I'm trying to help a friend get his speedo calibrated on his 89 Chevy pickup.
Some one before him put 29" tires on the truck and the speedo is too slow.
The trans has the magnetic pickup, so the gears can't be changed.
I would assume that there would be a place in the bin file for the 747 to make a change.
Any help would be appreciated. I searched and found lots of answers to change gears in trans, but this is a magnetic one.
Thanks,
Ron

 

maybe I can help you here. I put a 5 speed manual trans from an 89 or 90 pickup and know the magentic pickup you have. I don't believe the 747 ECM allows the changes you want to make. (but if you find a way to do it, please let me know!!)

But there is a module in the dash that allows for recalibrating the speedo. I had to use that part of the dash to make the ECM see the right speed in my 85 truck. I was able to research the module and it basically came down to cutting or jumpering pins on the circuit board. SOmewhere I have this, if you can't find it (try GOOGLE) and I can go through my stuff. Good luck.

 

The 7747 does not support changes to the speedo. That's all handled thru the VSS and gears.

 

I think Greg is referring to the DRAC module modifications to get different outputs.
Do a search on "speedo-calibration" and or DRAC modules
Stupid link won't work even though I pasted it directly.
Might have what you're looking for.

 

I should have know that it is the same basic thing as the 3rd gen stuff, duh. I'll try to find it tomorrow.
Thanks a million guys for the help again.
Ron

 

Go to the DIY-EFI FTP site and look for a file called Drac2.pdf . It has all the info you need. HTH

 

DRAC Calculator Page

 

I don't believe the DRACs were used in the trucks until 92.

Search some of the truck forums and you'll probably find what you need.