Problems M1078 A0 voltage collapses

[Ecki]

Hi guys,
I'm new here and come from Germany.
My friend has a M1078 A0 and the following problems.
The truck just shuts down while driving as if the voltage breaks down, but starts up again immediately afterwards.we have the feeling that it usually happens when it is very warm.does anyone have an idea what this can be.maybe it is a known problem and you can help quickly.

Greetings from Germany

 

[Ronmar]

You have 3 paths to follow. Start at the batteries, follow the ground wire hand over hand to the inst shunt, then on to the front of the starter motor, then the strap over to the drivers frame. Next check the alternator ground strap, then the cab ground strap from passenger frame rail to the cab(behind,grill. Disconnect, clean and re-assemble each and every connector.

Next follow the 12v lead to the polarity protection device(inboard of spare tire. The 12v forks there, one goes to the alt one goes to the power panel. Again clean and re-assemble every connection.

last is the 24v leads. It forks at the battery, one goes to the starter solenoid, the other goes to the polarity box, where it again forks, one to the alt and one to the power panel…

good houses have good foundations, and this is the electrical foundation of this vehicle…

its a mechanical diesel, if it drops 24v, the run solenoid on the governor will relax and shut-down the engine. Check the connections on that solenoid.

if the clean and inspect does not cure it, you really need to note exactly what is shutting off. Trans display, ctis, does the fan control solenoid vent air like it does when you shutoff the ignition?

The A0 is weird in that it uses 12v to power the 24v ignition relay, so if the 12v load connection from the polarity protection device drops its output, it will act just like you shutoff the ign sw…

 

[Ecki]

You have 3 paths to follow. Start at the batteries, follow the ground wire hand over hand to the inst shunt, then on to the front of the starter motor, then the strap over to the drivers frame. Next check the alternator ground strap, then the cab ground strap from passenger frame rail to the cab(behind,grill. Disconnect, clean and re-assemble each and every connector.

Next follow the 12v lead to the polarity protection device(inboard of spare tire. The 12v forks there, one goes to the alt one goes to the power panel. Again clean and re-assemble every connection.

last is the 24v leads. It forks at the battery, one goes to the starter solenoid, the other goes to the polarity box, where it again forks, one to the alt and one to the power panel…

good houses have good foundations, and this is the electrical foundation of this vehicle…

its a mechanical diesel, if it drops 24v, the run solenoid on the governor will relax and shut-down the engine. Check the connections on that solenoid.

if the clean and inspect does not cure it, you really need to note exactly what is shutting off. Trans display, ctis, does the fan control solenoid vent air like it does when you shutoff the ignition?

The A0 is weird in that it uses 12v to power the 24v ignition relay, so if the 12v load connection from the polarity protection device drops its output, it will act just like you shutoff the ign sw…

Hello and thank you for the quick reply.
The ground wires have all been cleaned, as this was our first assumption.
Could it possibly be related to the polarity protection? An electrical schematic would also help, can you get one of these anywhere? Unfortunately there is little information available in Germany for this truck.
Thank you

 

[Ronmar]

it could be a PPD issue, but I doubt it as is just a set of diodes and quite robust. The only issues I have seen with them are due to corrosion at the terminal studs as it is out in the weather. Don’t recall a diode failure. Clean all those therminals…

The A0 manuals are available here on this site. There is a schematic in the back of each techmanual.

M1078 TM's

Listed below are a number of the TM's for the M1078 trucks. To save them to your computer, right click, select "save as" m1078_TM 9-2320-365-10.pdf TM 9-2320-365-10 for the M1078 series trucks. m1078_TM 9-2320-365-20-1.pdf TM 9-2320-365-20-1 for the M1078 series trucks. m1078_TM...

www.steelsoldiers.com

 

[coachgeo]

.... An electrical schematic would also help, can you get one of these anywhere? Unfortunately there is little information available in Germany for this truck.
Thank you

@Ronmar was kind enough to link it for you. For future reference .. the forum with all the manuals (Technical Manuals) is page one of this whole Discussion Board's forums. Home / Forums / Technical Manuals / pick your vehicle FMTV in this case

 

[Ecki]

Hello and thank you for the quick reply.
The ground wires have all been cleaned, as this was our first assumption.
Could it possibly be related to the polarity protection? An electrical schematic would also help, can you get one of these anywhere? Unfortunately there is little information available in Germany for this truck.
Thank you

it could be a PPD issue, but I doubt it as is just a set of diodes and quite robust. The only issues I have seen with them are due to corrosion at the terminal studs as it is out in the weather. Don’t recall a diode failure. Clean all those therminals…

The A0 manuals are available here on this site. There is a schematic in the back of each techmanual.

M1078 TM's

Listed below are a number of the TM's for the M1078 trucks. To save them to your computer, right click, select "save as" m1078_TM 9-2320-365-10.pdf TM 9-2320-365-10 for the M1078 series trucks. m1078_TM 9-2320-365-20-1.pdf TM 9-2320-365-20-1 for the M1078 series trucks. m1078_TM...

www.steelsoldiers.com

Thanks for the link, that helps. Unfortunately the electrical circuit diagrams are not complete, there is always a page missing or is there a trick when downloading?

 

[Ronmar]

Thanks for the link, that helps. Unfortunately the electrical circuit diagrams are not complete, there is always a page missing or is there a trick when downloading?

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