LMTV ECU Voltage Regulator location?

[Dexis]

Hey all, I've got a new to me 2001 m1078a1 that started throwing the D1323 code, voltage from ECU high, on the Trans.

So im trying to locate the ECU voltage regulator, part # 19207-12378784-001

Ive read as much as I could f on here and tried to dig into the service manual but I just cant seem to figure out where this part is located in/on the truck.

Any help greatly appreciated as I am scrambling to try and have this up and running for our towns 4th of July parade!

 

[Ronmar]

There is no ECU voltage reg… the ECU and TCU use raw truck power. If it is throwing a high voltage code the alternator is outputting high voltage(bad alternator regulator?), or the electronic control unit has a fault. What are the truck voltages? should be within 1/2Volt of 14.1/28.2V at the alternator terminals…

 

[Dexis]

When I checked the alternator last week i was getting 13.8-13.9 and 27.8-28.0. I did just get a reman alternator with regulator. Time to swap those in?

 

[Ronmar]

those voltages sound OK(maybe a little low). also confirm all your connections between battery and alternator are clean and secure. intermittent connections to the main load(battery) could cause voltage spikes within the system...

 

[Dexis]

Everything was tight at the alternator/volt regulator and all 4 batteries when I checked, unless there is/are additional component(s) in between. I’ll go trace from the batteries back to alt to make sure. Past that I guess I'm going to swap this alternator and see if anything changes, unless theres something else I'm missing here.

 

[Ronmar]

The polarity protection device/LBCD on an A1 is located inboard of the spare tire. it is in between alt and batteries and its 4 connections connect 6 major cables to batts, alt and cab, for 14 and 28V respectively. if you have a manual disconnect switch and relay(box to the rear of the battery box), those devices are also in line between batt and LBCD.

 

[Dexis]

Awesome, thanks. No battery disconnect on mine but ill go drop the spare right now and go back down the line from alt to batteries before I start taking anything apart at the alternator.

 

[Dexis]

Nothing loose on the polarity protection device/LBCD or anywhere else along the line that I can find. Guess im headed to the alternator swap unless theres anything else I need to check first.

 

[Dexis]

Ok, interesting development. I was 2 bolts away from having the alternator out…had the long alt mounting bolt left holding it in place and the last connector on the alt I was about to remove was the 28V bolt.

My wrench just tapped it as I was trying to slide it into place and what do you know, it rolled an 1/8 of a turn out. That bolt was only hand tight. All I can think is I must have missed it my last pass through because the 14 and 28v cables being so close and tied together must have made it seem that the 28V lug was strapped down solid.

So I guess I owe it to myself…and this wildly expensive reman alternator…to put this all back together as is and go back out to test it one more time. Fortunately the tear down was super straight forward so worst case Im only out an hour of work if I have to backtrack.

 

[Dexis]

Well holy smokes, that didn't work out. Here’s the update step by step.

Put it back together and started heading off the property to the main road. On the way out I noticed the volt gauge seemed much less erratic. Before it was a near constant and fast bounce between 26 and just over 28v, (aside from the spikes that go off the charts that are my issue). On the way out this time it seemed much more solid floating between 26 and 27 for the most part. It has always gotten more erratic at higher speeds/engine load.

And once I pulled out onto the main road at 40mph that started happening again, seemingly not as severe as before but still erratic, at times jumping all the way up to just under 30v. And then it happened again, volt gauge pegged off the charts and Trans Light popped on again. I went ahead and rolled to a stop off the side of the road. Everything cleared as usual once i came to a complete stop.

Busted a U turn and started heading home. Made it back to my dirt road, did it again about half way down. Same deal, stop, everything resets, start driving again.

Now for the real news, about 300 yards from my front gate the volt gauge jumped off the charts AND STAYED THERE…Immediately the dash lights were flashing and spasming brighter, the radio started spitting out static, transmission was shuddering…I immediately rolled off to the side of the road and shut it down. I tried turning it on one more time to see if it would happen again and sure enough, voltage off the charts and everything is freaking out. Only had it on for maybe 2 seconds that time.

Well poop, grabbed my keys and walked home.

I have a theory that id like to run by you guys.

Im wondering if that 28V connection being loose-ish could have been straining or wearing out the voltage regulator. Maybe this issue was the voltage regulator dropping out intermittently or only under harder loads. This never happened driving around my property at 2-15mph. Started happening at highway speeds when truck was warmed up all the way. Maybe the voltage regulator finally let go completely?

