Glow plugs burning out, even with manual controller

[Farnorth]

I have a 1988 M998, on which I installed a ford style relay and push button manual controller. Has been working great but recently wouldn’t start. Turns out all glow plugs were non-functional with a resistance test. I installed a new set of 24V plugs from Kascar, they worked excellent for a while and now appear to be burned out as well. The relay is not sticking on which was my first concern. I’m holding the button for about 8 to 10 seconds before attempting to start and other than that I don’t know what could be the issue.

 

[Action]

Could the issue have been heating the plugs when not needed? Do your plugs have spade terminals or plugs on the ends?

Why didn't you fix what the problem was in the first place?

 

[86humv]

Did you make a harness, or splice into engine harness ?

 

[Milcommoguy]

I have a manual, custom built glow plug controller and 8 to 10 "real" seconds is tooo looonnngg with a good set of batteries. For mind from a first time, cold start, count... ON 1,2,3 OFF 1,2,3 ON 1,2,3 and start. Below 40 degrees add another count cycle as needed. Never a problem, no rough and puff smoke, no EMP, CPU, voodoo magic to fail, no high dollar control box and built in theft protection.

MAKE sure contractor can handle 150 amps continuous resistive current. It's a bit over kill on rating and to not use junk imported contractor. Watch voltmeter dip for the 90 amp +/- pull down on battery voltage to verify operation.

Manual or Smart systems, to long makes for short glow plug life. HI, GREG.............

CAM

 

[papakb]

When the LAU control boxes were being issued they had a separate cable that connected the control box to the glow plugs. The boxes themselves were crap but the cable that came with them could be used to make a totally independent glow plug system that would be an excellent option for a manual control system like these that would eliminate any chance of power getting backfed into one of the newer control boxes. They sometimes appear on ebay for cheap dollars. Just a thought.

 

[tage]

How do you know the relay isn't working right?

 

[Milcommoguy]

The later PCB's having the 2 plugs (and not counting any diagnostic plug) have only one #8 ga wire to the glow plugs. It is pin "D" of the engine harness. All 8 plugs are spliced together in the harness to this wire. Removed (cut free and use this for feeding plugs) from controller and there is no chance of back-feeding any voltages to anything. If your at this point DON'T CUT ANYTHING. It is a couple more steps to toss the whole concept, BUT keep the metal box as it can be reused to build your direct replacement manual control box in.

Other circuits supported by the PCB to make the "not so smart box" must also be considered such as: run & cold start power, start & starter lockout, transmission neutral safety, accessories power feed and the famous wait light. At the same time you can ditch the controller in the water crossover.

For such a simple engine, dumb is better, Whoever dreamed up the idea to add a computer to it was thinking MONEY MAKER on the replacements sales, IMO.

On other note for the radio guys. If your running HF gear, there is a good chance that (RFI) creating uncontrolled failure / operation. Been there, seen that, not pretty.


CAMO

 

[Retiredwarhorses]

The later PCB's having the 2 plugs (and not counting any diagnostic plug) have only one #8 ga wire to the glow plugs. It is pin "D" of the engine harness. All 8 plugs are spliced together in the harness to this wire. Removed (cut free and use this for feeding plugs) from controller and there is no chance of back-feeding any voltages to anything. If your at this point DON'T CUT ANYTHING. It is a couple more steps to toss the whole concept, BUT keep the metal box as it can be reused to build your direct replacement manual control box in.

Other circuits supported by the PCB to make the "not so smart box" must also be considered such as: run & cold start power, start & starter lockout, transmission neutral safety, accessories power feed and the famous wait light. At the same time you can ditch the controller in the water crossover.

For such a simple engine, dumb is better, Whoever dreamed up the idea to add a computer to it was thinking MONEY MAKER on the replacements sales, IMO.

On other note for the radio guys. If your running HF gear, there is a good chance that (RFI) creating uncontrolled failure / operation. Been there, seen that, not pretty.


CAMO

Not sure if your aware...but the M939 series trucks use a PCB as well, this is not a new concept.
the PCB/EESS has several other functions other then Cycling glow plugs.
having had hmmwvs since 1999, I’ve not had the issues that would ever make me go to a manual GP toggle switch...your truck, do want you want, but at my shop, we fix so it works like the other 1/2 million hmmwvs.

