I recently switched from 730 to 749 ECM and I noticed that my displayed vehicle speed in DM is way off (low) compared to speedo. I have the constant set to the same PPM (4007) I had it set to in the 8D bin. Any suggestions?

 

hmm there are some different VSS wiring schemes you could encounter code wise and wiring wise. please explian your current setup. magnetic or optical ? i belive you have a magnetic but i dont know what year your car is.

 

It is magnetic. I purchased the adapter from JTR when I installed the automatic. I believe it is a 4 ppr sensor. My speedo seems to work fine and accurate and in my old DM logs with the 730 it was on with the speedo. It has only been off in the ecm since the swap. It is an 88 corvette.

 

I noticed today that the computer displayed MPH is half of what the speedo is displying, should I double the PPM or split the number in half for my constant?