WAIT light - Only quick flash - Where to start?

[JO-0321]

Howdy...

When I turn ignition to run, the WAIT light flashes once only. Doesn't stay lit at all, it's just a VERY brief flash. It starts every time, but the first time I start it, it's a little slower to fire. Where should I start on that? Glow plugs? PCB? Something else?

I'm a novice mechanic, specially when it comes to electrical stuff...learning as I go...so if you use acronyms (ex. TSU - Temp sending unit), please let me know what you the acronym is!

Also, will mention weather is warm here. Maybe glow plugs just not needed due to outside temps?

 

[GuntherRommel]

Glow plugs or the start box is going bad, we have a spare if you need one. text me, Cheers

 

[MarkM]

Could possibly be a bad temp sensor in the block falsely indicating the engine is at operating temperature. As others have stated it could be the magic box or some bad glow plugs. I would start with an ohms test of the plugs. You do not have to remove them to test them. Welcome to the world of the HMMWV problematic glow plug system.

Mark

 

[JO-0321]

Alright...I've been reading about this all afternoon. I think I've got a good grasp on all of it. The only thing I'm still fuzzy on is the GPC vs. TSU. I understand the difference, but unsure of locations. Are they interchangeable and located in the same place? Thanks!

 

[juanprado]

Depends on what controller box you have.
Does it have 2 ports and color of label?
Or 3 ports?

 

[JO-0321]

Depends on what controller box you have.
Does it have 2 ports and color of label?
Or 3 ports?

I don’t know which box I have. I’m at work today through Monday morning so I’ll take a look then.
I’ll be able to figure out exactly what I have when I get home to look at it…I’m just running on pure curiosity now about the TSU vs GPC and if they’re in the same spot…but obviously serve different purposes depending on the control box.

 

[Milcommoguy]

Hello,

Short answer to the GPC - TSU. These parts screw into the water crossover, right side. It is the big bullet part with connector and 5 wires. In the beginning the GPC was the term of the sensor.

Basically it was a thermostatic electric switch that determined engine temperature. The signal was sent to the "BOX" up in the drivers foot well. There, simple transistor / integrated circuit logic timed and solenoids applied power to energize the glow plugs. GPC was the term used throughout all of the training manuals, drawings and it sorta stuck. That was 40 years ago more or less.

"TSU" came along when the automotive electrical world decided to design controls with micro-computers in vehicles. TSU with "chips" in it, worked with those matching BOXES, the computer, supporting input/output circuitry. Say the word computer and out pops the programmers. Proprietary software ran the starting and glowing. Between the various manufacturer designing it seemed to be no standard IMO. Has a computer ??? got to have a port. (anyone ever plug in?) so add and extra connector.

While on the surface the "BOXES & TSU" all look the same on the outside. Mix and matching can raised problems. Internal working was to a large point NO USABLE SERVICEABLE goodies inside.

"Just R&R. Military talk for toss it. Remove and replace as needed the military way" I get that, who as time to mess with a computer in a war machine.

During the hay day of HMMWV's with a couple of BOX suppliers... sometime call "SMART" with the confusion above, the sale of hundreds if not thousands to this day, with government contracts, law suites and big money was the game. (remember $400 dollars hammers) Somewhere there is a matrix as to what works with what.....

Jump ahead to the surplus market and being hobbyist, the learning curve was restarted (pun) most of the time. That's the IMO & what I've read short story.

I wonder who had the Glow Plug contract, CAMO

A peek inside>>>>


2 toasted FET glow plug output. ************ burned, welded control relay, check the affected heat signature on the armature. unit has 5 of then from you guessed it


micro-computer guess how many parts are in that



Worst case haha case prestolite GPC unit old school real old Yes, it was hanging in a truck. customer states " it ran good during the parade"

 

[98G]

I've seen weak batteries cause this.

 

[Mogman]

Alright...I've been reading about this all afternoon. I think I've got a good grasp on all of it. The only thing I'm still fuzzy on is the GPC vs. TSU. I understand the difference, but unsure of locations. Are they interchangeable and located in the same place? Thanks!

There is a sticky near the top of this forum that will tell you what TSU goes with your PCB/EESS box.
As suggested you can ohm out the glow plugs.
Are all the other electrical devices working OK?
Have you inspected/re-seated the PCB box connectors (inside and out)?
Cleaning all the grounding points is also a good idea especially the ones on the back of the engine and behind the inst panel and the front of the firewall (same bolt as the inst. panel)
The batteries should be fresh and charged
And of course always disconnect the batteries when doing any electrical work.

 

[JO-0321]

Thanks all…I feel like I’ve got a solid understanding of all this now. Determined I have the yellow label Nartron EESS. Still not confident it’s cooked, but probably likely. I’m testing glow plugs today…will replace if needed…and cleaning all grounding points. Will top off batteries with charger over night…then will see if glow plugs fire first thing tomorrow morning while it’s still cool…it’s been hotter than the 4th level of hell here the past few days since I’ve been fiddling with this so want to be sure that’s not been the reason . If not…decision time: Camotek manual glow plug control or the S3 box.

I’ll give one more update on all I find on my rig and the decision I make between Camotek and S3 (if needed)…and one more update after installing the new system (whatever I decide on). Hopefully someone will find all this helpful!

thanks again for all the help!

