I'm going to a transmission without provisions for a VSS sensor. Although I could install a VSS sensor with some fab work, I'd like to know what I'd be giving up if I had no VSS signal to the PCM. I run strictly an open loop program, so I don't think there would be much of an impact. Off hand, the only thing I can think of is the IAC throttle follower and maybe some of the fan controls ... Any other potential problems with no VSS signal for an open loop setup?

 

I don't know about staying in open loop but when I did my t56 conversion I didn't have the VSS hooked up at first on my 93. The car would stall out everyonce in a while. When I was figuring out what was causing it I found that the ECM uses the speed for fuel tables. I hope this helps some
Jason

 

AFAIK, the PCM does not manipulate the fuel or spark tables proportionate to speed. What probably caused the car to die is the IAC was not open far enough. As stated, the PCM uses the speed to calculate how much more the iac needs to be open to keep the car running. You should be able to play with the baseline IAC positions to get the car to be OK.

Ryan

 

I've had alot of problems with cars when people loose a VSS signal. I would reccommend getting it back together or realize it will just take more to tune to an acceptable level.

 

Thanks for the replies ... sounds like it wouldn't be completely hopeless to run without it, but I'll start thinking of a good way to get the VSS hooked back up.

 

If you are running a trans with the old style mechanical setup, there is a box that screws on to that which will give you a VSS signal. Only thing to do then is you may have to go in and change the pulses per revolution in your tuning program.

Ryan

 

That would definitely help - do you know who makes it?

 

I think Dakota Digital has one. You can also get one from an 88 or so Suburban. It used this box to give the cruise the signal it needed but kept the speedo drive for the mechanical speedo. Second is cheaper. You can also probably just adapt the stock VSS to the trans you are using.

Ryan