Fixing pulse divisor with T56 and 40,000 ppm vss, got ecm right but speedo not.
I was able to take vss ppm value to 50,200 and get ecm to read correct, but pulse divisor only goes to max value of 292 and that has me off still on speedo by about 25 mph..

Anything I can do about this?

Using Tunercat..

 

What about using one of those Dakota Digital convertor boxes...? Fairly cheap.

No affiliation with DD. I used one for different project, worked for me.

 

Well thats an option, but why if I can fix it for free

I have it also closer than it was, just seems I need more.

 

My T56 swap using the SGI-5B box worked out fine last week. I didn't have enough free time to spend playing with the divisors like you're dong, so I went the lazy route and used the Dakota Digital box.

As reported elsewhere on these forums though, the instructions are wrong, and their tech support didn't give me any helpful info either.

I had to have BOTH switch #3 and switch #4 on with the output wire to the ECM coming out of OUTPUT #3 to get a compatible signal on my 91. Then it was just a matter of finding the right setting to get it correct.

 

The best you can do is get the speedometer to work as if you have 3.42's or numerically lower. Since you have higher than that, I dont know of anything in the ECM you can change.
What I did was machine the tailshaft to accept a 90-92 magnetic speedo unit. I cant find my pic of it though.

 

I was looking for something else and found this. Hopefully it will help you out.

1992 F-body TPI 1227730 VSS re-calibration after a T-56 swap

 

Thanks alot,
I actually mailed tunercat and they replied:

each value represents a divider for the speed pulses sent to the speedo as follows:

Divider IPP Value

1 = 0
6 = 128
7 = 64
8 = 192
9 = 32
10 = 160
11 = 96

So I though that the values were linear to theire actions, not the case.
So value 160 shoulf fix me right up.

Thanks all for help
and hope this helps someone as it did me


- I did come across that page atomic and thank you!.