Silk

I made today my first meters at a track. Got some 3hrs of driving time in total, in blocks of 25-30mins.

Not too crowded on the track, so perfect to build up confidence. I got a full 2hrs of an instructor next to me so I made good progress ... and of course had a lot of fun.

Amazing how fast the other cars were ... Cayman gt4 club sport, 991 turbo s, 991 gt3 rs

But ... The following things caught my attention and maybe some of you can point me towards a possible cause.

The car is a 2002 c2 tiptronic, spin on oil filter, ipd plenum, sports headers, adapted cooling (waterpump, low temp thermostat and relocated), x51 oil pan, motul 300v, ohlins road&track suspension, Yokohama AD08r

1. Towards the end of each block I noticed some significant loss of power. The car did not pull hard anymore. Very Noticeable at the straight. Very slow acceleration. Lets say above 4500rpm in 3rd and 4th gear the power was completely gone.

2. During upshifting the tiptronic hesitated as if the torque converter was engaged a split second later. Noticeable in a small rpm 'hickup' or glitch. Downshifting was smooth an reactive.

Water temperature stable. Needle on 0 of 180 where on the street it stays around the 8. Outside temp 28C

On the street under normal driving conditions the car performs strong. Pulls hard. The tiptronic reacts fast, shifts very smooth. Has been cleaned and flushed 20.000miles ago

What could cause this behaviour. Is it somehow a ECU related issue. What are the steps I should /could take to investigate further.

Will go to the mechanic to get a read out for possible fault codes.

5CHN3LL

What you're describing is VERY strange - I've never had the car retard power for me, even when hot and doing long, hard pulls - like a solid 30-40 minutes going from sea level to 8,600 feet @ 85 degree ambient air temps. Even at 8,500 feet, my 996 pulls all the way to redline after being flogged for 50-60 miles. Of course, my apple is a manual compared to your Tiptronic orange.

It sounds like the ECU was retarding timing or otherwise reducing power - but I have no idea why this would happen. I don't know anything about tips, but there are a number of conditions with the tip that will put the car in Reduced Driving Program (limp) mode.

Silk

It is not limping ... I still reach 160km/hr at the end of the straight. But in the beginning of each block I was easily reaching 185-195. After some rounds performance would drop.

It seems like missing torque. I also think that issue 2 is just a result of 1 ... Maybe some timing issue in the engine which offsets the tiptronic shifting sequence.

Driving home I did some pulls on the highway and it shifts flawless

5CHN3LL

OK, I'm now confused. The car not being able to accelerate beyond some RPM ("above 4500rpm in 3rd and 4th gear the power was completely gone") seems rather more severe than "it's missing torque."

The fact that you can feel the transmission acting funny when you encounter this behavior still makes me suspect that the Tip is messing with output. In addition to the Draconian limp mode which limits output to something stupid like 10mph, I'm guessing there are other codes/conditions for the Tip that can cause the DME to reduce output/retard timing, but the Tip is a mysterious and unknown entity to me.

Silk

It accelerated beyond 4500-500rpm but ver slow. Hence it does not pull. So it feels as if there is no torque available. Does that comparison makes sense?

Could a dying torque converter behave like this? Temperature dependent? I know that they can be difficult to correctly diagnose if they are at the verge of failure.

Now that I think more about it. Something does offset the tip behaviour because I had the impression when in D mode it did not stay in the most sporty mapping. I found it sometimes shifting to even 5th over the more curvy parts whereas 5th would be only make snse on the straight (not even).

How does the tip-ecu-throtlle communication works? Did the engine not revved fast enough so it did not engaged the most sporty drive mapping?

I did not think about to do a recalibration of the e-gas at that moment.

MoeMonney

It could be a failing coil pack. You should check them. If they fail they make the car hesitate and loose power on acceleration. Did you get a check engine light?

garrett376

The intake switchover valve not working will significantly reduce power after 4800-5000 RPM range. I had that happen on my 02 race car and I'd shift at 5000RPM because there was no reason to run the engine any higher from a power standpoint, it's that noticeable. Check and make sure this is functioning properly as it can completely fail and not throw any codes yet the engine just feels gutless above 4800 RPM or so. And it's a fairly cheap part and easy to access to replace if it is your cause.

ion_berkley

I know very little specifically about Tiptronics, but have generic observations about torque converters...any chance that the transmission fluid was just starting to get hot and the torque converter was slipping more? Certainly my (very non 996 like!) truck behaves as you have described in hot ambient temps after hard driving.

