RevGTO

iTrader: (12)

Since the problems are not consistent and wet weather seems to have an influence, I would inspect the PCM harness for corrosion and make sure everything is connecting properly. If that is all okay, the PCM itself could be the source of the problem, generating erratic performance.

It's tough sometimes to distinguish on the basis of anecdotal reports whether a genuine problem is being experienced, or a person simply does not like the performance of a vehicle that is operating normally. The latter was my case with the stock automatic tune.

bammax

I came across a tsb from way back that sounds similar to what you're dealing with.

tsb #010730036

SUMMARY:SERVICE ENGINE SOON LAMP ILLUMINATED, INCORRECT TRANSMISSION SHIFTS, POOR PERFORMANCE OF ENGINE, TRANSMISSION SLIPPING. *YH

I can't find the specifics on the exact issue since it's a tsb from 2001. You can ask a gm dealer to look it up though.

Saudrack

I see no Service Engine Soon lamp, but that's interesting. I look if I can find out something about this.

Now I have another workshop found, this guy makes a lot Corvettes and other US cars and is the first who really seems to want to fix it. He has Tech2, HP Tuner and all he needs for this cars, checked all the electrical signals up to the O2 sensors, and says there is no issue, all works absolutely how it should. He said the PCM commands at about 3/4 throttle the kickdown-downshift, but it's absolutely sick to do this at 40 mph into 1st or at 90 mph into 2nd gear... He isn't sure if it can be that the shift table was changed by someone earlier and the software update did not put it back to factory settings. Does someone know if that's possible?

He drove my car for about 130 mls in different weather, noticed the car shifts very late and often hesitantly, shifts harsh, but he never noticed the hard gear slamming, vibration in 3rd, the fluctuations or the hypersensitive downshifting. It's not always reproducable on demand, the car does it or not... He is also confused from the TCC how it works, locking under load and not unlocking in 4th gear... That's total crappy but if it's just a tuning thing, he will do it for me.

He supposes a transmission internal problem, thinks the mentioned rpm fluctuations and/or engine choke-down at about 2500 rpm and also the feeling of too little torque and differences in engine performence could be caused by the converter. He also thinks some clutches could be worn. Oil looks still like new, but he reminded me I don't know how old the old transmission oil was before I let it flush. That's true, it could be that the previous owner put in new oil right before he sold the car to me, I don't know it, he said not, but was he honest?

I did the stall speed test, how I could find it should be 1800 rpm, right? Mine did 1900 rpm, does that mean something? In the whole internet I could not find one info how much deviation is allowed. Maybe no one knows it

It's still confusing to me that the car sets no codes. I told the unplugged MAF brought no engine light and also no code. I tried same thing with the IAT-sensor and the TPS, unplugged and drove, also no engine light and no code after that, can this really be ok so in this car???
I also tried driving with unplugged EGR and only this one made my engine light going on and had set a code.

I also noticed lately that the slipping at manual shifting into (D) under load is not always. I tried it a few more times, it slipped when TC was already locked in 3rd and then going manually into 4th and it did not slip when TC was unlocked. Also the vibration, it shuddered in 3rd, went away in 4th, back in third it shuddered again, and so on, tried it a few times. So I thought it would be the TCC slipping only in 3rd because of more torque as in 4th. But on the next day I tried it again and then it also slipped with unlocked TC going manually into 4th and this time zero vibration in 3rd... It's driving me mad.
And just yesterday I rolled downhill in 4th with about 70 mph NO foot on the gas or brake pedal. So the TC was locked at the moment, but again I noticed a stange thing. For a moment it felt like the TCC unlocked and locked again. I don't know for sure but it felt like this.

And also yesterday I noticed that the full throttle shiftpoint has raised. Until yesterday the car each time shifted at 5700 rpm, at 56 mph on the speedo into 2nd and exactly at 100 mph into 3rd. Yesterday I did full acceleration in 2nd and it reached 6000 rpm and about 105 mph before it shifted into 3rd. I could not believe it. I tried it a second time and again it reached 6000 rpm. I don't understand it. How the hell can this change???


This week the mechanic is not there, I'll contact him next week again to make an appointment for the line pressure test. I have already talked to him about it.

fst100

iTrader: (5)

unplugging the MAF and any other sensor should throw the DTC light once the car doesn't sense it and runs like crap and resorting to internal saved data sets. something doesn't sound right on that part. I can't recall but have you thought about swapping PCMs yet from another 99?

Saudrack

With unplugged IAT the car ran as always, I just think there were more gear-bangs.
With unplugged MAF it felt just a little different, but not really much.
And with unplugged TPS it really runs like crap, no power, early upshift, no downshift, gear-bangs as horrible as they can be...
But no light and no codes at all.

