Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 11, 2025 ...

Odd issue when downshifting

November 05, 2021, 02:42:24 pm

Noticed this the last two days of mountain driving. When I manually select fifth gear and full boost comes on. The trans does as requested and all is normal.

When manually or ecu auto selects fourth gear. When boost comes up. The engine cuts out one or two times within the first second after the shift. After that every thing is fine. No trans codes. Oil level good. Trans temp is normal (180-190F)

Fuel tank was at 5/8's. Outside temp was 60F.

I had once down shifted to third gear pulling a steep windy road out of Austin, Nv. No issues at all

This ONLY happens when shifting down into fourth gear.

Any ideas?

Quote Selected

Re: Odd issue when downshifting

Reply #1 – November 05, 2021, 07:20:54 pm

Speed sensor..?? how does it shift up in the gears especially 4-5 5-6.. underload any flareup ?

Quote Selected

Re: Odd issue when downshifting

Reply #2 – November 05, 2021, 08:11:08 pm

I agree with Hans. But also could be throttle position sensor if it has one. I had this happen on a 92 Dodge with a Cummins. Thought the tranny was going out.
Cheap fix
Chris

Quote Selected

Re: Odd issue when downshifting

Reply #3 – November 06, 2021, 12:18:19 am

It acts like it is hitting the over rev fuel cut off. After I posted this. We hit a really steep grade that topped out at 8,500Ft. I did a manual downshift from forth to third and it did it again. I saw the revs on the VMSPC hit 2000. (but wasn't staring at it) Yet another time I let the ECU downshift into 4th from 5th on a pull and it did fine. The trans up shifts just fine. The retarder is working great. As I understand the Allison ECU will not downshift if it will result in an over rev condition. The engine is electronically governed at 2,100 RPM. I'm not sure what the corp rev limit is.

No codes on the vmspc or shift panel. And with all the big pulls we have been doing in the last three days. We have been averaging 8.2mpg since leaving Walla Walla. Which is better than I usually get. So the coach is running pretty efficiently. Maybe I can go to a Cumins shop when we get to Tucson and have the engine ECU fuel cutoff parameters checked.

Quote Selected