Z06ish

I put a 09 3.42 diff into my a4 05 car. I used to have 2.73s. Changed the tune to reflect the new gears however when I accelerate the speedometer and HUD stays on 0 mph until I let off and then the speedometer will
jump instantly to the correct speed. We changed the swapped out the vss sensor on top of the diff and the same thing happens. With hp tuners the vss speed and actual speed both read the entire time, but do not match, does the ECM read from a different speed sensor/table when accelerating vs coasting? Anyone seen this before?

Joe_G

If he doesn't chime in, PM Dennis50nj. He dealt with this in his 05 and I've seen him post about it in years past, I think he figured it out.

Z06ish

I contacted him and he indicated it only happened at hard launches at the track. I have found other threads that indicate that seems to happen at the track on 05's with large stalls etc. My issue seems to be a little different as my speedometer drops to zero on pretty much any decent acceleration on the street. My setup consist of a 05 cammed supercharged LS2, RPM built 4l65E, Circle D 3200 stall and an 09 3.42 rear end. I had no speedometer issues until I swapped to the newer style rear end. I only swapped because my 2.73s in my 05 rear started to whine pretty bad. Anybody?

dennis50nj

mine did it with the gear change and it will do it on a faster launch on the street it doesnt have to be a race, just leaving a light or stop sign quick, it will read no mph until i let off the throttle, i think its the after market gears,

Z06ish

With the help of Todd at RPM Transmissions and Victor at VZ Autoworks, we finally got it fixed. It is a tuning issue and has to do with HP tuners and the "odd" 05 computer. I do not know the exact fix as there was quite a bit of trial and error, but all the tables have to be manipulated manually, not utilizing the auto configuration features within HP tuners. Traction is an even bigger issue now going from 2.73s to 3.42s with my setup, but at least I know how many MPH my rear tires are spinning at and it shifts correctly.