Okay I've been trying to recalibrate my DRAC, something I've needed to do for a long time but I just recently was able to get around to it.

I popped my gauges out, removed the microfuse thingeys, crunched the numbers for the input ratio and soldered in two jumpers where I thought they were supposed to go.

Well long story short the speedo is now probably 10 MPH under instead of 10 MPH over like it was. Can someone help me out and tell me what I'm doing wrong here?? I've gone over and over the numbers but can't figure it out :Confused:

Here is the formula I used to figure my Input Ratio:

63360 x Gear Ratio(4.88) x pulses per revolution of speed sensor [40]
tire rolling circumference in inches(93.9015748) x 128000


The tire circumference is figured based upon a "worn" 265/70/R16 tire.

Figuring all this gave me an Input Ratio of:.97182


So going to the chart towards the bottom of this page : http://www.tbichips.com/drac/

I referenced the chart and installed jumpers in 1 and 6 just like I was supposed to.


Also, I was assuming this was right, but the #1 spot is on the TOP like in this picture right???



Can anyone please help and shine a light on this for me??

 

Okay I think I figured it out, I'll post what I found in case it might help someone later who searches for a similar question.

I went back over my figures and realized that I had indeed been making a rather stupid and easy mistake with the math. I was dividing the top number of the equation into the bottom rather than the bottom number into the top.

Plugging my numbers back into the equation and dividing them the right way this time gave me

12355200
-------------
12064000 ========> 1.0241379

Well this figure(1.0241379), is the proper input ratio for my setup. But, the highest possible input ratio for the DRAC is .988770.

Given that the REAL input ratio that I NEED was not in the range of possible calibrations, I knew it wasn't going to be EXACT. But, I soldered the jumpers in 1 and 7 as specified for the 0.988770 IR(InputRatio) hoping it would be close enough.

After buttoning it all back up and going for a test drive my speedometer is close, real damn close. It's within 1 or 2 MPH. Success!

Well I figure it's good enough this way, and it's the closest I could get it with this ancient TBI technology