Appreciate any insight on this problem.

I have a 1997 limited edition 30th Anniversary Z/28 (the white with the orange stripes model). It has 18,500 miles on it. I bought it brand new and as you can guess I drive it only rarely. Anyway, I was driving it3 weeks ago on a perfect Saurday and it started shifting hard (very hard 1st-2nd) and the "Check Engine" light came on. I was near my Chevy Dealer and went into get the code(s) read. The OBD-II scanner threw up 2 codes, both having to do with the Shift Solenoids.He cleared them and I didn't even get out of the Chevy dealers lot and the "Check Engine" light was back on.I took it in the following Monday to the dealer and they changed out all the shift solenoids (3 each) and reconditioned the valve body. Put it back together and did a test drive. It shifted OK for just a minute or so and then the check engine light came on again and it was shifting hard (very hard) again. The transmission tech ( he has been doing tranny work for Chevy/Gm for over 30 years) then began to chack all the wiring and "ohmed" out the wiring harness from the PCM to the tranny and said all that is fine. They have ordered a PCM for it and are waiting for it. I left the car there for 2 weeks (they had it on a lift with the lift up at about 7 feet so no one could scratch, bang, ding the car). I went and broughtthe car home yesterday to put in the garage again and told them to call me when they get the PCM in. The car runs great just shifts real hard 1-2 and hard in the rest of the shifts. I understand they have a "SPARC" case I believe to get a PCM from Chevy/GM. My questionsare this:

1. Can it take awhile to get a PCM for a 97 Z/28
2. Do you agree that the PCM is probably the fault

Thanks...

 

It's practically impossible to say how long it would take to get that PCM, depends on a lot of things. but as for the PCM being the problem, I wouldn't think so but if a guy who has been working on them for 30 years says thats the problem I wouldn't doubt him. Do you have old nasty fuild in your trans? 4L60E right?

 

The car only has 18,500 miles and the fluid and filter has been changed when he changed the shift solenoids. The fluid was still good as new when he changed the solenoids. I am pretty sure the solenoids didn't need changed, but they had to do it to eliminate that as the problem. They didn't charge me forchange them since that didn't fix the problem.

 

Shift solenoids do not affect shift quality, they either work or not work.
Possible causes:
1) Throttle position sensor
2) Fluid pressure switch
3) Pressure control solenoid
4) Pressure switch
5) Transmission temp sensor
6) Engine temp sensor.
7 VSS

 

TPs I think is unlikley since he would have a lot more problems than his trans shifting hard (like not being able to go under 160MPH). If it were engine temp (that effects trans shifting?) his gauge would have to show it or not work. if it's a trans temp sensor I wouldn't think that that would make it shift hard.

Does it always do it now? even the first time you start it up and shift from 1st to 2nd? or does it have to get warmed up? is it the same thing that happened after they thought they fixed it the first time? as in, did they put something new in and in broke again in just a couple of minutes?

 

I have a 94z28 exact same problem. I put in a new pcm and it fixed the problem so Id say yes that will fix it.

 

The problem is immediate. No warm up time is required. The first time it shifts after pull ing out of the garage will be hard and all of them are hard, but of course the 1-2 shift is the one most felt.

The problem happened immediatly after they changed the solenoids. No time for them to break, it was immediate hard sfifting. So after seeing what rassilon said it appears it probably is the PCM causing the hard shifts, the PCM is basically "lying to itself" is how theyput it. it thinks things are happening that aren't. None of the other items z28pete mentioned show up as throwing any codes in the PCM either.

 

Well, they have the proper diagnostic tools, and they should be able to fix the problem.

As for the TPS, the PCM uses the data from the TPS to control shift quality according to throttle opening, similar to the old TV cable arrangement. Same with the engine temp, ETC,but to a lesser extent. Also the ETC and the temp gage use two different sensors, so the ETC could be transmitting false temp to the PCM when the coolant temp is actually OK.

Of course, if the PCM is crazy, none of this stuff applies. The dealers have the tools to run diagnostics on the PCM itself, and that is probably why they want to change it. Much easier than taking the tranny apart and find out there is nothing wrong with it. LOL

 

BTW, here is a couple pics from this year...

 

Ok, the problem has been solved by a new PCM.

Took a **** case to get a new PCM for it but it finally arrived, got programmed and installed and the shift problem is fixed.

Thanks for all the help and suggestions.