mrvedit

I made a mistake in my last post. I was thinking that your trans was not shifting up at WOT; I think you mean that it is not shifting down from 4th to 3rd at WOT. I don't recall if this downshift is only related to throttle position and/or also engine load. Engine load is calculated by the PCM from the MAF and MAP signals. Engine load does change the line pressure in the trans, but it would take very messed up hydraulics for higher line pressure to prevent a downshift; shifts are mandated by the PCM controlled solenoids.
Despite my earlier mistake, I'm still confident that your trans is fine and that the PCM is not requesting a downshift because of a faulty reading from a sensor (or a faulty tune). You really need to get a good scanner hooked up (preferably a logging scanner) and an unbiased person to perhaps interpret it for you.

Black98T/A

iTrader: (5)

No you are correct it is not shifting UP at WOT. If I'm at a dead stop and floor it..it doesn't shift into 2nd...it just goes to redline. If im on the highway and floor it it downshifts a gear and goes up to redline it does not shift into gear. If I give it 3/4 throttle it downshifts and upshifts into gear. Normal driving 1-2, 2-3, 3-4 lockup etc all shift perfect.

mrvedit

OK, glad this is clear now - you are hitting the redline at WOT before the trans shifts. At 3/4 throttle it is fine.
Like I said, at WOT (and only at WOT) the PCM will not command a shift until both the tuned (programmed) speed AND rpm are hit.
There are many other threads discussing this exact same problem. Often it occurs after installing a high-stall torque converter which has more slippage and therefore less mph at redline. The solution is to change the tune and reduce the MPH upshift speed by a few mph. You are saying that your tune did not change; in that case it could be that your torque converter has gone south and is now slipping more. OR, your VSS sensor has gone south. Sure, a defective trans could cause the converter to slip or have internal slippage, but to have the same problem before and after a rebuild is less likely. (However it could happen if the rebuild did not bother to fix the notorious leaky TCC valve in the valve body.)

You mentioned that your speedometer is off. Get that fixed FIRST; try a new VSS sensor, it is only $15. If the VSS signal is off by only a few percent (like 3%), your trans will not upshift at WOT.

Black98T/A

iTrader: (5)

Trans did not shift at WOT with stock torque converter before rebuild. I just put a brand new 2600 torque converter, rebuilt trans, and had the PCM retuned. The tuner screwed the speedometer up this last tune, it was fine before and still did NOT shift at WOT.

mrvedit

Have the tuner reduce the WOT upshift speeds by 5% or more. I purposely set mine 10% lower than you might expect so that the upshift is controlled only the selected (tuned) RPM. That way I can quickly change my shift points at the track without having to think about MPH.
Or spend the $600 to get a copy of HP Tuners or EFI Live and do the tuning yourself. Personally I really enjoy the tuning process.
Good luck; I don't think I have the experience to help you any further than this.

Black98T/A

iTrader: (5)

The tuner already reduced the upshift speeds, I just got off the phone with him and told him the trans downshifts and upshifts at 3/4 throttle and he's now telling me it's not the PCM but the trans. Basically almost everyone is telling meit's the trans except the builder who said the computer isn't commanding the upshift and he's 100% positive it's not the trans.

mrvedit

Without seeing scanner data and the actual tune file, I cannot help you further, and by the lack of other replies, I suspect no one else can either. You need real data and a competent and trustworthy mechanic/tuner to solve this.

Gilbert@Ace Racing

After reading this thread I would suggest that you have a competent Tuner address this issue for you.

What shop did the Tuning?

g

Black98T/A

iTrader: (5)

PCM for less

Black98T/A

iTrader: (5)

so I had a third party take my car for a ride with me and the computer is not commanding the shift at WOT. Im going to try another pcm.

mrvedit

Sorry, but I'll bet you $5 that it is not the PCM and that it is either the tune or a sensor. Most likely the tune.
If I am wrong, PM me your address and I will send you a $5 bill.
In any case I hope you get it fixed soon.

ninetyeightbird

Im having the same problem transmission shifts fine at part throttle but wot just bounces rev limiter. I installed an lq4, cam, lt, and a tci 3500 converter, about 3 weeks ago car shifted fine at wot after the install but yesterday quit after I hit 130mph in a race. I thought I trashed the trans but checked the fluid and it wasn't burnt. I know I still need a tune but figured If it was the tune it wouldn't have shifted right from the get go

mrvedit

There are many posts here about people having the EXACT same problem after installing a high-stall converter, and 99% of the time a tune fixes it.
You are probably "right at the edge" and a different fluid level or temperature might be causing you to hit the rev limiter just before it wants to shift. Get it tuned and you will most likely be fine.
Keep us posted.

ScottyBG

I agree with Mrvedit, without datalogging the car I can't say for sure, but based upon my tuning experience, about a 95% chance its in the tune would be my guestimate.

All PCM's do not operate exactly the same. Why, I don't know? I have had a '98 pcm that didn't give a damn about what I put for RPM into it, it always shifted at the MPH in the tune. The conventinal logic says both the RPM and MPH need to be met to command a shift. I have also heard of trans not shifting properly if the MPH and RPM are set too far apart, like setting all the MPH to 0, so only the RPM is used to shift. Others have said this works fine? If the tranny is shifting correctly at all but WOT it is very doubtful it is the tranny. I also agree with Gilbert, go to somone that knows how to tune? I noticed you said PCM for less tuned it? Was it a mailorder tune? If they don't actually have the car to drive and datalog, and know what they are doing, that makes it much more difficult.

I don't know if you have been in there, but there are 2 places to set the WOT shift MPH and RPM, the 100% TPS in the main shift table and there is a WOT table. To me is seems redundant to have both. If they are not both set the same and correctly you will have problems. I first set the WOT Table to what I want, then populate the 100% TPS column, then blend in the 95%, 90%, 85% back to smooth the curve.

If you can have somone with HP Tuners pull the tune out, the .hpt file, I'm sure some people can take a look at the tune for you. If you want to PM me with it, I would look at it for you.

Black98T/A

iTrader: (5)

Did you read my post(1) where I said It shifted at WOT for 2 years with a pcmforless tune then all of a sudden didn't? How is a tune going to retune itself from shifting? I could understand if it didn't shift at WOT right after I had a tune but that's not what happened. I just bought a used stock 98 Z28 PCM off here for $123(shipped and western union) and I'm going to plug it in and drive before I send it back to pcmforless to get tuned, if it shifts at WOT I could use that $5 towards it..

Black98T/A

iTrader: (5)

Your problem might be the converter..which is what several people told me even though I only have a 2800 stall except it wouldn't shift at WOT before I installed the converter.

Black98T/A

iTrader: (5)

Ok got the PCM today and still no WOT UPSHIFT!

So either this pcm is having the same problem which I doubt or something else is making the computer not command the upshift at WOT????

mrvedit..please explain if you can .how can this still be a tuning problem?

transam19

iTrader: (1)

Its a tune issue. Just seriously talk to a real tuner and have them look at ur file. We are all trying to help you out since most of us have been thru the same problems. Never put anyones opinions to the side. Never hurts to try something that will probably help you.

Black98T/A

iTrader: (5)

If its a tune issue why is it not shifting at WOT with this untuned PCM from a 98 Z28?

transam19

iTrader: (1)

U can't just POP a new pcm and expect it to work there is still adjustments that need to be done in order to meet for the trans to shift properly. Every tune is diff and will need to be adjustd. Try getting in touch wit a reputable tuner and have them look at ur tune.