BBC632Camaro

iTrader: (82)

I'm finishing up a ls1/4L80e swap into my 66 impala with a standalone harness and tune made for my setup. I was having problems with it shifting too soon. I've come to find out my vss readings are way off. I've corrected some things and gotten it better but still way off. Long story short after researching and playing with it for days, I'm sure i've got the right numbers in it now but its still off. Here's what I got.. I actually used a gps to find out my real mph and a calculator to figure my gears are really 3.36 and they are.

255/60R15 Tires: 26.26"
3.36 Gears
vss pulses/mile: 103222
vss pulses/rev-trans: 40
trans revolutions/mile: 2580.5858

For some reason the pcm thinks its going faster than what I really am. IIRC it was reading 94mph when I am going a true 65. WHAT COULD BE CAUSING THIS?? Is the problem in my tune or harness I got or could it be a vss sensor?

Old Geezer

iTrader: (3)

I just ran the size and ratio thru my EFILIVE calculator. It came with this info:
Tire diameter = 27.05"
100,317 pulses/mile.
Vss pulse/rev = 40.
TOS rev 2505.43

BBC632Camaro

iTrader: (82)

I gave those numbers a try and it made it worse. 65 was 107 on the pcm. I've traced wires and they seem to be in the right spots. Bad vss sensor maybe?? I installed a transgo hd-2 shift kit and new black pressure solenoid in the transmission but everything seemed to go pretty smooth. Also I'm not so sure the converter is locking. Another guy thought maybe it was locking all the time. Could any of this affect the vss though and how it reads?

daniel76309

I don't know if this will help, but I think there are identical front and rear VSS's on the 4L80E. If you are only using one of them for your PCM input, you could switch them and see if it makes any difference. (If it doesn't change anything, it would pretty much eliminate the VSS as the cause of the problem.)