I'm tuning a 24000 vss to a fiero. I'm running 14" tires and have had to adjust the road speed constant in $88 to about 26000 to calibrate to actual road speed. No problem there.
The problem is:
The speedo is fed not from the vss, but from the ecm (7730) which converts and then divides the signal to 4000 so my Speedo can use it. However, when I calibrate the constant, the Speedo still reads the same, no matter what. So it always reads 8% more than actual.
I don't understand this because the signal is generated by the ecm....or at least i thought it was, but it looks instead to be simply filtered via hardware.
Question :
Is there a way to adjust the ppm out from the ecm to make my Speedo read correctly?
Ron