Allison 5sp: Slipping or somthing else?

[Chris611]

A couple nights ago I was trying to build boost with my pulling truck in the driveway. I was power braking and launching, etc... At one point I hit the throttle and the engine rev'd, but the truck barely moved. The "D" on the shift indicator was flashing. This happened in wet grass on a hill. I shut it off for a few minutes and started it and it seemed to be fine. The only code I had was a TCM P0880, which from what I can find means the TCM lost power. I cleared this code. The code could have been from some time ago, not sure. So I thought all was good. I hooked to the sled yesterday and when I took off, the RPM's went up and the truck was barely moving. I logged the trans in the pits and attached the logs here. I could easily drive it on the trailer. It's only when you really start pushing on the throttle does it them rev with no go.

Truck eng/trans is stock with EFILive tune. Have 30+ hooks on it this year with basically the same tune and have not had any problems.

Truck shows no codes. No check engine light, fluid is bright red and doesn't smell burnt.

NSBU?

Any help would be great.

Thanks guys.

 

[Chris611]

Any ideas? What would cause the trans to feel like it slipping and set no codes?

 

[jraymer]

My truck did the same thing when my batteries died and I had to jump start it. I put it in park and ran it for a few minutes then I shut it off, turned it back on and it is all good. Did you have a loss of electrical power when it happened?

 

[Chris611]

No loss of power lately.

I just pulled the pan on the transmission. Fluid is bright red. There is no debris in the pan. The internal filter was still in place. I tugged on all the wires and nothing looked loose or damaged.

I'm lost. It seems like it is something electrical, but just can't figure out what. The fact that I don't have any codes is puzzling.

 

[SteveFord]

As easy as it is to get to I would try and swap out your nsbu with another one.

 

[jraymer]

I had one code when it happened to mine, some power loss code or something. The indicator on the dash just flashed. I think its some shift range inhibitor or something? I don't know much about it, someone else will probably post some better info on what is going on.

 

[Chris611]

I did have a power loss to the TCM code. But I didn't know if it was old code or not. I've pulled the neg battery cables probably once a week for the last couple months. Been welding on the chassis (chain loops, pulling hitch, traction bars, etc...always something) and I pull the neg on the batteries every time.

I guess tomorrow I will run into DSM and get a NBSU.