Electrical system charging delayed starting issues m998 hummwv

I'm a rookie. Only have very limited knowledge on diagnosing and repairing automotive issues. Good at researching.

Acquired a '87 M998 HUMMWV upgraded in '07 about three months ago. Has 6.5 L & 60 AMP alternator. Over that time, voltmeter seemed to be in the green maintaining charge. Always fired up immediately without turning over at all, when just tapping the toggle switch to START. Never any smoke.
While running through a major rain storm, water began dripping on my left foot. Then panel lights went out one at a time. The next day found leak and repaired it (Under the hood found a grommet with two wires going through it had pulled out of the deck that the wiper washer reservoir sits on) and replaced panel lights - The replacement lights worked. Also found a wire hanging down (unable to determine what the wire goes to) below light switch panel and the wires that connect to it, that had gotten wet from leak. Took connection apart of the wire that felt wet and then left apart after drying it out. Later in day I accidently started it not remembering to reconnect that wire. Uncharacteristically, It suddenly took about 10-15 turns to start. When it did fire up, a plume of white smoke came out of tail pipe.

Since then, it now typically turns over 4-5 times or more to fire up with some smoke, when before it would instantly fire up smokelessly before all this happened. If i'm not mistaken, the glow plug light now only briefly flashes on. Before it would stay one for about 10 seconds before starting it, especially for the first time during the day.

Several weeks later while coming back from a trip, I notice that the voltmeter was on the edge of the red/yellow level. Not sure if panel lights blowing, leaving wire apart, delayed starting and inability to keep batteries charged are all related with a common cause.

Have attached the response of a mechanic who attempted to evaluate and repair each problem.
"I have tested different components of the starting and charging system on the HUMVEE numerous times and the Alternator has been charging +/- 28V every time. I have noticed once that the full 28V were NOT reaching the batteries only had 24V that one time. The Voltage gauge on the dash has been in the green consistently. Started it up this morning and it was a delay start and smoke did come out of the tailpipe like customer described. After visiting all the links customer has sent, I think it would be best to start with replacing the ground cables, PCB box, and glow plugs. These seem to be the most common components to fail and since the Alternator has tested good each time I do not feel it is needed at this time. Customer has stated he would like to eventually upgrade the Alternator, so if he would like to upgrade at this time we can or if he decides to hold off I don't see it being an issue. I would prefer the customer to supply the parts since he has known good resources. "

Had planned on adding a number of components/accessories (fans, GPS, stereo, back up camera, ext & interior lighting) in the near future until this all happened. Don't want to add anything until I get the electrical charging system and starting issues resolved.

New PCBox, new plugs, put on a grounding harness from block to starter, alt, body and electronic starter (ESS) box ( same thing as PCBox isn't it ?) All three ?


Any other suggestions ? IE Higher output Alternator to handle new components/accessories I plan to add. Any other preventative measures or upgrades to bolster electrical system.

Best place to get replacement parts ?

Appreciate any and all feedback !

It sounds like a wiring issue contributed to PCB box failure. Some folks on here have been able to repair their box, if the fault was visually obvious. I agree your alternator (generator likely) is probably OK.

Glow plugs are worth replacing if you do not know how old they are, as the older models have a tendency to swell and fail over time.

Agree to wait on adding accessories (and note that many you list are 12V accessories, and HMMWV's are 24V so you'll want a 24-12 converter to do it right, rather than tap a single battery since they don't like that).

Grounding harness is always a good idea.

ESS/PCB, same same. IF you decide to replace yours; #1 be sure to get the right one for your model engine and trans, #2 be certain the batteries are disconnected before wiring it in and be sure they are fully charged before reconnecting.

Always a good idea to disconnect the batteries before touching any wiring. Also, installing a battery disconnect is useful for this and as a theft prevention tactic.

Welcome to the site. There are plenty of tech manuals here if you haven't seen them yet: https://www.steelsoldiers.com/showthread.php?78861-TM-s-for-the-M998-series

Bulldogger

Have you checked and cleaned your grounds and / or installed a supplemental grounding harness. These truck have serious grounding issues. There are about 1 Billion threads on this.

There is a high probability your charging issue is ground related.

Your starting issue is most Likely sign of bad glow plugs and / or bad glow plug control box. This could also have been caused by a bad ground.

Pull your glow plugs and test them and see if they are burned up. There are plenty of you tub videos to help with this.



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Charging of the batteries runs through the EESS/PCB on 60 amp generator trucks.
your box is most likely toast...as well as your glow pligs

Time for a 200 amp upgrade with those mods in the future... that and new eess, coolant sensor and gp's... expensive fail, but hey welcome to the hobby.

I have only needed to do a eess, coolant sensor, gp's, and fluids in the three years of ownership with my hmmwv... so they break and it's a common failure...

papakb said:

I'm not sure why the trend seems to be to go to the 200 amp alternator in trucks running basic electrical loads. The upgrade is expensive. The installation kits are reasonable but the alternators are pricey and unless you want to run some high power radios or extreme electrical loads the 60 amp units are enough for a basic truck. The 60 amp alternators are readily available as are repair parts for them. Yes, there is an advantage to having the 12 volt tap but there are much simpler (and cheaper) ways to get 12 volts that a $500 alternator!

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Can’t agree more. 60 amps at 24 volts is the same as 120 amps at 12 volts. That’s about what standard half ton trucks have with all the heated seats and other electronics humvees don’t have. Even turning on all the stock electrical (lights, heater, wipers) can’t be more than a third of that at most. I have had my 40 amp battery balancer for going on 2 years now powering a stereo, winch, egt gauge and soon to be reverse lights. Granted some of these are intermittent loads, but I always have the radio cranked with an amp which is 15-20 amps at 12v. The balancer is also nice as I can hook up one 12 charger and charge both batteries at once.


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200amp is more reliable, easier to remove...and if a regulator fails, it’s 4 screws and your done in less then 5mins.
the 200amp is the standard generator for all HMMWV’s, the 60amp is out of the system.

Carrera911 said:

Can’t agree more. 60 amps at 24 volts is the same as 120 amps at 12 volts. That’s about what standard half ton trucks have with all the heated seats and other electronics humvees don’t have. Even turning on all the stock electrical (lights, heater, wipers) can’t be more than a third of that at most. I have had my 40 amp battery balancer for going on 2 years now powering a stereo, winch, egt gauge and soon to be reverse lights. Granted some of these are intermittent loads, but I always have the radio cranked with an amp which is 15-20 amps at 12v. The balancer is also nice as I can hook up one 12 charger and charge both batteries at once.


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best to go off watt, or Kw for power needs. 24v at 60 amp is only 1440 watts. 24v at 200 amp is 4800 watt.
half tons usually have 160ish amps at 12v, and 3/4 ton is 185 amp @ 12 volt. my 18' ram has two of the 185 amp 12 volt alternators, which is less power then the 200 amp 24volt alternator in my m1038. hah

anyways you want to look at it like a generator. standby v. prime power. take into account of surge, and overworking the 60 amp causing it burn up while causing more load on the engine. in this application Susie at the px barbershop is right; Bigger is better. especially since you do not have to factor in wet stacking...