Well, 2 weeks after installing my new APPS, the truck is bucking again. Let me try to give a more detailed description. If a am accelerating with no more than 1/3 throttle between 50km/h and 90 km/h the power surges up and down fairly agressively. It bumps the rpm up and down by about 300 rpm. If I drive on level ground between 50 km/h and 90 km/h it still pulses up but only about 200 rpm. If I accelerate moderately hard with more than 50% throttle, everything is smooth. I got the first return of the symptoms since APPS replacement yesterday. I did an APPS reset last night and that was good for a 1hr drive up some hard mountain climbs and all was good. Once I dropped off the 3,000 lb trailer and started home the bucking / surging started again. If I drive on level ground at about 80km/h it is really bad. If I lock-out O/D and stay at 80 km/h I have no symptoms but it is revving about 2200 rpm. That cure isn't sustainable

I think I have explained the symptoms as best I can. I pulled the codes - it was clear of codes 3 days ago. I have the following codes:
P0234 Turbo Overboost
P1693 - My code reader says there is a matching code in the ECM and Transmission module.

So, any thoughts folks?

The symptoms are by no means definitive for a dying VP44 and it is a pretty expensive part to just throw at a problem.

 

it sounds like it's bouncing in and out of o/d prematurely. Usually caused by a bad governor pressure transducer, or perhaps electrical interference. If you have a heavy foot, it keeps the line pressure high enough for the tranny to shift properly, but go easy on the throttle, and it is getting confused.

Then again, I probably don't have a clue what I'm talking about, it is simply a starting point. Do some pressure checks on the transmission, while running it down the road.

Use two people for that last part.

Good luck

 

Pind, I confirmed today that my prob is the T/C unlocking and then locking again. I assume it is going to be the well documented problem with electrical noise, so I am going to go hunt down the info about where those grounds are. The problem is happening in 3rd and 4th (OD) gears. Would this governor pressure transducer you mention cause the T/C to lock and unlock in 3rd and 4th gears or would it just cause it to shift between 3rd and 4th erratically?

There are 2 reasons I ask, 1 it sounds like finding all the grounds can be a pain. Second, the T/C lockup problem seems to go away once I am above 90km/h or 2,000 rpm.