Glow plug sysem failure question

[llong66]

Hello all as the title says, I have had a failure in my GP system and have a question. Its a typical, beautiful fall day in Indiana cold and rainy. Lol. I went to start my truck for the first time today and no go. Cranked as usual, nice and fast, but I was getting nothing but some white smoke out the exhaust. I noticed that I was not hearing the normal clicking for the GP relay so I went to just jump it to ground as a temp meaure to get it fired up, still no click. Next I checked the voltage at the individual plugs, 24.7v! Needless to say they were all fried I just thank the CUCV gods that they had not swollen and they came right out.
My question is: Could a bad relay allow full system voltage to get to the GPs? Without doing further trouble shooting I cannot see what else it could be as I said even jumping the small terminal w the blue wire to ground, I get not activation of the relay, no "click"
I will, for sure be doing the resistor bypass as part of the fix to this problem. It kinda bites as the plugs I have have less than 3k on them.

Thanls much!
Greg

 

[quickfarms]

The circuit uses the resistance of the glow plugs to lower the voltage that each glow plug actually sees to 12 volts, nominal.

 

[llong66]

I know this, but as I said the relay does not appear to be functioning, the plugs are new 60Gs so I don't think it was a simple plug or two causing a cascade failure. It seems to have happened all at once.Now that I have them all out, 3 of them have "exploded" in the cylinders the tips are blowen off I am REALLY glad it didnt start! I just hope I can fish out the broken parts by removing the injectors rather than having to remove the heads.What I would like to know if a failed relay could cause this?

 

[MarcusOReallyus]

Next I checked the voltage at the individual plugs, 24.7v!

When are you measuring this? When the GP relay is engaged? There should be zero volts at the plugs if it is not engaged, or if it is not working at all.

My question is: Could a bad relay allow full system voltage to get to the GPs?

No. The only way for that to happen would be for the resister to short, or to jumper the resister, OR, if all of your GPs have burned out and are open.

Still, there should not be any voltage if the GP relay is not engaged.

It sounds to me like your GP relay stuck on and fried your GPs open.

Without doing further trouble shooting I cannot see what else it could be as I said even jumping the small terminal w the blue wire to ground, I get not activation of the relay, no "click"

That would be true if the the relay is stuck ON. That would account for voltage at the plugs when it should not be engaged.

I'd thorougly test that relay OFF the truck before you put in new GPs.

 

[scottladdy]

I'd thorougly test that relay OFF the truck before you put in new GPs.

Or just replace the relay. I have seen it reported (and experienced it once myself) that the old relay will not function well after the resistor bypass. A new relay seems to be the fix. Also, considering what $$ you will be putting into new AC60G's a new relay is a relatively small investment.

Hope this helps ...

 

[llong66]

Thanks for all your help and suggestions! I think I have traced the problem down to a faulty GP control card. When I removed the ground from the relay it clicked "open", no voltage to the GPs. When I ground the relay manually it functions fine. The 24 volts I was reading at the plugs was due to them all being fried! I have bypassed the resistor bank and am going to replace the relay when I get new GPs. I will go with a manual activation on the GPs until I can get a replacement card. Now I just have to hope I can fish out the pieces of GP that are left in the precomp chambers. I am going to remove the inj. from those cyl and get one of those HF inspection cameras and see if I am able to see if I need to remove the heads or if I am lucky, just fish the pieces out that way.
Wish me luck!!!

 

[rsh4364]

I thought 60Gs didn't swell..or explode.

 

[MarcusOReallyus]

I think any GP would misbehave if it had full power for waaaaay too long.

 

[Skinny]

I agree, a 12v GP being fed 24v will probably not like that too much. This is just another case where any new CUCV owner should either be checking for a resistor bypass or doing the mod themselves. Unless you are trying to stay 100% original and actually plan on jumpstarting your dead Cuck with the NATO slave, absolutely no reason to get stuck like this.

Sorry to hear about your damage. Pick up the pieces, do the mod, and your GP circuit will thank you.

 

[firefox]

If you plan on getting an M35 or some other mil truck, you might want to keep it original.
I have used my M1008 to jump start my M54 and my M211 more than once.

 

[MarcusOReallyus]

If you plan on getting an M35 or some other mil truck, you might want to keep it original.
I have used my M1008 to jump start my M54 and my M211 more than once.

And what percentage of CUCV owners have other 24v vehicles?

 

[cpf240]

If you plan on getting an M35 or some other mil truck, you might want to keep it original.
I have used my M1008 to jump start my M54 and my M211 more than once.

Just as a note... the above scenario would in no way be affected by the GP resistor bypass having been done in the M1008.

 

[Skinny]

Just as a note... the above scenario would in no way be affected by the GP resistor bypass having been done in the M1008.

Agreed

Only the lucky MV owners have the luxury of having a spare 24v vehicle to jumpstart a dead one! Worst case is just install 24v HMMWV glow plugs, bypass the card, and install a manual pushbutton if you are so worried about it. I would rather modify the system that way than risk running that 30 year old resistor.

 

[rsh4364]

I think any GP would misbehave if it had full power for waaaaay too long.

My bad,I forgot the gps were getting 24volts.I did the resistor bypass,new solenoid and new 60gs recently,starts great now.But only been down to 30 so far this year.

 

[firefox]

If you switched to the 24 volt GP's, and removed the resistor, why would you need to
bypass the glowplug card? The glowplug card just powers the GP relay with 12 volts
and the relay provides power to the glow plugs, right? Am I missing something here?

 

[doghead]

That will not work.

The glowplug card senses the voltage and looks for the drop to 12V. Without that, it would not work correctly.

 

[llong66]

Hello all! Got er done! Set of new AC60G glow plugs and a new relay, the relay is from Advanced Auto manufactured by BWD, part of their Z series, part no. GPR1Z, and its made in the USA!!
The relay was only $20. It matches exactly what was already on the truck. The one I had still functions, but since I did the resistor bypass I went ahead and replaced it.
I am not sure if it is the cause of everything or not, but my controller card has the zenier diode I have seen burn out on alot of other members cards burnt out.
I had initially been running the truck with out the temp switch in the rear of the drivers side head while locating a new one. So, I am unsure if this caused the glow plugs to run more than they should have, leading to failure of one or two causing a cascade failure, ultimately causing my problem, or if the malfunction of the card caused the problem, but either way all is well and I just have to get a new card. I am going to get one from Antennaclimber here on the board. I am just using a push button for now.
Thank you all for your help and suggestions through this!

 

[firefox]

I am thinking about putting a single pole double throw switch feeding the glow plug relay.
one source is via the resistor and the other source via the 12 volt bus. This way I would normaly
be in resistor bypass mode, but if I needed to jump my M1008 from one of my other trucks, I could just switch back to the resistor feed.
Does anyone see a problem with this approach?

 

[MarcusOReallyus]

Just the cost of the switch. It will need to carry about 100 amps, plus a safety margin, so call it a 120 amp switch.

 

[doghead]

Unless your front battery is dead or damaged beyond taking a charge, you do not need to worry about it.

When do you need to start it with a battery that is damaged or dead(and will not take a charge)?

The original design meets battle ready/use conditions. In the civilian world, this does not exist.