Making too much power, unable to shift from 1 - 2 under WOT
 

Hey guys,

So I recently upped the boost to 18 - 19 psi, installed PRC stage 1 LS6 heads, custom grind cam, 8-rib pulley setup with 10% overdrive crank pulley, and a hefty dose of methanol. However me and my tuner are facing problems getting the car to shift out the 1st gear under WOT. I know its something in the tune but we can't get it to work. Rev limiter is at 6500, we even set the shift command at 5500 RPM, it worked the first two times and then it went back to not shifting. I flushed out the transmission and checked the pan and fluid. Everything is well and in place. If anyone faced these problems or knows something we might have missed while tuning please chime in!

Greatly appreciated.

What kind of trans? Is it built or any aftermarket parts in it?

I'm experiencing the same problem with my 4L80e and can't find a solution. GMCtrk also has this issue and he says its a pcm issue. He has logged all the trans parameters and said the pcm doesn't command the shift fast enough even if he has it commanded at 4500rpm.

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6L80e. It definitely is something in the tune that needs to be fixed. Can't seem to figure it out though!

can you go back to a previous tune that worked? just to make sure its in the tune. Are you logging fuel pressure? does it pull hard to the rev limiter and not shift? or does it not shift because it noses over at the top end? I'm not up on the newer trans/pcm's but I've heard on the older stuff you can't just change the rpm's, you also have to have the mph be close to the rpm you want it to shift at. You can't command 2nd gear at 25mph and 6800 rpm and have it shift at 6800, the two need to be relatively close to accurate for the rpm/mph. hope that makes sense.

Yeah, it pulls hard all the way to the rev limiter and keeps revving. I tried this on D and Manual also, all the same. I even set the shift at 5500, but it's back to not shifting. Also tried lowering the 1st gear shift torque, still no dice.

if you have hp tuners an have the tune file, you should post it so people can take a look. i for one am curious and would like to look at it.

sounds like your full throttle shift speed is higher then your full throttle shift rpm

also check your "hot" shift parameters, i say that because you said it shifted after you changed the tune allowing the engine/trans to cool down.

Do a scan and log trans commanded gear to see when it is commanding the shift.

^^^^ this. Make sure it isn't commanding a shift or it would be a mechanical problem.

I noticed when I went turbo I had to lower my shifts, it revs up so much quicker I just dont think it can shift fast enough.

My tuner is also in the midst of asking some of his more knowledgable buddies about it. So we'll see where it goes from there. With that said, I'm sure some fellas with heavy mods faced this problem at least once before, but they're probably too busy racing than posting online on forums lol.