I have a 93 Z28 automatic and I have been having a few problems out of it. I'm currently getting prepared to dig in and install a new optispark. Well besides that I noticed that it won't go over 90mph. Its really strange when you punch it, it runs damn good up until 90mph. Then it just runs like I have the cruise control set at 90 even though the pedal is floored. The engine isn't bogged down or anything, its just like i'm cruising or it has a govenor. As far as I know it has the 4L60E transmission. Would needing a new optispark have anything to do with this? I know the computer controls the transmission shift points and what not but, does anything component wise go wrong that may cause this? My dad is getting ready to put a muncie 4-speed in his 68 Z28 and he has a built 400 turbo tranny. If its possible I will just throw that in my car instead of having to buy a new tranny. Any suggestions are greatly appreciated

 

i would see if theres a programmer for it, maybe theres a rev limiter. if not something is wrong. my friend hits 150 mph in his every other day.

 

Yeah I know. Actually now that I think about it the kid that owned it before me put a J.E.T. chip in it. I replaced it with the stock chip thinking that it may have been causing my engine flutter problems. I don't think it was until after the chip replacement that it started doing this. The J.E.T. chips will control the shift points right? Once you install one does it make that the new standard for the computer even if you reinstall the original chip? I guess what i'm asking is, is the computer still trying to compensate for the jet chip? I still have the chip so I might put it back in and see if it does the same thing.

 

Your car actually has the 4L60 transmission, it isn't the electric version like all other 4th gens, '93 was kinda the oddball of the 4th gens, but that's typical for the first year of a new body/motor etc. It's possible that it's governed, but not likely since they were governed at 108, not 90. Maybe your change back to the stock memcal chip is causing issues, pop the J.E.T. chip back in and see if it helps.

 

95slvrz28 is absolutely correct. Your car used the 4l60 transmission which is just a different name for the old 700R4. The only thing that the computer controls is the application of the torque converter clutch (TCC). Make sure the transmission is not hanging in third gear? What RPM are you turning at 90 MPH?