M998 Electrical Issue

[lynchmob15]

I have been searching through the threads however couldn't find anything to help me troubleshoot my issue. Since I got my truck every time it starts the generator gauge would bounce around inside the green zone for anywhere between 1-4 minutes then it would stabilize in the green.

Thursday I went to start the truck and the batteries had the power to slowly turn the engine over but it wouldn't fire. I went ahead and charged the batteries for a bit and started it with not issues. On Friday I started it to move it and noticed the generator gauge bouncing around unfortunately it was in the yellow zone and then stabilized and stayed in the yellow. I put my meter on the negative of one battery and the positive of the other and was seeing 12.5 volts with it running.

I am trying to determine where my issue is. I was figuring it could be: the batteries, the generator or the voltage regulator. Can anyone give me advice on how to isolate the issue? I did see some posts recommending to check the voltage at the Charging Post but I don't know where that is so if someone could assist me in finding that I would appreciate it as well.

 

[Mogman]

Welcome to the forum!
The volt meter bouncing for a few minuets is called after glow, it is the EESS box pulsing the glow plugs on and off to keep them warm as the engine warms up a little and is perfectly normal,
You have to put the meter on the neg of the rear battery and the positive of the front, I suspect you will see about 25V which means it is not charging.
One hard lesson to learn is you should disconnect the batteries to charge them or you can fry the regulator.
I would disconnect the batteries and give both of them a full charge, re-connect the batteries (correctly) and try again.

 

[lynchmob15]

Thank you for the information it is very much appreciated. When the batteries were low I did disconnect all of the battery wires and charged them individually with a "fast" charge just to get it running. When i put the meter from the rear battery negative and front positive it was showing 12.5 which i found very odd. I will double check it again shortly and then fully charge both of the batteries and check again. Really appreciate it.

 

[Coug]

if you're reading 12.5 across both batteries, either they are hooked up incorrectly or you have failed batteries.
Did you check voltage on each battery individually?

 

[lynchmob15]

After more inspection I found the bolt under the generator actually broke and it is now moving around. Can anyone tell me what size bolt it is, the only thing I have is the head of the bolt so I am not sure the length or threads. Thanks in advance for the assistance

 

[springer1981]

After more inspection I found the bolt under the generator actually broke and it is now moving around. Can anyone tell me what size bolt it is, the only thing I have is the head of the bolt so I am not sure the length or threads. Thanks in advance for the assistance

That's what the TM's are for. Here's where you can find them. If you plan on keeping this truck, you are going to need to know how to use them. Seems like a good time to start. https://www.steelsoldiers.com/threads/tms-for-the-m998-series-hmmwv.78861/

 

[Mogman]

What size alternator do you have???
Here is the TM you need at this time but you need to know what alternator you have.

https://www.steelsoldiers.com/upload/M998/TM%209-2320-280-24P-1%20HMMWV%20Parts%20vol%201.pdf

 

[lynchmob15]

What size alternator do you have???
Here is the TM you need at this time but you need to know what alternator you have.

https://www.steelsoldiers.com/upload/M998/TM%209-2320-280-24P-1%20HMMWV%20Parts%20vol%201.pdf

Thank you for the assist. I will check out that TM. I am new to this forum so really appreciate everyones assistance. I owned the truck 4 years now and I am finally starting to have some issues that need to be addressed.

 

[Coug]

When asking for assistance like this starting off with the model of truck and what alternator is in it is extremely helpful for those who want to help.
As the saying goes "garbage in, garbage out" meaning if you don't give us good information we can't give you good advice.

"bolt under the generator" could mean multiple different bolts of different sizes in different locations, so without a better description of which bolt, or pictures of the spot it's broken off at all we can really do is ask you to use the parts manual, which can be a bit confusing to those unfamiliar with them (not to mention it's pretty big and covers multiple engine setups)


So now that that is out of the way, a couple years ago on my M1123 truck with 200 amp generator system, red dot aircon (doesn't matter for this particular issue, but does change some other parts in the serpentine system), and below serial number 196900 (early style serpentine setup), I had a loose generator mounting bracket. I did a thread about it at the link below. If yours has the same 200 amp setup and lower serial number it might be useful. If you have a different setup it might not be useful at all.

Sheared generator bracket bolts.

When I first got the truck(m1123, 200 amp generator) the stud on the exhaust that holds the rear generator bracket was sheared, and a couple of the front bolts were loose. It started making noise again, so I checked, and the exhaust stud is sheared again, and at least one of the front bracket...

www.steelsoldiers.com

 

[lynchmob15]

When asking for assistance like this starting off with the model of truck and what alternator is in it is extremely helpful for those who want to help.
As the saying goes "garbage in, garbage out" meaning if you don't give us good information we can't give you good advice.

"bolt under the generator" could mean multiple different bolts of different sizes in different locations, so without a better description of which bolt, or pictures of the spot it's broken off at all we can really do is ask you to use the parts manual, which can be a bit confusing to those unfamiliar with them (not to mention it's pretty big and covers multiple engine setups)


So now that that is out of the way, a couple years ago on my M1123 truck with 200 amp generator system, red dot aircon (doesn't matter for this particular issue, but does change some other parts in the serpentine system), and below serial number 196900 (early style serpentine setup), I had a loose generator mounting bracket. I did a thread about it at the link below. If yours has the same 200 amp setup and lower serial number it might be useful. If you have a different setup it might not be useful at all.

Sheared generator bracket bolts.

When I first got the truck(m1123, 200 amp generator) the stud on the exhaust that holds the rear generator bracket was sheared, and a couple of the front bolts were loose. It started making noise again, so I checked, and the exhaust stud is sheared again, and at least one of the front bracket...

www.steelsoldiers.com

From what I can tell it is a 200A S/N 196900 and below. Can you recommend a site that would carry these bolts.

being a newbie I truly appreciate everyone’s assistance

 

[Mogman]

Here are the two pertinent documents, they are relatively easy to look up in the TMs you have been directed to before.
IF the bolt you need does not have the actual dimensions listed you can google the NSN number then follow some of the hits and the dimensions will be listed.
As has been mentioned before you have not provided enough information to determine exactly what bolts you are talking about, there are many different bolts involved, you should be able to figure it out with the help provided.

 

[Mogman]

You should have listed the exact model truck also so you can confirm the Use On Code (UOC) is valid for your application.

 

[lynchmob15]

IT's a 1992 M998. 37-1 it is bolt #1 part # B1821BH044F975N.

 

[Mogman]

If you google the NSN number 5305014299149 or that number you listed you will see HPG and Kascar (real4wd) has those bolts.
it also gives the dimensions of 7/16-20 X 9.75" but that is a rather odd bolt so it would be easier to order it from a HMMWV dealer than finding it at the local bolt shop but anything is possible.

 

[Mogman]

Your UOC code is H13, BUT that is not the original alternator, or even engine for that matter so sometimes you have to interpolate what is in the TMs, in this case you should be good with the documents I have provided but you will notice H13 is not listed in the applicable UOC codes.

 

[Mogman]

Be very careful when you replace that bolt, make sure you have all the correct spacers in the correct places or you can snap off the mounting ears on the alternator and that gets very expensive..