Still working on Project '99 SS, when we bought the car it had a blown 3.23
axle, we got a 2.73 axle from a 2000 Z28. That threw off the speedo and all
the shift points. We got the speedo fixed but the trans still shifts all weird. I
am hearing its the "shift tables" that need to be updated. The guy we got the
2.73 axle from had his laptop crash and lost the original tune. I was wondering
if anyone had a Bin file with a stock tune for a 2.73 LS1 equiped car. This will get
us a starting point. The guy helping us has a tune for a '94 Z28, but thats an LT1
car and I wonder if the shift points would be the same.

Another issue we are having is the car does NOT respond to manual shifts. If you
are in 1st gear and do a take off (regardless how agressive) when you shift to
2nd gear it does nothing until you let off the gas and then it upshifts. The trans
was rebuilt shortly before we bought the car, though I dont know the quality of
the shop that did the work - they list a V6 converter? Also, under WOT it will
bounce off the rev limiter BEFORE it shifts, basically shifting when you left off.

Ideas?

Tom

 

Get it reprogrammed to fit what is actually in the car. Your car goes off of mph tps and under certain conditions rpms. You need to retune a whole list of tables to make it work, or just find somebody on ls1tech or here with a stock ls1 file and 2.73 gears.

Your car will not respond to manual shifts under wot or otherwise really unless certain conditions are met, you can modify the tables but that is the stock behaviour to keep idiots from tearing things up.

It probably bangs the limiter because either A the trans is too slow for how the wot shift tables are set up or B the mph thresholds for the tables are incorrect now with the new rear gears.

 

For my LT1 RPM and MPH thresholds must be met to upshift.

 

These conditions must be met even for a manual upshift? I think two things
may have been mixed here. I doesnt do an immediate upshift when manually
upshifted, and separately, it will hit the rev limiter instead of upshifting on a
WOT run. Do your responses mean that you feel its programming and not a
mechanical problem with the trans?

I am looking for a stock tune for a LS1/4L60E with 2.73 gears, as I mentioned
in my first post. Thats what we are attempting to do, to reprogram it with a
tune that fits thats actually IN the car : 2.73 ratio axle, rather than the 3.23
that was original. I hope that is more clear.

Thanks again

Tom

 

It is a programming issue, i am bout 90% certain.

The trans will ignore whatever you think you're doing with the gear selector when its at wot or even part throttle its programmed to allow you to manually shift very conservatively so you dont do anything silly like go from od to 1 at 70mph and give gm grief if it was under warranty.

Correcting the speedo problem isnt going to fix anything since all the tables must be adjusted accordingly also.

See the sticky at the top of the forum for a long long explanation about how the trans tables for an lt1 pcm can be adjusted. The function of the ls1 trans tables will be close if not exactly the same as the lt1 tables.

 

When you changed the axle ratio, but did not change the tuning, it shifted at exactly the same rpm as before the axle change.

Since it shifted wrong, you know that either it already had a bad program in it, or you have a hardware problem.

Once you changed the speedometer but not the shift tables, with the change from 3.23 to 2.73, the car should be short-shifting.

So, again, either it had a bad program in it before, or it's a hardware problem.

 

I knew about the downshifting safe guards, but I did not think that manual
upshifts would be effected as well. Thats good to know.

Tom