Originally Posted by BeatMarti (Post 11983583)

12B34 is for the chassis-cab truck (F450/F550) with the conventional turbo.

I updated it a couple of days and 250 miles ago. Sure, not a lot of miles to show a significant difference in mileage. It feels as it might have gone down a little but the jury is still out.

However, I very much like the much improved shifting and better dead-start response. Dead start acceleration is responding quicker and once taking off, a lot more "measured". I used to wait for seconds on a green light with no activity and then just about leaving rubber. Now, it starts quicker and smoother.

Shifting is more "aggressive" (slightly higher shift points) and that is most likely where the fuel mileage drop (if any) comes from. I also noticed a change in "power curve". It seems more "peaky" starting from about 2300 RPM up, but feels like less power below that. I also noticed that the turbo boost has gone up by about 2 psi. I now regularly reach/peak at 28 psi during acceleration.

Another interesting change is the downshift during slow deceleration approaching a red light or whatever while in NORMAL transmission mode. I noticed that based on SPEED (not RPM) the tranny shifts down from 6-5-4-3-2-1 which is great because if for example the light turns green and you want to accelerate, it is already in the correct gear. That one is new to me and I sure like it.

I believe they moved down the de-fuel point reacting to exhaust temperatures that may be a bit lower than before. That would make sense since one of the items they tried to fix is turbo blade failures.

Originally Posted by hay is for horses (Post 11983778)

This tsb also is for f350 chassis cab and mine goes in on Monday. I have been discussing this recal with another member who had it done on a chassis cab and he has noticed no difference in fuel or truck behavior. I will update when mine is done.