is like doing one of your forward brakes. Do both lol.
I found a Haynes manual for the 6.2s the 82 to 84 years seem to have an exposed pin and it's not uncommon for dirt and moisture to get in there and mess around with proper functioning of the GP controller. They even suggested in the .annual (should problems occur) take it all apart, clean it put back together and a dab of silicone rtv over the pin hole to prevent issues later on. Nice.
I think I'll just buy a new controller and relay, just in case.
And yes, definitely have to be our own part sources with these vehicles.
There's a guy not far from me thst has 2 squarebodies, one as a parts truck and one he's re-doing, sadly he said he can't really afford to let go of anything as he won't know if he needs it further down the line.

Cheers everyone for pitching In ideas and advice! Now I just gotta go n do it!

For any Canadian users out there, what do you use for online parts? I go to wrench money. Its where I got all my brake hardware. GP controller there is 230$ around 180 USD, for that little guy. The one of few electronic components on these engines, haha!
Usa I know you guys have rock auto, believe me, I had a nice shopping list put together. Then came the shipping costs. Sweet Jesus! Lol.
Anyways, thanks again everyone

Put on a good battery charger, check the water level first if that is the kind you have, and charge those batteries 100%. I DO NOT THINK IT IS THE RELAY, OR CONTROLLER. Why? Cause is is working, also they are not dirt cheap. Just got one off amazon, (four pin) for about 80 bucks, made in America. The controller can be taken apart, remove from vehicle, remove two screws, there will be a silver plate and coil under, a copper contractor that rides on two pins. There are ohm tests to test this.

 

[Blue Ox]

If it's an original '82 he's going to have the earlier style controller/sensor with the divorced relay.

I have a couple of these kicking around if you need one.

You must be registered for see images attach

 

[Craig Nedrow]

that is correct, what I said in post 8. Changed in 1985

 

[Subourbon]

That's the one I got from the website entering the year, make n model etc....
The controller "works" yes, but not well, so it could be related to the temperature sensor? I always thought the GPs cycle as part of the ignition process. Then again, if I stop and get fuel, and start it up. There is no GP cycle. So yeah woukd make sense the temperature sensor comes into play.
Down the rabbit hole we go.
I found a video woth where the GP controller is. Buddy was saying you have to drop a bit of coolant from the radiator or have a coolant shower lol.
Yes the controller looks like what @Blue Ox has in his post.
Appreciate the help man, butni wanna see if I can even get to this thing first. And find the root cause of it.

Too many men on the field, relay, controller, sensor.
I'll have to pick up a charger and top up the batteries.
No no fluid on the batteries. They look new-ish. Motomaster I believe. There's a battery shop nearby. I'll pop em out of the truck and run them to the store and see what they can do

 

[Subourbon]

@Craig Nedrow

Cheers man, downloaded. Gonna read that and see what they say.
Hopefully that works and I only need to replace the temperature sensor instead of parts that may still be good!

 

[Blue Ox]

Glow plugs are only for cold starting, so they should not come on when the engine is warm. You'd need a schematic to see if there is a separate cutoff switch like the later systems. I don't believe there is. I always thought these had it built in to the controller, but I have an '85 as well, so can't refer to mine.

 

[Subourbon]

Bit of an update.
Batteries were toast. Got new ones, starting problem is resolved.
However the glow plugs still "blink" on and off. However, seems to be less fast.
Key on, lift pump and GPs on (10 or so seconds, then off) then blinking starts like insaid, seems to be less fast.
This was the case during both start ups.
One with the temperature sensor plugged in. The other start was with the temperature sensor un plugged
Does that rule out the temperature sensor? In the mean time, I'll clean the grounds and see if that makes a difference. Because the "blinking" is definitely happening less fast, and the only thing i changed were the batteries.
Thank you for all the input everyone!