Silk

Could this switchover valve be influenced by the engine temperature? Under street driving everything goes strong till redline.

Will check coil packs. Could this be temperature related? Again under street conditions it pulls strong till redline.

Another thing is I washed the car with a hose the same morning, could it be that something got wet.

To be complete, I had the sports headers, larger throttle body and IPD plenum installed two weeks ago. The accompanied air intake tube was modified by my mechanic because my car had this air breather hose from the tiptronic connected to it. He made a connection for the tube in the new intake pipe where the tube attaches to, so the configuration is in fact the same way as before. He found the esthetics of a loose filter attached to the breather hose in the engine compartment a no go!

Silk

No CEL whatsoever.

Silk

Could be ... Hard to diagnose though. Cooling water temperatures were still moderate though. I have no knowledge how hot the ATF gets under high performance driving.

Silk

Ok, i got the car scanned for codes.

- ATF temperature too high code was flagged (I do not remeber the code number, but i suppose it was P0218)

So this one directly points to a overheating scenario. ATF too hot, ECU overrides throttle response via e-gas. Which explains also that the transmission switched to a less sporty mapping at some point s on the track. Does it also explains the hesitating engaging of the tranmission during upshifts.

- 5525 torque transfer from DME disturbed at times, no fault symptom available.

This one seems PSM related, no idea if it has something to do with the tack driving yesterday. Some months ago I participated in a driver training aimed to learn the limits of the car and what to do in these situations. Could be it got triggered there as PSM kicked in various times.

Is it normal that the tiptronic overheats so fast? Or do i need to look for a problem in the cooling.
Should I also investigate further items such as torque converter, ... ?
Anyway I will go and let the transmission flushed, see what comes out and if the fluid looks clear.

spruden

I've never experienced any symptoms like you describe in my manual C2, however managing heat and load on various systems is common. Especially as you advance in the faster run groups. The early tiptronic isn't known for being particularly robust - so you may need to alter your driving to compensate for the heat.

It's not uncommon to shift a bit early, turn on the heater, take a lap at 60%, etc to give you and the car a bit of a break while on track. Remember you're learning how to drive your unique car fast - mentally, physically, and mechanically (including quirks).

Also, I've seen several scenarios where bolt-on, go faster bits cause strange issues when pushed hard - especially involving heat management. This seems to be very common with the late model performance GM cars.

Silk

Thanks for the input ... My level is not that high so I did not push the car very very hard. So I was surprised to see that it lost performance so quick. Even that it was not extremely hot.

Nothing indicates to overheating of the rest of the engine. Water temperatures stayed around 180-190F. Oil pressure around 1.2-1.3 when idling after a last slower lap.

The 996 mk2 has a different tiptronic then the early 996. The mk2 has the one that is in the 996 turbo. Which is considered as almost bullit proof.

I hope it is just an issue with the ATF level or eventually a bad torque converter.

Edit:
I spoke with my mechanic on the phone. He thinks the tiptronic switching unit could be the culprit. He says that it does not switch as fast and smooth as should be and that probably at higher and more prolonged load and temperatures it starts to lag further. Which causes additional extra heat generated etc etc. I myself would have no idea, it is the only tiptronic I drove till now, so difficult to compare. I thought it shifts not bad at all. He will test drive it again to see how it behaves under different circumstances.

I trust him on this matter. So I will at least have it checked and opened up for cleaning. The ATF will be drained anyway, so a check on how the ATF looks like will be done. From there on we see If there is any visible wear. If replacement is required, he said that the switching unit is a part form Mercedes and available at a reasonable price and he did already revise several tiptronic gearboxes this way. He does not believe that the torque converter has problem. He says the transmissions are very very strong. Only the switching units are a weak point as thea are partly made of plastic.

To be continued.