M931a1 no power while in gear


Excuse me if this has been covered before a buddy of mine just scored a really nice m931a1 with the nhc 250 motor in it for 4000$ its sitting in my driveway next to my m931a1 i believe he was already in contact with Wes Simpson and he believes the truck is sucking air into the fuel. So here is where we are at the moment trucks transmission was drained new fluid and filter added we dropped the fuel,filter added newfuel filter and additive to the diesel truck starts up amazingly well and idles without skipping a beat while,it is in,neutral you can rev it up to redline no problem and acts as it should you drop it in gear and it becomes and sluggish as can be push the accl to the floor and truck struggles to move anyone know anything? Or did he just buy a crapper lol trying to get this going so it leaves my yard



Feo, Fuerte y Formal
Supporting Vendor
Mason, TN
other symptom was that "he was driving it the other day and all the sudden it opened up like nothing was wrong" and i assuming drove fine? he said it struggles on any incline. I did not know it was on flat ground. it is a NHC250 so on any hill its gonna slug but if its that bad it is noticeable.

You can add a fuel test gauge ( up to 600psi liquid filled) and plug it in to the 1/8" pipe port on the fuel solenoid and run it into the cab and see what kind of pressure you are getting on the truck with a moving load on it. This will monitor rail pressure from the pump to see if it is a bad pump but i wouldn't assume so with it having been replaced before.


The Person You Were Warned About As A Child
Super Moderator
Steel Soldiers Supporter
Monrovia, Ca.
Look at the throttle lever, make sure it is breaking over or not loose on the shaft.


Well-known member
Steel Soldiers Supporter
Leesburg, GA
I had a similar issue when the front seal went out on my injection pump and filled my crankcase with a few gallons of diesel. Left the house and my truck was running strong, shifting through gears and acting "normal". I made 2 stops and headed home. I made the turn onto a 4 lane road about 8 miles from my house and the inside filled with smoke which made me pull over. The truck was feeling sluggish making that turn and flooring the throttle didn't make much difference. In my case it was a failed injection pump. It happened suddenly and it did not help at all that the military chose to block off the weep hole on the coupling. Diesel would normally drain out from there instead of making it's way into the oil.
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