First off....Long time reader first time post.....Interesting problem that i have, recently swapped in a T56 and went with the dakota digital box....works great so i thought. My speedo is dead on I mean no problems at all rock steady, no jumping, mile markers are on the nose the whole bit. Now the problem...Recently got into prom burning. I load datamaster and start my data logging. Look down im doing 85 on the freeway part throttle, glance over at the laptop and low and behold it shows me at 255 mph. after getting to my destination and review of the log I can see that my MPH is all over the place 0 -255 and everywhere in between. Ok here is the question how can my Speedo by spot on and the ecm not see the same thing. I thought the ecm feed the info to the Speedo? If im worng what can be done to correct the false ecm readings. Im sure this can't be good for the ecm to see such drastic changes in MPH.

I have seen some info on making the changes in the Prom code to delete the DD box, and I might do that if the DD box just ain't gonna work.

BTW I have checked all my connections to the DD box just to make sure there weren't any loose connections, but like I said the Sppedo is rock solid.

TIA
Chris B

 

Chris,

Can we put your volts meter on tach mode & see what the tranny is feeding the Dak box and what the ECM is being fed from the Dak & what the ECM is sending the speedo? Lemme know, and answer your cell

Matthew

 

TTT

 

Did you change the pulse per mile constant in the chip? I would try that and see what happens. it should be 40000 with a T-56.

 

I can't believe you didn't change the ECM.