Yes I thought of swapping another PCM but I have none and know know one who can borrow me one. I 'll ask the mechanic next time if he has a connection or an idea. Otherwise I 'd have to buy one.

bammax

It almost sounds like someone messed with the tune and either did it wrong or tuned for specific parts and then stock parts went back into the car. Sometimes people build a race car and then put the stock parts back when they sell it and if they didn't retune it to stock it causes all kinds of weird issues. Not triggering the check engine light after unplugging sensors would make me think it's something in the pcm being off.

Saudrack

I 'm sure this was never a race car It had the old stock shocks, when you see the old rusted bolts and nuts on the stock exhaust manifold and so on... No, on this car were no other performence parts. But the car once had an accident, rocker panel the most, also door and lower side panel behind and front all on left side. So the car defenitely received a hard knock once. Perhaps too much for the PCM and it's going mad?
The mechanic said all signals were fine and he didn't think it's a PCM issue. But I'm careful with the transmission issue he suggested. If it's the tranny he can also rebuild it, but if it's not and I have a "new" tranny in the end but also the same problem then I'd not be happy...

I 'm also careful with it because some rather rare times it shifts temporarily good and smooth, and again I must say it: When I notice a nice and smooth shift and step more on the gas at the same time, you can immediately feel that the torque is noticably better and the car pulls stronger. But thats also just temporarily.

I think, how can the car temporarily shift and drive really good if clutches or the TC are bad?

And the newest thing... Why changed the full throttle shiftpoint? What controls it? I think it's the shift table in the pcm, or not? How can it change by itself?

It's all so curious... also that it sets no codes without the mentioned sensors... I absolutely have to address him again on the PCM to look closer.

fst100

iTrader: (5)

a member just posted this thread from another thread. may be worth to read through to see if it may help you. The first notation looks interesting if you haven't checked it yet:
https://ls1tech.com/forums/automatic...e-problem.html

Saudrack

So, I now tried another PCM with same stock settings. Makes no difference in driving, hits also 6000 rpm and I also tried unconnecting MAF and TPS. Also with the other PCM no engine light going on, at reading for codes my cheap OBD reader said Faults: 0 and "attatched" errors: 2 (codes for low voltage MAF and TPS) I could not delete them, but at reading for codes again they were no longer there. That's weird, but it is so...

Talked to the mechanic again and he says the reason for the increase of the full throttle shiftpoint must be the torque converter, he talked from converter in and out speed... I didn't understand all he said, but the thing might be too much slip in the converter could cause a higher shiftpoint and the loss in acceleration ability that I feel. Now I really believe my converter is gone, anyway there is a longer time the problem I told, that the car also feels like it lost some torque. It feels a little loose in low rpm, if I step on the gas just so much to cause no downshift, the rpm goes up to maximum about 2500 and it also feels not as strong as it should and last but not least the power punch in the high rpms, it lasted the longest, but now it's also no more there...
The moments. the car sometimes has his power and shifts smooth, are completely gone lately. Now the car always drives shitty.
And lately I noticed the vibration when the car was parking. I revved the engine a bit and at about 2500 rpm came the vibration. All mounts from the engine and transmission seem to be tight, could not find something loose or weak.

The mechanic said I could buy a converter and bring the car to him. If there are more problems he will see.

I want to buy a stock converter, i don't wanna race, just sometimes push it to let the beast out and smile, but most of the time I'm cruising at low rpms.

I 'm confused there are two types, which some shops say both would fit, but I don't think so.

GM33CW has 10,75' bolt circle and 298 mm diameter and GM92 has 11' bolt circle and 300 mm diameter. So... Which one do I need? Does someone know?

Saudrack

Hello,

to keep you up to date: Last week I got the Camaro back from the shop. It stayed since November there.

The problem must have been in the valve body said the mechanic and another transmission specialist I asked. Some things with the pressure must have gone wrong, which caused the bad shifting, the temporarily 3rd gear vibrations (clutch shudder), slightly slipping, which made the car feeling not as strong as it should, and all those temporarily things. But the mechanic said there were no mechanical damages visuable by eye in the valvebody. Only dirt, just cleaning it helped not.
So there can things to wrong and it will never set a code to let you know where to look at.

Also the output shaft had rather big play and it began to leak there.

Now the car has a completely rebuilt transmission. At driving it home I liked it, noticed no delayed or hard shifts, no super sensitive downshift behaviour, all smooth and seems to be fine. I could not test the power properly, because there was too much traffic and slow vehicles on the road, but it felt strong, I think its ok. The mechanic has confirmed the power is good, it's how he knows it from other LS1 cars.