 

[Milcommoguy]

That's right RWH. Being in the business your in, you have to keep to a standard. And I understand that there are the purest to keep it factory. I like factory. I like beer too. Not tying to hijack anyone's fun or sales to enjoy the hobby.

When mine took a dump I wasn't in the know or had sourced a replacement. (like many here)

Knowing what it takes to start a bare bones 6.2L (and owning may 6.2L CUCV's) this was a local challenge to do what I know and get it running. Learned that the BOX was overly complex, but needed for today's push-button, on the go solders and still the wait light means WAIT or does it?

The Hmmwv and all the others just a hobby. For me it was the challenge and it works. I understand it completely, no pricey parts, simple. It plugs right in, a direct manual, form and function replacement. No computer with a thousand points of failure. Can't wait for it sitting on the "OUT OF SERVICE LINE" for a 600 dollar box and another 100 buck for plugs. Now I did have to train the wife on how to start it. Simple, but I think she forgot ... a good thing. LOL

Didn't know the M939 had a PCB. Not surprising with the trend to computerize everything. Guess if you got it use it (computers chips) then design it in. Add it on the the price tag.

Now my 2018 Toyota Tacoma as a $h$t load of sensors, computers, bell and whistles. It's "fly by wire" push button start, computer to shift gears, computer to get out of ditch, etc. Because it won't start, mechanic stated it could be an $1800 module. Five computers working together to go down the road. I got the 8 year total bumper to bumper, no out of pocket warranty for that day when I push the button and nothing happens. I really wanted an old key in hand and to hear the click.

So the day the Toyota doesn't start... guess which truck I am taking on the beer run? I like BEER.

Do YOU LIKE BEER? RWH

Alexa, do you like beer?

CAMO

 

[Retiredwarhorses]

That's right RWH. Being in the business your in, you have to keep to a standard. And I understand that there are the purest to keep it factory. I like factory. I like beer too. Not tying to hijack anyone's fun or sales to enjoy the hobby.

When mine took a dump I wasn't in the know or had sourced a replacement. (like many here)

Knowing what it takes to start a bare bones 6.2L (and owning may 6.2L CUCV's) this was a local challenge to do what I know and get it running. Learned that the BOX was overly complex, but needed for today's push-button, on the go solders and still the wait light means WAIT or does it?

The Hmmwv and all the others just a hobby. For me it was the challenge and it works. I understand it completely, no pricey parts, simple. It plugs right in, a direct manual, form and function replacement. No computer with a thousand points of failure. Can't wait for it sitting on the "OUT OF SERVICE LINE" for a 600 dollar box and another 100 buck for plugs. Now I did have to train the wife on how to start it. Simple, but I think she forgot ... a good thing. LOL

Didn't know the M939 had a PCB. Not surprising with the trend to computerize everything. Guess if you got it use it (computers chips) then design it in. Add it on the the price tag.

Now my 2018 Toyota Tacoma as a $h$t load of sensors, computers, bell and whistles. It's "fly by wire" push button start, computer to shift gears, computer to get out of ditch, etc. Because it won't start, mechanic stated it could be an $1800 module. Five computers working together to go down the road. I got the 8 year total bumper to bumper, no out of pocket warranty for that day when I push the button and nothing happens. I really wanted an old key in hand and to hear the click.

So the day the Toyota doesn't start... guess which truck I am taking on the beer run? I like BEER.

Do YOU LIKE BEER? RWH

Alexa, do you like beer?

CAMO

I don’t know about a trend....m939 and hmmwvs are early 1980’s designed vehicles...it’s a simple box with electro mechanical relays in it.

Beer is my preferred beverage

 

[Milcommoguy]

Well, that's good we agree on BEER. You are right again on the old truck designs too. The trend has been coming at us for at least that long. That would be true of the those that roiled down the line in the 80's. First without seat belts and ungraded to two point then three point belts, maybe even four points ??... I don't know.

Would be true of the control boxes. Simple relays, thermal timer, matched senders, basic electric stuff most of us could figure out.

Somewhere along the way, lets add some transistors and diodes in there and one of those PICs. Engineers love this stuff. Marketing could make a bundle. We won't tell you or show you how it works, but you will love it. If bad just swap it out. Did they ever rebuild them at depot level ??

> http://ww1.microchip.com/downloads/en/DeviceDoc/39977c.pdf < Data sheet. Reads like a TM.

