hotrodf1

Hey all,


I swapped a 93 LT1 (with the ECM) and T56 into my 91 RS. I have the software / hardware to tune it, and have done that, still a work in progress.


The speedo does not read correctly. The internal speed as calculated by the ECM is correct within 1 mph, using laptop and GPS speedo to compare.


The Bin I started with used a Instrument Panel pulse divisor of 96. Speedo read very low. I tried a 75 or so, which made it better. Then tried 65, which didn't seem to change it. Now I have a 35 in there, and the speedo still reads low. When going 60, the speedo reads 40-45, forget exactly.


Anyhow, I can't figure out why change the pulse divisor isn't getting me the results I wanted. Kinda clueless what to try next. I don't see any other speed related variables in the BDLD bin to change.


Furthermore, the LT1 ECM output is supposed to be 4000 ppm just like the speedo in the third gen. So, wasn't expecting to need to change the IP pulse divisor at all, after getting the road speed constant correct for the ECM. ???


The speedo "appears" to work correctly. Goes to zero when you stop and rises gradually as you speed up.

hotrodf1

Did more searching and came across this post:


This was a response back from TunerCat (but I'm using TunerProRT 5.0)

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
--------------------


So apparently I can't just adjust up or down and get there. I actually will need to know what to set it to.


I think the '93 transmissions had a different pulse reluctor wheel inside the trans than the 94-97s. At least I have some numbers I can try lol

EDIT: 93 only has a 11 tooth reluctor, and 94-97 have the 17 tooth.

hotrodf1

Update: using the 128 value (is a 6 from above) has me within 3 MPH of dead on.

Also slightly changed the road constant, so now the ECM speed and GPS speed match pretty darn close. See a 1 mph diff. every once in a while.

There doesn't seem to be a value for 5 for the IP pulse divisor, so I guess i'm at the end? Would be nice if there was more than just integers available to tune this parameter. Any thoughts out there? I'd like to get it closer.

Jaysz28

iTrader: (30)

I've never got any of my T56 swaps to be dead on, so I would consider 1-3 mph to be pretty good honestly.

You are working with dated technology. If you were using a flashable OBD1 PCM, you could fix it by adjusting tire size, scaling, etc.

Thirdgen89GTA

iTrader: (5)

You can use the dakota digital box to get close, then use the up/down value on the box to fine tune it. I had one for a bit, but ultimately didn't care and sold the box when the car was down for a while.