Heya, not very familar with PROM so I'm hoping someone here would have some quick input!

Just bought a 91 Z28 305. The car was originally a manual but the previous owner put in an Automatic 700R4 trans 6 months ago. I've heard that the PROM needs to be swapped to match an Auto and i don't think it was done (where could i look up the part # to find out?) What will the wrong PROM in the car cause? The car runs great except for the following which i think could possibly be related to the PROM:

1. trans shifts to 2nd when idling at around 5mph (all other shifting normal, OD functioning, it's just irritating)
2. Idle speed to high (about 800rpm in drive)
3. Spedometer not working (new automatic VSS was installed which is working properly). Spedometer reads about 120 mph when moving about 5mph and then pegs to the top at anything faster.

thanks for your replies!!!

 

What is the code on your MemCal?

 

AWFZ
5504

1P0115

 

hey, im about to do a swap similar to this im putting an 1987 700r4 in a 84 TA that was 5spd. but i may not do this if i have to swap computers and go through all that (theres a T-5 sitting in my garage but i would have to rebuild it or get it rebuilt) so do you need a different computer for this swap, for the lockup torque converter or whatnot.

 

It's a LOT easier than the other way around. I'm not sure about the 84 TA so check the dealer, but the 91Z had identical computers for both 5spd and auto, the only difference was the PROM chip that plugged into it. That said, I did run the car for several months with the factory 5spd chip still in it with the 700r4 and had no drivability problems. Also, in the cars with factory 700r4 (in 1991 at least) there was wiring to the trans for shifting, the trans put in my car was set to shift itself and had the OD locked in the top gear (I think the lock-up is the only thing that needed to be configured here). So in my case there is no wiring from the car to the 700r4 whatsoever; runs fine this way. When I forked out the cash for the auto chip it lowered the idle appropriately so that it wouldn't slam into drive or reverse.

Note that you need to have the speedo set correctly before putting in the auto chip; (in '91 at least) it apparently adjusts the air/fuel mixture or spark according to velocity. Found that out pretty quickly when the car would die everytime I tried to drive past 2mph since I didn't have the right speedo sensor in

Lastly, the rear trans mount for the torque arm on a 5spd will work with the 700r4 but is significantly weaker. I drove with mine for 2 years till it broke slamming the torque arm to the ground... had to swap it out on the side of the road with a unit from an auto trans car. even swap, have had no problems since.

Hope this helps!

 

how much did that chip run ya? and one quick question mabe you could help me answer. would it be cheaper, or worth the extra money, to rebuild a t-5 and put it back in??

your reply was very helpful

Joe

 

I think it was about $85 from the dealer

If you have a 700r4 in good condition ready to go yes it would be cheaper to swap it. Otherwise i would assume it's about equal cost to rebuild either. Personally, given the choice I would never want to convert to auto on a car like this; it will be faster and ultimately funner to drive as a 5spd. The downside to 5spd of course if you live in LA like me with tons of traffic to contend with!

 

thanks