I have an 88 chevy truck with a 95 trans am lt1 (obd1) with a 97 4l60e. Truck has been on the street and strip for years with no problems on street tires. Bought M/T radials and now tranny won't shift 1-2. Burnout, stage, launch, get to the top of first and it bounces off the limiter twice and shifts to third. It stays in third even when i stop and take off from the time slip booth. My tuner thinks it is going into failsafe(limp) mode, but we can not get the scanner to read to verify. Just had the trans gone through and swapped converters. Everything looked fine to my trans guy. Replaced vss still doing it. Put street tires or skip the burnout with the M/Ts on it and beat the crap out of it and it performs flawlessly. I'm at a loss and pulling my hair out. Been chasing this for at least 3 months. Any suggestions would be much appreciated. thanks

 

WTF never heard of that. I'm wondering if it may be a overheating prob do you have a cooler? Also see you have a 97 4l60e from what I have heard 94 and 95 have different set up on solenoids in the valvebody. IM this guy he knows his ****
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I'm hoping he or someone like him sees this post and has the cure all! I,m headed to San Antonio next week end for a GM truck playday. If I can get this fixed I think I can dip into the 12s.

 

I think the first thing you need to do is be able to see what the computer is seeing or throwing for codes. This will help in your diagnosis. Being that your vehicle is a hybrid a stand alone trans computer would be a good idea. Vince

 

Are they a different size tire? Like taller or shorter? The trans uses mph to make the shift, if you have a different size it may be screwing that up.

 

Sounds like "stall wall" get a hold of Bryan at pcm4less he has a fix for it..

 

Street tires are 295/50/15(26.5" tall)
M/Ts are 275/50/15(26"tall)
They are close. I thought the same thing, so I had my tuner lower my shift point 1-2. When I ran the M/Ts with no burnout(of course it spun off the line) it shifted 1-2 at the same rpm as the street tires. I think the computer and speedo only sees the tailshaft speed and rpm. Tire size is only relavent in determining accurate speedo. At least that is what I am thinking ,but I could be wrong. Shift 1-2 is at 40mph, 2-3 is at 75mph. Gears are 3.42 with detroit locker.

 

I'll try to call Bryan today. What is stall wall? My first converter was a factory restall 2200. My new converter is a PT 3200 Yank. Did the same thing with both converters.

 

Stall wall is when the inputshaft and tailshafts speed are diffrent(from having a loose stall) making it go to limp mode

 

Stall wall is when the inputshaft and tailshafts speed are diffrent(from having a loose stall) making it go to limp mode

 

I believe its your tire sizes. My dads vette did the same thing. A half an inch makes a difference. Its all in the computer programming. If you don't have a laptop, your out of luck between switching them back and forth. Your tuner should know that.

 

If the tires are different diameter that would be the equivalent of a gear ratio change and would affect shift points. You would need to be able to change the tune for each set up. If this is the case and you dont have a tuning software of some sort, You could consider getting a second PCM thats tuned for the tires and swap them out when using them

 

When this problem first started the difference in tire size was the first thing I thought of. I went to my tuner and he lowered my 1-2 shift from 45mph to 40mph. Didn't help. I just drove it with the M/T on the street for the first time a few minutes a go. I did a burn out just like I do at the track. Stalled it up and launched(they hooked up better than I thought they would) it shifted 1-2 perfect 3 out of 5 times. Twice after the burn out it stayed in second gear. I turned it off and waited a few seconds, started and it was fine. At the track it is more like 1 out of 20 passes, but every now and then it will shift correctly. If it is tire size I think it would not shift right at all in any gear. Maybe I should just do my burnout kill the truck for a few minutes start it up and make a pass. I doubt the track and other racers would go for that.
One more thing...I have an OBD1 and I don't think it reads input shaft versus output shaft for stall wall.

 

I would be checking your pump.
Either that or the rest of the unit is on its way out.
If you had 2 different converters with the same problem, and a VERY confident that the tuner has you straight, you will have to look at the trans. At the very least drop the pan, and look for evidence of damage.

 

Now what does it do with the stock tires on? Same thing? You might of touched on that above.

 

Mine was doing the same thing, trust me call pcm4less they will fix it. obd1's are bad about stall wall.

 

Just an update. It was stall wall. Bryan fixed me up. Shifts perfect. Thanks for all the help guys. I appreciate it.