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M1078A1 not charging in neutral! FIXED!

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RichCollins10

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Currently have an M1078A1 2320-01-447-6343, 2005 model. that is refusing to cooperate. Not charging in neutral, but charges in gear. Ran thru all the schematics and haven't had any luck. so far we have replaced batteries( it has AGM's in it), connections at the batteries and shut off solenoids, LBCD, every relay and CB in the PDP's, CTIS ECU, TCM, 100A Generator with Regulator ( w/ Led Lights), intake heater solenoid (old one was burnt up. The K40 Start Disable relay was overheated and practically welded itself to the Trailer B/O Relay right next to it in PDP # 3, so we replaced the entire PDP # 3 as well as PDP # 4 with known working good ones from another M1078A1, checking connections from K11 and K26 relays and everything checks out like it should. Low oil light goes off after start up, and we have good oil pressure. We have stepped the batteries down to 2 from 4 to try and see if the load difference would fix the issue/ no luck there. The only way we are able to have it charge is to remove the K11 Relay after start up, as soon as we replace it, no charge comes back on. K11 does not energize the alternator in neutral on wire 568A, only in drive. Regulator lights blink green when in drive, no lights in neutral. Been tackling this for over a week, any help is appreciated! What are we missing?!
 
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Ronmar

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K11 deenergized contacts provides the enable power to the regulator, so it will NOT charge without it in place. It probably also wont allow the LBCD to get an RPM signal from the reg to illuminate the No charge light if that is all you are using to gauge if it is charging or not...

I think this is an oil pressure circuit issue to the alt relay K11, as that is what controls the ground path to energize K11. The Neutral relay provides the power to K11 coil so it dropping into charge(removing K11 power) when you shift into gear points this to a K11 control issue(other side of coil shorted to ground keeping K11 energized even when oil light goes out).

Cant get to my drawings till this evening to suggest a place to check untill then...


What alt do you have in this rig? Unless it is the 260 amp, even a pair of the AGMs is a lot(they are wanting 54A from the 60/40 alt when discharged) when you include truck loads...
 
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RichCollins10

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Ronmar said:
K11 deenergized contacts provides the enable power to the regulator, so it will NOT charge without it in place. It probably also wont allow the LBCD to get an RPM signal from the reg to illuminate the No charge light if that is all you are using to gauge if it is charging or not...

I think this is an oil pressure circuit issue to the alt relay K11, as that is what controls the ground path to energize K11. The Neutral relay provides the power to K11 coil so it dropping into charge(removing K11 power) when you shift into gear points this to a K11 control issue(other side of coil shorted to ground keeping K11 energized even when oil light goes out).

Cant get to my drawings till this evening to suggest a place to check untill then...


What alt do you have in this rig? Unless it is the 260 amp, even a pair of the AGMs is a lot(they are wanting 54A from the 60/40 alt when discharged) when you include truck loads...
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That's what i had a thought about still.. ill try and dig in to the oil pressure circuit more. The oil pressure switch had been replaced as well, 3 pin connector type. I am assuming the problem will most likely lie between the Alt and the Oil Pressure Switch, not so much in the PDP?

It has the OEM Neihoff 100 AMP ALT on it, we have a few trucks here that had the same ALT ( 1 without LED's on the regulator). Trying to steer away from the 260A Alt due to funding costs.

Thank you for the response, and if you can get back about any more suggestions i would greatly appreciate it!
 
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Ronmar

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RichCollins10 said:
That's what i had a thought about still.. ill try and dig in to the oil pressure circuit more. The oil pressure switch had been replaced as well, 3 pin connector type. I am assuming the problem will most likely lie between the Alt and the Oil Pressure Switch, not so much in the PDP?

It has the OEM Neihoff 100 AMP ALT on it, we have a few trucks here that had the same ALT ( 1 without LED's on the regulator). Trying to steer away from the 260A Alt due to funding costs.

Thank you for the response, and if you can get back about any more suggestions i would greatly appreciate it!
Click to expand...
It will be between oil sw and K11. One side of the K11 coil gets power from the neutral relay, the other side goes to ground thru the oil pressure sw like the dash light does.

