FarmTruc

iTrader: (5)

I've been tuning this '02 RC Silv 4.8L/auto with cam and some head work and it has a very weird problem i've never encountered.

The engine has strong pushrods, pistons, springs and a healthy cam and very little head work, 3K stall, 4.10's I did all the normal pcm work, shifting, TM, rpm's, line pressure at wot , blah blah blah etc.

I have the trans shifting at 6500rpms (the engine loves it and pulls hard all the way up to it). On the street, the truck runs fast, pulls hard thru each gear 1,2,3 and shifts just fine. This is with street tires or slicks on the street.
We take it to the track with slicks on , he burns out, stages, and launches, the truck launches hard and right away just after launching shifts into 2nd gear, you can see this kills his 1/4 mile times. This happens whether you put it in 1st or Drive, it will automatically shift into second, but only on the track.
We put the stock tune in and everything is fine, i can change just one thing with edit (i disabled cot) and the damn truck does the same thing, We loaded his HPP in it and it doesn't do it, but as soon as i edit it, the truck short shifts into second on the track. This happens whether i edit the hpp tune or the stock file
Does this make any sense?
Just for the hell of it, we put my z28 pcm in his truck, and problem solved, is there some sort of mechanical device or pcm setting that is making it shift like that? If there is in the pcm, ls1edit doesn't see it. If it's mech. it's new to me.
The only diff. on the street is the tires spin a little bit. Would that make that much difference?

If anybody has experienced this please respond, this is a weird one, btw, i've never had this happen on any other truck, all engine sizes, but this one.

thanks,

allen

NoGo

iTrader: (2)

Hmm, that's odd.

Just for kicks, try and disable the ABS, TCS, or whatever it is on the vehicle temporarily (just unplug an ABS sensor and that should do it) and see if the signal is coming from one of those systems.
Worth a try......

FarmTruc

iTrader: (5)

thanks NoGo, i'll give that a try, i'll try anything to figure this one out,

ttt

FarmTruc

iTrader: (5)

nogo on that idea, anybody else, if i'm having this problem , someone will too, anybody?

thanks,

allen

H82BBad

mine does it also.

jimmyblue

iTrader: (11)

I've stepped into this, it seems, after doing some
transmission shiftpoint programming; every once
in a while I get "hung up" with a low power output
that I have to let up on the gas, to get out of.
I wonder if it's one of the transmission "abuse"
things getting tripped?

J&JsTA

I hate to ask a dumb question, but with what you have said above .. are all the trans tables in the altered file correct .... almost sounds like something is different between the stock tune and the altered tune NO?? How would disabling COT make the trans short shift, and you say this happens if you only alter COT in the stock file

H82BBad

btw when I say mine does it also I mean the short shifting part at the track. I am also having a problem where it shifts out 1st into 2nd and then to third in less than 10 feet. and under 10 mph. I am going balder trying to figure it out.

jimmyblue

iTrader: (11)

That last bit sounds like what's originally set up in
the stock shift tables, for low TPS. But it should not
be going on like that, at WOT. Wonder if you have
an intermittent TPS fault that drops the reading back
to 0%?