At home I immediately cleaned the car and washed away the salt from underneath. Now I hope the winter goes away fast and the salt away from the street, so that I can take the car out on the road again

One thing stayd same, it's the TCC always locking in 4th gear at 52 mph and only unlocks again with a downshift into 3rd. I immediately asked back to the mechanic and he said it's normal. The PCM commands it to do it this way. Only way to avoid this is a tune or driving in D at unfavourable speeds to avoid this unlocking with downshift-upshift-locking-unlocking with downshift-circle. TC is locked in 4th - you want to accelerate a bit - it's only very slightly possible with locked TC or just a downshift.
It seems, that it works so, because the car has the 2,73 rear axle and reaches top speed in 3rd gear. So the PCM is programmed to think that 4th is no acceleration gear. That's the theory.
I wonder if it woud work different, if the car would have the optional 3,23 rear axle?

fst100

iTrader: (5)

glad it was fixed finally! the TC is doing what its supposed to do, work as a overdrive. a lot of guys, like myself prefer to have the converter (TC) lock up only in 4th above 45mph on stock gear ratio (2.73 or 3.29) because any lower and it'll put more load and stuttering on the motor.
the TC should be unlocking if you depress the gas pedal down at a certain throttle percentage. I want to say anything more than 50% then the tc will unlock. if you have a local tuner they can adjust how sensitive the gas pedal is to unlock the TC as well as either tighten or loosen the firmess of the TC. you can make it lock without notice or firm and feel like a shift but too much from either spectrum can be bad on the TC.

Saudrack

Thank you.

I understand this.Yes it does unlock at a certain throttle posistion, but it stays not in 4th gear at this point. When it unlocks, it shifts down

fst100

iTrader: (5)

are you sure its the TC unlocking and not actually shifting down to 3rd gear? the 4-3 downshift occurs when the pcm senses the TPS at a specific percentage, for example, at 80mph it'll downshift from 4th to 3rd if you apply 75% throttle or more. at 80mph the TC would of unlocked before the 75% throttle because it was set lower for example, at 60mph.

Saudrack

I'm sure, it's unlocking AND downshifting into 3rd at the same time.

I try to explain it again:
If I accelerate in 3rd stronger, and the car shifts above that 52 mph into 4th gear, I can accelerate on in 4th with unlocked converter up to any speed. But when I take the throttle back it will lock. Then it will never unlock in 4th gear, with any throttle posistion, it does it ONLY in combine with a downshift into 3rd.

And when it's in 4th gear already under that 52 mph, it ALWAYS locks at that point. The rpms falls to about 1100 and the acceleration is bad then. If I want to accelerate a bit more then it's the same. It does not unlock and stay in 4th at the same time at any throttle posistion. It ONLY unlocks in combine with a downshift into 3rd.

fst100

iTrader: (5)

hmm odd, when the mph drops below a certain mph, the trans should be downshifting lightly as well to a lower gear and the tc would also. another way to test if the TC is unlocking while in 4th is when you're at a steady pace either foot lightly on the gas or not at a freeway speed, use your left foot and gently tap the brake pedal. the RPMs should rev higher because the tc is unlocked. I would have a tuner that knows about the LS1 take a look and adjust the tc lock and unlock settings to what other similar factory fbody 4l60e trans are set up.

Saudrack

I already tried this before the rebuilt tranny. Yes this works, when I press the brake pedal slightly it unlocks.


That's what I set out to do. I drive the car more in D at unfavourable speeds and if it still annoys me then, I 'll go back to the shop to let do another settings for locking and unlocking behaviour.
I don't know, it's factory update tuned by VIN. It's a EU-model, maybe it's a special EU-tune or so?

Tigavo

Grüezi aus der Schweiz

Just found this thread, i also have a '98 Z28 A4. My 4l60e feels the same with the TCC, especially when cold. Almost feels like 6-speed when the tcc closes in 3. and 4.

RPM WS6

iTrader: (3)

The TCC locking behavior sounds a bit odd, you should be able to get it unlocked without a downshift to 3rd (meaning, as mentioned above, adequate throttle input in 4th gear should unlock the TCC while still keeping you in 4th). Gear ratio (2.73 vs. 3.23) wouldn't prevent this from being the case. If it unlocks when you tap the brakes (as it should) then it might have more to do with tuning rather than a failure of some kind. I don't know if lockup tuning is different for EU-spec models.

RevGTO

iTrader: (12)

Locking and unlocking are controlled by a combination of VSS & TPS input - vehicle speed and throttle position. IIRC, the stock tune commands lock-up at certain speed regardless of throttle position. Unlocking is commanded by a combination of both, but at a certain speed it unlocks automatically regardless of throttle position.

For instance, in my tune the converter locks at 45mph and unlocks at 42. It doesn't downshift when unlocks, the clutch just lets go. You should experience the same when you're cruising and vehicle speed drops below the designated threshold - without a downshift.

Saudrack

Right. When I slow down to 43 mph or below it unlocks without throttle or downshift. And if I stay in 4th then and go up to 52 mph it will lock again, even when I 'm accelerating. It does this every time and it sucks.
I'd like to be able to unlock the converter in 4th without a downshift, but this is definitely not possible in my car. It stays locked until the throttle posistion where it shifts down into 3rd.

If your cars are different, then it seems to me that the EU-tune is really different in TCC settings.