When you go over 15PSI oil pressure that sw opens turning off the dash light and breaking the circuit to K11 deenergizing it. A deenergized K11 then can feed 24v to the alt reg to power it. That part is working if the alt comes online when in gear so I suspect a short on the K11 to oil switch path. I think there is a steering diode in there somewhere but will have to look it up in the drawing this evening.

the 100A alts are nearly as expensive, and too much battery will cook them also. Drop to two batts on these trucks and keep a trickle charger on them when parked...
 
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Ronmar

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Ok, now I remember that circuit. On the A1 they simplified things a little by combining the starter lockout and alternator excite function onto K11. When K11 is energized, the starter is enabled, the alternator is disabled. When K11 de-energizes above 15PSI oil pressure, the starter gets disabled and the alternator is brought online.

The potential problem with this, is that on a long cold weather crank, the engine might actually build enough oil pressure while cranking to open the switch and disable K11 before the engine is running, which would halt the start…

To prevent this, they added a latching circuit(circled in red) that samples start button 24V and energizes T2(not sure what that component symbol is, probably some form of SCR) which provides another path to ground to insure K11 stays energized no matter what the oil pressure sw does, to power the start circuit untill the start button is released.

I suspect that component T2 in that circuit I circled in red may be shorted. You can confirm this by pulling K11 with the truck running(no oil light lit) and measuring resistance from the relay socket pin 85 to ground. I suspect you will find a low enough resistance to ground to keep K11 energized even after the oil sw has opened and start button is released. It is because of this circuit they added diode D11. It keeps that circuit from effecting the low oil light, otherwise it would stay lit untill you released the start button. That is also why the problem is probably that circuit. If there was a short to ground anywhere after diode D11 it would also effect the low oil light in the dash, keeping it lit all the time…

Pretty sure they could have done this with a relay, so I am not sure why someone felt the need to get fancy with this type latching circuit…

271F9863-F749-4166-BF5F-D58A2094D5CD.jpeg
 
R

Ronmar

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When analizing a circuit you need to decide if it is bad, or if it is being told to do its job improperly(garbage in = garbage out).

If you find the short/path to ground on pin 85 of K11 is from that latch circuit, I would also confirm that there is NO voltage on the source/sensing side of that circuit where I wrote the note “24v from start sw”. You can do this easiest by pulling K53 pin 86 with the ignition on, and looking for any voltage at that pin Measured to ground. K53 is the radio power relay and it opens the radio power circuit while cranking the engine/starter. It should only see voltage when you push the start button.

I have no idea how much voltage that latch circuit needs to trigger, but Something like a partially/high resistance shorted auxiliary start switch down on the frame rail, might put a low voltage on the start circuit that is enough to activate that latch circuit, But NOT pull in the aux start relay and crank the engine… if you find voltage on that circuit you need to find its source, and the frame rail start switch down by the passenger front tire is a prime candidate for that.

If that latch circuit is indeed bad/T2 shorted, I guess you have a few options:
1. You can identify the bad component(probably T2) and replace it.
2. You can replace the entire PDP circuit board.
3. You could remove T2 and wire a normally open sw across its connection points on the circuit board, and label this sw “Cold WX Start Assist”. The 3126 starts pretty easy even when cold so you are probably rarely if ever building enough oil pressure to drop out the start circuit Before engine start.
4. If you are not using K53 to power a radio circuit, it could probably be re-configured to provide that starter latching circuit to ground that the component T2 and its associates now provide.
 
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RichCollins10

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I appreciate the input, but unfortunately i believe this does not apply to this truck. I should have mentioned that the serial number for this truck is ending with 102320 and it has the 4 individual PDP's or (PDM's) as the schematic labels them. they switched from the PDP to the PDM's after S/N 99,999. It does not have a single PDP for the whole circuit, which in turn means there is no T2/latching circuit ( unless it is something entirely different within the PDM). so replacing that is out of the picture. We have swapped the individual PDM's and had no luck. Still attempted to run thru some of the T/S you described and we had low resistance testing pin 85 on K11 to ground with the truck running. Checked voltage at K53 pin 86 and received about 26V only when the start button was pushed like it should. Eliminated the frame rail switches completely by disconnecting the plugs to the ignition and start switches, still had no effect on the charging issue. I have attached a picture of one of the schematic's we are using for this truck.