Id assume bad alternator would be low to no voltage but bad regulator would get you voltage as high as the alternator could generate getting pumped through everything.

 

[Ronmar]

Your assumption sounds about right.

The reg is probably an issue. you should be able to disconnect the EXC wire from the reg to keep it offline and drive it home on battery power alone...

 

[Dexis]

I think ill try and swap my regulator for the one on the refurb alt I picked up. I also found this video about the “exciter wire replacement for high/low voltage” and wonder if this is something I should look into at the same time…

My truck already only has the E wire connected to the regulator. Also wondering if this too could have been the initial issue, potentially wearing on the regulator as well? Possibly grasping at straws but seeing as I already cooked off 1 voltage regulator, id hate to make it 2. Trying to cover my bases here.

 

[Ronmar]

Absolutely do NOt do that! First off you are an A1 and don't have a governor or run solenoid to hook to. Second of all they went to great length to insure the alternator was kept offline until after the engine is running(K11 that powers the alternator is controlled by the oil pressure switch and holds off enabling the alt/disabling the starter until the engine is running/oil pressure light is out)... The crap shown in the video insures the alt is online while you are pulling high starter current... might as well use the power system for arc welding while you are at it...

 

[Dexis]

Well as tempting as a new FREE WELDER sounds I guess I’ll just swap the new voltage regulator over and report back. Do I need to disconnect all the batteries to swap the regulator out?

 

[Dexis]

So I went and disconnected the exciter wire and started the truck up. Seemed fine at first except voltage was showing around 22V. Made it about 500 yards before trans started freaking out and dropping into neutral, I'm assuming now its getting hit with low voltage and cant function.

So now I'm wondering if my batteries need to be replaced as well. Hasn't that been an issue thats worn out charging system components on these LMTV’s?

Ive been reading all about this truck while working on multiple other vehicles for other people so I'm starting to lose track of what I've read where about what over the last few days. System overload.

 

[Ronmar]

Yea the dual volt alt was not the best idea, paired with the monster battery bank it was the kind of problem that class action lawsuits are made of in the real world. The 100A dual volt with the 14v side fully loaded only puts out @ 1930W compared to the 2800W of a straight 24V@100A alt. With the monster battery bank unless you run long hours you have trouble reaching full state of charge. That is the single biggest killer of lead acid batteries. Since the batts are always low, you are running the alt full out much of the time…

Cat specced a pair of group 31 batts for the equipment that uses these engines, thats what I run, I would recommend you drop to two batteries, which will be a far better match for the alternator.

 

[Dexis]

What would I have to do to switch to a pair of group 31’s? Any modifications and what about battery cable routing. Also is that something I can pick up at a generic auto parts store? Also I'm on 4 batteries currently, ive seen photos of guys who have 6. Not sure if that makes a difference.

Was trying to get this running for the 4th parade so a 4 hour round trip to the auto parts store tomorrow might be my hail mary if that might sort out the battery part. Or if the swap to a pair of 31’s is straight forward I do have a dozer that I might be able to cannibalize temporarily, it may have 31’s in it.

 

[Ronmar]

Group 31’s need box modifications, dropping to a pair if the 6t batts that are in there is probably the easiest. You may be able to charge and load test your 4 and find you have a serviceable pair right there already… since the truck has more 12 than 24v load, the 12v pair is often the pair that runs undercharged and fails first, with both of the 12-24v batts in better condition…

 

[Dexis]

Two issues I see there, first I dont have a load tester. Second is I'm not sure what I would do about the battery cables as they sit vs converting to two batteries. Here are photos of my current setup. Any ideas?

 

[Ronmar]

Ok, looks like someone already downsized the bank to group 24 batts. To drop to 2 batts is easy. Simply remove the terminals on a front(front of truck) or rear pair and tape over the disconnected terminals…

innermost terminals are 24v, middle 4 tied together are 12v outermost are ground…

You should be able to charge the batts and take them to an auto parts store to load test. If you need new batts, i believe a pair of group 27 batts will still set in the 6T pockets in the tray and those are a good match. 4ea of those group 24’s are also a OK match for the alt… Dropping to a single pair of group 24’s is starting to go a little low on the CCA scale but would probably work just fine for a long time in a warm-moderate climate.