 

[mgFray]

If you do go down the path of glow plug replacement. Remember only buy from trusted sources, stay away from the ebay glow plugs. If the glow plug head is metric it is COUNTERFIT and will FAIL quickly! 3/8" hex, it's probably authentic.

You may also want to look at one of the detroit deisel glow plug remover tools. Helps a ton, as they tend to swell. But of course the tool doesn't work on couterfit glow plugs, for those you need a split-nut style puller. (OTC makes a good one for a reasonable price.)

(Can you tell I've already done through this?! What a pain.)

In my case, the glow plugs were shot. Replaced the glow plugs -- worked for a bit, then it got cold and didn't work. Found the TSU/Box wasn't supplying proper power.. replaced that.. worked great until it got to 20F.. Then found the temp sensor on the block (not the TSU, but the one in the back) went bad.. replaced that. Now it starts every time in first crank, even at 0F.

(My housemate, who was in the Army in the late 90's, said this HMMWV starts better then any they had driven while in the service... They kept telling me 20-30 second crank time was "normal", it's not.)

 

[JO-0321]

Glow plugs are bad. I tested 3 of them and they all failed. Tried to remove them to inspect them...all three are swollen and I couldn't get them out. I guess I'll be buying that ridiculously expensive black dog custom extractor tool. Hopefully new plugs will solve this problem.

 

[MarkM]

Hopefully they all come out with effort. Spray them all with a good penetrating oil and let them sit. On the new ones put some copper never seize on the threads before installation. Good luck.

Mark

 

[mgFray]

Glow plugs are bad. I tested 3 of them and they all failed. Tried to remove them to inspect them...all three are swollen and I couldn't get them out. I guess I'll be buying that ridiculously expensive black dog custom extractor tool. Hopefully new plugs will solve this problem.

I recommend the tool from Leroy Diesel.. looks like it's now about $65..

But with the counterfit plugs on mine, I ended up having to get the OTC one. Bought from amazon - "OTC 6005A Glow Plug Remover Tool Set".

 

[Mogman]

Glow plugs are bad. I tested 3 of them and they all failed. Tried to remove them to inspect them...all three are swollen and I couldn't get them out. I guess I'll be buying that ridiculously expensive black dog custom extractor tool. Hopefully new plugs will solve this problem.

Be very careful, first when replacing the glow plugs and again when testing the PCB box, it could have burned out the glow plugs to begin with.

 

[JO-0321]

Be very careful, first when replacing the glow plugs and again when testing the PCB box, it could have burned out the glow plugs to begin with.

Any recommendations on exactly what to look for while being careful after the new plugs are installed? Not sure how I'd know if the PCB box (mine's the yellow label Natron EESS) was the cause of the glow plugs burning out?? Or should I play it safe and just replace that box with an S3...or the manual glow plug system?

 

[Mogman]

The "box" can fail, even to the point where it activates the glow plugs as soon as the batteries are connected, rare but can happen.
So I would have a voltmeter or test light connected to one of the glow plugs, the wait light has nothing to do with what is actually happening at the glow plug.
So I would be ready to pull the battery cable if they stayed hot for more than 8-10 seconds.

I work on a box every now and then so I have a panel lamp in the dash of the Detroit which is where I test them, so I know what is actually going on at all times, I can watch the wait light time out, then I can watch the afterglow until it times out.

I recommend anyone not running a manual box have this dash lamp, but have never heard from anyone else that did it.

 

[JO-0321]

I work on a box every now and then so I have a panel lamp in the dash of the Detroit which is where I test them, so I know what is actually going on at all times, I can watch the wait light time out, then I can watch the afterglow until it times out.

Lost me on this one...sorry, electrical stuff is my biggest weakness.

 

[mgFray]

Where the electrical wire hooks to the glow plug. Pick one.. you want to have a meter ready to check the voltage on it when you first hook up the battery, when you first put it to run (wait to start) and after it starts..

It should be 0V (disconnected?) when the vehicle is off. Should be 20+V when the vehicle is first put to 'RUN'. When the wait to start light goes off, it might still have power, but soon after should turn off. After you start the truck, depending on outside temp, it MIGHT have power again (after glow).. but this should be for a limited time.

If the glow plug (in my experience) had power for more then 30 seconds, something is probably wrong. It needs to cycle on-off so it doesn't overheat.

 

[MarkM]

Where the electrical wire hooks to the glow plug. Pick one.. you want to have a meter ready to check the voltage on it when you first hook up the battery, when you first put it to run (wait to start) and after it starts..

It should be 0V (disconnected?) when the vehicle is off. Should be 20+V when the vehicle is first put to 'RUN'. When the wait to start light goes off, it might still have power, but soon after should turn off. After you start the truck, depending on outside temp, it MIGHT have power again (after glow).. but this should be for a limited time.

If the glow plug (in my experience) had power for more then 30 seconds, something is probably wrong. It needs to cycle on-off so it doesn't overheat.

I had to replace my glow plugs and after I installed the new ones I started the truck for maybe a minute and cooked my brand new glow plugs. Turns out the relay in the box had jammed on so it was sending 24v to the glow plugs when the ING switch was in run. I cursed a lot that day.

Mark