Tonight it the first time it hasn't rained since I got my car, so I did a little testing tonight, came back disappointed, need some guesses/knowledge.

The facts:
93 z28, 4AT, low milage, probably due for a full tuneup, chip of somekind, unkown brand/effects.

the problem: right around 4800/4900 and up until shift/redline, the car/tranny/engine seems like it is hesitating to shift, as if it doesn't know what to do when it hits redline/WOT (because one wont hit redline if not at WOT in an auto, i think...) and it makes a not-so-good sound, hard to describe, as if something is slipping/missing. the bad sound is not coming from the rear of the car at all, defintely coming from the front of the car, certainly not the rear/diff. area.

now, give it just less than WOT, say 3/4's, and she runs strong as hell, up to around 4500 or so before she shifts.

heres the kicker...

from a stop, WOT, with car "manualy" in 1st then shift to second, same hesitation. however, from a stop, in first, half throttle up to redline then shift to 2nd, all is peachy keen, perfectly smooth shift.

now, i just purchased the car, and while it wasnt sitting for a long time, it was probably only driven once a week or so for the past few months.

I figure it is just in need of a tuneup, complete, everything. change tranny fluid/filter, possibly the fuel fliter, maybe she's having trouble with fuel delivery at WOT.

cheked the trans fluid level, it seems to be too full, according to a more mechnicaly knowledgable friend of mine, who's owned a few 350s.

is this a common problem in the AT I am running (all stock except for the chip). could this be the chip? anybody think it could be the engine? tuneup?
she sounds like she could use a tuneup, but no smoke or other such problem with engine.

Anybody have any kind of insight? need more info? guesses? Please help out a little, I would appreciate it.

(posting on drivetrain forum as well)

-Thor K.


PS- car is perfect other than at WOT, like I said, at or around the redline when hesitation begins... hopefuly just needs a tuneup :-/

 

so, the more i think about it, the more i am thinking the engine is in need of a tuneup.

the hesitating sound came from the engine bay, and while yes, it hesitated to shift right away, i think it was more the engine and not the tranny having problems dealing with the higher rpm range.

 

I have a Jet 2 module and notice the same thing. Last night my trans seemed to slip when it was cold, i mean just started up and floored it but thats my own stupidiy. My shifts go into the redline then shift, but my trans rarely slips. I only have 66k miles on my car a few minor mods, but just as you said if i shift from say 2nd at 50mph at part throttle to 3rd it delays shifting. Doesnt slip, slams it into gear but it still delays.

 

Yep, wow, almost the exact same thing as what happened to me. Yeah, it was a little cold yesterday, but the only difference is, mine is fine doing anything except WOT; shifts like a champ at 3/4 throttle around 4500, but dare creep near 5000 and she's hesitating like hell to shift, with the nasty noise coming, seemingly, from the engine bay...

I am not sure what kind of chip mine has, is there any way for me to check?

Thanks

-Thor K.

 

I actually don't know where the 93 chip is. With my module, it's plugged directly into the PCM under the hood. Sounds like your transmission may be going out, or your chip could just be malfunctioning. Find it an remove it. I heard it's under the dash by the OBD1 connector.

 

While I can't imagine the tranny going out at 64k miles, I knew the owner, handicap tags, im sure he opened it up occasinaly, but not regularly.

But again, I am not even going to pretend like I know anything technicaly about these cars, so you may be right.

Yes, I need to find out what kind of chip I have, that's for sure, having some trouble locating it/the ecu though.

Thanks again for the help.

 

On the passenger side between the wheel well and windsheild is the ECU/PCM. Its a silver/black box.

 

awesome, thanks, goin out to check it out.

 

I think I fig'd it out. I don't believe it is a transmission problem at all.

It does this same hesitation when, say, I am cruising along at 40mph or so in 4th gear, and give er about 1/4 throttle or 1/2 throttle, it'll do the same hesitation as at WOT, just on a lesser scale.

I'm thiking basic tuneup/fluids. I'll just not drive it at WOT until then.

 

Well i repalced my trans filter and fluid. Didnt seemed to help a little. Mine rarely does it and only when its extremely cold. I think yours might be your chip though.

 

Well, dont think its the chip, especialy if it is a tranny problem, my ecu doesn't control the tranny, have the (edit) THM 700 R4 .

Yeah, it's been hella cold the last two days, this may have something to do with it, and tranny fluid is definitely over full.

Again, I will do complete tune-up, flush and fill (porper ammount) tranny fluid/filter, the whole deal. After that, we'll see.

Again, i really don't think it is the tranny at all, sound is coming from engine bay, and she acts like the fuel doesn't come as easy above 4500/at WOT.

But, I may be entirely wrong. One step at a time I guess.

 

May want to check the opti if its only happening at wot. Could be going bad, just a thought.