Tune vs Speedometer

1988GTU · 08-14-2008, 02:30 PM

When I was sent a file to try I ended up loading it up and taking it for a spin. Ever since then my Speedometer is off 30 mph it seems. What areas, suggestions does anyone have for me to try or adjust? IIRC it was a modified tgp code that I am using in a 88 Beretta with the 7730.

**bszopi** · 08-14-2008, 02:33 PM

You need to adjust the PPM (pulses per mile) value for the VSS to match your tranny. What the value is, I can't tell you. But that is probably where your problem lies.

1988GTU · 08-14-2008, 02:48 PM

I just did a search and found this tid bit:
Calibrating the VSS

your speedo may be off once burning the TGP chip. mine was and I was able to fix it.

you need to find what the "VSS Road Speed Sensor Constant" and "VSS Pulse Divisor" were on your stock chip.

this is under constants/scalars.

having the correct VSS settings is especially important for autos, since the TCC will not work correctly if the ECM is being told the wrong speed.

Thanks for the fast response bz.

z34phoenix · 09-07-2008, 08:45 PM

very true and part throtle shifts will be off aswell.

i have a sheet from DHP that can calc a new PPM just get me the old ppm stock tire size, stock tire dia and new and old final drive ratio and i think that is all it needs to calc the new ppm

Superdave · 09-07-2008, 09:46 PM

his trans isn't electronic...

1988GTU · 09-07-2008, 10:00 PM

I have it so far under control. Now I am just giving it a better tune. It runs rich right now, but all I can do are little steps at a time... I hate tuning!!!!

Just hope this trans can hold out until Next Spring.