M1078A1.jpg
 
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Ronmar

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Oh, if it has the C7 engine then you have what is known as an A1R… you did say it was a 2005? I should have asked… Yes, different control circuit, but still a lot in common with the older A1 circuit. I believe it uses a module associated with the MMDC(gauge controller) to deliver the oil pressure OK signal to lockout the starter and enable the alternator above 15PSI. There is another relay involved with it, K40. Drawings are at home I will have to review this afternoon when I get there. Looking at your drawing if K40 was bad(unable to energize), it would keep the ground to K11 in place which would keep K11 energized and the alternator offline until you come out of neutral and remove the power input to K11s coil.
 
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RichCollins10

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Ronmar said:
Oh, if it has the C7 engine then you have what is known as an A1R… you did say it was a 2005? I should have asked… Yes, different control circuit, but still a lot in common with the older A1 circuit. I believe it uses a module associated with the MMDC(gauge controller) to deliver the oil pressure OK signal to lockout the starter and enable the alternator above 15PSI. There is another relay involved with it, K40. Drawings are at home I will have to review this afternoon when I get there.
Click to expand...
Sounds good, and yes it is a 2005, MFG date 09/05.

Attached the MMDC Sheet for reference to match up with what you have.

Again, Thank you for taking the time and helping us with this.


M1078A1-1.jpgM1078A1-2.jpg
 
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GeneralDisorder

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coachgeo said:
Congrats on the fix......

now off topic hmmmmm??....... vewy interesting.. "No delivery date" stamped on that plate. Does that mean the truck never left Sealy/ever taken possession of by Military?
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Seems to have no significant meaning. My truck has no delivery date and was in Kuwait (import tag on the inside of the van door) and then purchased from the military out of El-Paso. I found a military railhead checklist signed by a SSG in one of the interior cargo boxes behind the seat. Also a few sunflower seed shells and the usual trappings of PVT Snuffy (several things ham fisted, installed wrong, pulverized, damaged, lost, and all services triumphantly neglected) - also PLENTY of sand.

Likely supposed to be filled in by the unit when they take delivery to document when the warranty starts (yes military hardware has a warranty from the manufacturer) and most of the time they just don't bother. But that's probably the intention I would guess. Like many things in the military this gets overlooked or pencil whipped.

2008 M1079 A1R Data Plate.jpg
 
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LmtvPR

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RichCollins10 said:
Currently have an M1078A1 2320-01-447-6343, 2005 model. that is refusing to cooperate. Not charging in neutral, but charges in gear. Ran thru all the schematics and haven't had any luck. so far we have replaced batteries( it has AGM's in it), connections at the batteries and shut off solenoids, LBCD, every relay and CB in the PDP's, CTIS ECU, TCM, 100A Generator with Regulator ( w/ Led Lights), intake heater solenoid (old one was burnt up. The K40 Start Disable relay was overheated and practically welded itself to the Trailer B/O Relay right next to it in PDP # 3, so we replaced the entire PDP # 3 as well as PDP # 4 with known working good ones from another M1078A1, checking connections from K11 and K26 relays and everything checks out like it should. Low oil light goes off after start up, and we have good oil pressure. We have stepped the batteries down to 2 from 4 to try and see if the load difference would fix the issue/ no luck there. The only way we are able to have it charge is to remove the K11 Relay after start up, as soon as we replace it, no charge comes back on. K11 does not energize the alternator in neutral on wire 568A, only in drive. Regulator lights blink green when in drive, no lights in neutral. Been tackling this for over a week, any help is appreciated! What are we missing?!
Click to expand...
Hi I have a 1078a1 with some electrical issues and wondering if you have a picture of the sticker that goes under the dash to tell the relay locations. I want to check the k11 and k26 but don’t know their location because my sticker is damaged and can’t find any info online. Thanks .
 
Third From Texas

Third From Texas

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LmtvPR said:
Hi I have a 1078a1 with some electrical issues and wondering if you have a picture of the sticker that goes under the dash to tell the relay locations. I want to check the k11 and k26 but don’t know their location because my sticker is damaged and can’t find any info online. Thanks .
Click to expand...
Do you have the TM? I *think* that the CB/relay image is in there.
 
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