Late box open


Brains up real close. See the link to this puppy.


Start relay


Master power contactor


Glow plug pwr Hex FET's


That little 1/2 square of plastic (see picture two) with some sand, maybe smoke too, inside along with all the other stuff to cycles the whole "todo" to get the engine to "vroom". Not apposed to technology. TV remote control GOOD, Cell Phone OK, Pacemaker REAL GOOD, Old hmmwv NAY. Just to much stuff going on for glow plugs and holding the injection pump solenoid in.

More time and money to buy and drink beer. So that's how it goes here at Camp CAMO. Take care and keep them rolling RWH.

 

[Action]

The boxes were not expensive until GP started selling all those HMMWVs.
And for anyone that cares, not all PCBs are Smart Start boxes. I think that term is starting to get used quite loosely.

 

[tage]

Supply and demand... Some people have gotten rich off this niche market...

 

[ikoinu]

I have a 1988 M998, on which I installed a ford style relay and push button manual controller. Has been working great but recently wouldn’t start. Turns out all glow plugs were non-functional with a resistance test. I installed a new set of 24V plugs from Kascar, they worked excellent for a while and now appear to be burned out as well. The relay is not sticking on which was my first concern. I’m holding the button for about 8 to 10 seconds before attempting to start and other than that I don’t know what could be the issue.

Just wanted to give you some of my own experiences.

So I built a manual glow plug controller, running a secondary HMMWV glow plug harness due to my plugs getting fried. The box was putting 24v constant through the factory harness killing the plugs, otherwise the box was working fine with 8 second wait light.

The setup used a momentary button, but I recently found that I had burned my new plugs out after 3/4 of a year. The reason for this was holding the button 8-10 seconds each. It was too much for the little suckers (Kascar Hmmwv 24v).

Swapped the plugs and all is well again. If everything else is good with your system, I'd suggest trying less time on the button (obviously in cold climates ymmv).

I agree that the manual controller is the way to go instead of $600 box swapping all the time. One box to rule them all might also be a good thing, just haven't seen it yet.

Best,
Steven

 

[Milcommoguy]

It seems there as been a bit of a increase in pricing from the 90's and maybe a little failure rate ? > http://www.dtic.mil/dtic/tr/fulltext/u2/a393867.pdf <

Inflation has hit the hobby? Just when your having fun, shell out more money.

And for the those looking to go Hmmwv. A simple, informative read. > http://www.militarytrader.com/military-vehicles/hmmwvs-in-the-hobby-part-ii-buying-tips <

I like beer, Hmmwv OK too.

CAMO

 

[tage]

Just wanted to give you some of my own experiences.

So I built a manual glow plug controller, running a secondary HMMWV glow plug harness due to my plugs getting fried. The box was putting 24v constant through the factory harness killing the plugs, otherwise the box was working fine with 8 second wait light.

The setup used a momentary button, but I recently found that I had burned my new plugs out after 3/4 of a year. The reason for this was holding the button 8-10 seconds each. It was too much for the little suckers (Kascar Hmmwv 24v).

Swapped the plugs and all is well again. If everything else is good with your system, I'd suggest trying less time on the button (obviously in cold climates ymmv).

I agree that the manual controller is the way to go instead of $600 box swapping all the time. One box to rule them all might also be a good thing, just haven't seen it yet.

Best,
Steven

How was your coolant temp sensor?

 

[ikoinu]

Not sure, but when I bought it from a guy I knew who had not had it very long from auction (he titled it here in CA, saved me a headache), he had purchased a new temp sensor so I dropped it in, no change.

I would consider myself to be one of those people that want to keep the vehicle as close as possible to the military's intended form. I do make concessions for comfort and reliability due to it being a dd, such as manual glow plugs, block heater, seat heater (still looks stock!), 200 amp generator (put in yesterday due to crappy cast 60 amp bracket breaking at the power steering pump), factory hydraulic winch, etc.

 

[tage]

When my box would keep the glow plugs on. I pulled the coolant sensor and the chip was black and burnt. I suspect that was the cause, I had a new box on hand so I just replaced everything.

 

[sue]

I thought that the glow plugs only got 12volts,
At 24 volts they don’t last long.

 

[86humv]

I thought that the glow plugs only got 12volts,
At 24 volts they don’t last long.

Cucv's are 12 v