Just got the car put together enough to try my new 145mph speedo out on the jack stands. To my utter surprise the things is jumpin around and reading all the way up to 135mph in first gear and thats just up at no more than 2000 RPM in first gear on the new motor.
Mind you, everything on the car is modified... prom, new 383, Accel 300+, T56 swap, rear end, etc., etc., so I am unsure as to where to look. I am guessing the prom programming is off somewhere for the speedo calibration? I just bought the instrument cluster off of eBay and the rest of seems to be working fine. Could it be the VSS at the tranny? If I look at the .bin file to find some answers, what should I be expecting to see and where?
Thanks

 

I'm adding no technical information so don't be alarmed, but that is by far the best saying i've ever heard, I feel the same way......:rockon:

 

did you just connect the T56's orignal VSS to the wiring?


the fbody T56's VSS has a MUCH higher resolution then the 3rdgens tranny mounted VSS..

so when its sending a signal that VSS thinks means 10mph, it could be what the speedo thinks 90mph....

 

Yes I am using the one that came on the T56. Is this the prob? So I am going to need a T5 specific VSS?

 

I think the number of teeth on the wheel is different. Which would make it do that. Check with the tranny board or the place that sold the trans to you. The output shafts are different sizes so you can't just swap them.

 

I think you might need a buffer, not real up on the electronic speedos but I think the 4th gens used a 4000 pulse per minute VSS and 3rd gens used 2000 PPM. Someone speak up if this is incorrect.

 

Nope

T56's put out 40,000 ppm where as his 91 used to put ou 4,000 ppm

If you burn your own proms, and use tunercat, set the road speed constant/vss raito to 40,000 and then mess with the instrument pannel pulse divider. That will get your speedo working and what your ECM is seeing for MPH.

Kat

 

Ok thanks for the info. Looks like I'll be crackin numbers some numbers again... From what I have read its going to take some trial and error. Don't we all just love guessing games?