what gear ratio is my pcm tuned for?

[jleasure]

First off I have a 96 bird m5 3.8l. A long while back I bought a 97 pcm from a guy off this site who claimed that it was out of a 97 m5 and was tuned for 3.42 gear ratio and had no speed limiter. Well, my 96 pcm crapped on me and I was forced to throw in the 97. I thought that since my gear ratio (3.23) was less than the pcm's gear ratio (3.42) that the speedometer would show a slower speed than I was actually going. However, it turns out that my speedometer is actually showing a higher speed than I am actually going (showed about 56 when I was actually going about 52). So, this makes me think that the gear ratio tuned in the pcm is actually lower than the 3.23 that I have in the rearend. But this doesn't make since since the 3.08's came out of automatic cars.

Is it possible for a 97 pcm out of an auto to work in a 96 manual by just straight plug and go?

Is there any way I can check the pcm to see what gears it is tuned for? I dont know how to do this.

Any help is appreciated. Thanks guys.

[ssms5411]

Re: what gear ratio is my pcm tuned for?

A4 pcm will not work in a manual , it will throw codes , tried that once.LOL Plus the PCm files on the A4's are different than the M5 as in timing and such, plus the transmission cods its going to throw. 3.42's are actually lower gears than 3.23's. I have had 3.23's,3.42's and now 3.73's. Only way to check the PCM is with Hptuners , to make the A4 PCM to work with your M5 you need a 97' M5 Vin # to flash the 97 PCM at a dealer or if someone with Hptuners they can reflash the 97 PCM to a M5 file.

[97rs4life]

Re: what gear ratio is my pcm tuned for?

yea a write entire with a m5 file and hptuners will work

[jleasure]

Re: what gear ratio is my pcm tuned for?

Well the 97 pcm is in there now, and the only code i'm getting is p0441 which is due to incorrect purge flow or something (gotta figure that one out when i get the time), so the pcm must be tuned for m5. The thing I dont understand is why I am going slower than my speedo says, doesn't that mean the gear ratio # in the pcm is lower than what I have (3.23). That means the gears must be higher (lower gear ratio #) which makes either 3.08 or 2.73 possible, both of which were only available in automatics. Am I wrong??? The only thing I can think of is that the 97 pcm used to be tuned for an automatic then switched to m5 before I bought it, without changing the gear ratio along with it. Idk who would do this lol, and I don't really know why someone with an m5 would want higher gears (lower gear ratio #) in their car unless of course they drove a ton of highway. Is there any other software besides hptuners that I can download (free preferably) to my laptop where I can see what gear ratio my pcm is actually tuned for. I have the laptop-to-obd2 connector, just need the software.

[jleasure]

Re: what gear ratio is my pcm tuned for?

anyone?

[ssms5411]

Re: what gear ratio is my pcm tuned for?

Buy Hptuners and read the PCM? Or buy a PCM from PCM for less with your mods and have them ship a PCM. There are no free programs to read PCMS if there were all the tunning companies would be out of buisness. Why not look at a RPM and gear calculator and see what the RPM is in that gear and then look on the chart to see what gears its tuned for. Just calculate your tire height and if you know what gears you currently have then it should be pretty easy. If the PCM is tuned for another gear than what you have then its going to mess the speedo up, if you have a auto then it will mess the shift points up and most likely ruin the trans. Swap your old 96' PCM back in if your not going to buy Hptuners for the 97' PCM, before you blow something up , that would be my suggestion.