LMTV ECU Voltage Regulator location?

[Dexis]

So I went out and disconnected all the batteries again and swapped in the voltage regulator off my reman alternator. Hooked everything back up and fired up the truck. Immediately the V gauge was almost rock solid around 28V.

Before the V gauge would bounce around between 24 and 28v wildly, until the huge spike under load at speed that tripped the trans codes.

I dont still have all 4 batteries connected and noticed while driving the truck back to the house that the V gauge was mostly around maybe 27.4-27.6V. So next step is definitely stepping down to 2 batteries to see if the alt can keep up then.

For now hopefully a pair of the 24’s will suffice. I’ll start working on getting a fresh pair of 27’s.

I still haven’t done any actual highway testing, and after all this I'm going to have a hard time trusting it until its got many MANY uninterrupted miles under its belt, but this looks the most promising so far.

 

[Ronmar]

The dual volt alt must have a proper connection to 12v in the middle of the 24v battery, with decent battery condition to regulate properly. It is not just a regulator it is also a balancer. If it does not see proper battery connection/response, this it will derate…
your loose connection at the alt could have also damaged the reg. Hopefully the spikes didn’t damage anything else…

 

[Dexis]

Went out for highway testing and it still threw the code. Same one, 1323. ECU volt high.

Volt gauge seemed more stable overall, less volatile jumping around, but still jumping around constantly.

Looking at the gauge this trip I realized some of my earlier figures were a bit off. I was thinking the line at yellow/green was 24V, just realized its 26V.

So before it was bouncing between 26 and 28V at idle like crazy. Under load that would jump into the 30-32 range periodically.

After new volt regulator at idle it was fairly solid just under 28V. Maybe 27.4-.6. As i got underway it would bounce around but less wide of a sweep. Maybe 27-29v average with the occasional ~30V. Now the more I drove that range became lower and lower. By the time I got home it was probably 25.8-26.6v range.

Threw high voltage again when it got up to full temp and around 45mph, about 80% of the way through the round trip.

Managed to make it back, parked it and grabbed the volt meter. 14.4 and 28.5 at alternator, and that was charging 14.3 and 28.4 at the batteries.

I also swapped down to 2 batteries before the trip. I threw the other two onto a charger but they were both at 100% in minutes, at least those two seem to be fine anyways.

So I'm not sure why my Volt gauge reads 26V and dropping. I guess maybe the alternator is bad? At this point all I can think to do is swap over the reman alternator and give it another shot.

 

[Dexis]

So i’m pretty sure I got burned on this alternator. Now that I think back they told me it was a “take off”, i originally asked if the had NOS, and the reman, but foe this model they just had the take off. I would think they’d test it before selling it. Maybe im wrong but here’s whats happening…

Bat disconnected, old alt out, new in etc…easy. Fired up truck. Immediately volt gauge began slowly surging 28V then crash to 20v, climb back…on repeat. Im pretty sure I read about this is another alternator related post. The only item that changed here was the alt. Volt regulator was working normally on other alt. Now i have green on 28V indicator light and flashing red on 14V light.

Alt charging excelent on 28V side but 14V wandering from mid 10V range to 15V.

 

[Ronmar]

The alt and batt are a system. The alt will not work right if there are connection and battery issues, so you must insure those things are correct before you can call it a bad alt.

 

[Dexis]

The alt and batt are a system. The alt will not work right if there are connection and battery issues, so you must insure those things are correct before you can call it a bad alt.

Well the other alternator didn't have this issue. Battery’s in the truck tested 12.7 each after over an hour of rest. The two I pulled showed 100% after just a minute or two on a charger. And aside from being undersized the batteries are fairly new, dated August 24.

The other alternator seemed to be slightly undercharging on both circuts. This one 28V seemed right were it should be and the 14V side dropping out to 10V every 2 seconds. Voltage regulator indicator lights showed proper function on other alternator and on this one shows a constant fault on 14V, confirmed with volt meter at 14V alternator post.

Ive gone through all the connections and everything is solid. Nothing is hooked up any different than the other alternator. If that one wasn't dropping in and out ever, forget 100% of the time like this new one I have a real hard time seeing how this alternator isn’t the issue.

 

[GeneralDisorder]

Welcome to 100A hell. Get a 200 or a 260.

 

[Dexis]

Does the 260 that is for the C7 engines work on the 3126?

 

[GeneralDisorder]

Does the 260 that is for the C7 engines work on the 3126?

The 260 is *THE* FMTV alternator now. It superceded the 100 and the 200 for all models. So the military has kits to install it on every single FMTV serial number back to 3116 trucks.

So yes. You can install the 260 on any FMTV with the right assortment of parts.

It's easier for serpentine trucks. The early C7 trucks are the easiest since the coil overs were designed to clear it already.

 

[Dexis]

The 260 is *THE* FMTV alternator now. It superceded the 100 and the 200 for all models. So the military has kits to install it on every single FMTV serial number back to 3116 trucks.

So yes. You can install the 260 on any FMTV with the right assortment of parts.

It's easier for serpentine trucks. The early C7 trucks are the easiest since the coil overs were designed to clear it already.

Any details or maybe just link(s) to swap procedure, parts, mods etc?

Ive seen a video of a 200A Humvee alt install with some basic modification. Only to read later in a post about needing to do something with the polarity protection as its only rated for 100A. And that was not done in the video I saw.

Long story short Id want to make sure I have the entire process and proper parts all lined out because Id assume slamming 2.6X amperage out into the systems incorrectly could have some devastating consequences.

 

[Ronmar]

The PPD isn’t an issue as the only current that goes thru it, is the current consumed by the truck via the dash power panel and that only changes if you add load… the PPD does serve as a tie point between alternator and batteries, but the 14 and 28 volt leads from alt and batteries are simply landed on the same studs on the ppd… if you keep those size batts, the batteries will never pull 260 anyway… Even the original size 6T batts in AGM are only ever going to pull 120A worst case…

the other option is to put in a 110A straight 24v alt(delco-remy, 350-450$) and use a 24-12 converter(170$) to power the truck 12v loads. Less expensive than any 260 you are going to lay hands on and very common/parts readily available. Any auto electric shop will probably have parts on the shelf for it… it can be fitted to the existing mount with some slight alteration…

 

[that_one_alternator_guy]

I have a freshly remanufactured and tested 260 AMP. And I wouldn't mind a core 100 AMP so if you're interested let me know. 7866143640