[OpenFlash]

UPDATE (12/26/12): Confirmed solution. Georgiatech335i replaced his stock dual-mass flywheel with a single-mass flywheel and the misfire is gone

Hi guys,
In the last few weeks, 3 newly-installed single turbo n54s ran into a high RPM (~6500rpm) misfire problem. One local (tmo335tt) and two in florida. This came as a surprise to us given how many 6MT VFF single turbo cars are running around problem-free. We tried everything from updating DME software, revision CPS algorithms, changing torque limits/calculations in the flash, etc,. Short of disabling misfire detection in our flash (yuck), nothing seemed to solve the problem. We were working with tmo335tt for some time with this and it's a good thing that this problem happened to him because I don't think anyone else would have spent enough time figuring out the cause of the problem. Which he did.

The problem has to do with the factory dual-mass flywheel that twists at high torque levels. Combine that with high RPM (where misfire diagnostics is most sensitive) and you get a misfire fault without the real misfire. It also explains why the the only three misfiring Single Turbo 6MTs have stock dual-mass flywheels while all others have single mass lightweight flywheels. I also recall BMW themselves changing the clutch/flywheel assembly on the 1M for this reason. And that is only with a small power bump.

So no, the proper solution isn't to mess with the knock tables or to disable misfire detection (which I did today on tmo335tt's car until his new flywheel comes in next week). The real solution to run a suitable flywheel that is capable of withstanding the higher torque loads that upgraded turbos (and sometimes even stock turbos) are capable of supporting. Other option is to just make less power I suppose.

Hope that helps those 6MTs (like BigTom, IIRC) that were battling high rpm misfire. And big props for tmo335tt for wrapping his head around this and figuring this out. It will undoubtedly save a lot of people headache in the future as they try to make more and more power.

Cheers,
shiv

P.S. Here is some good info on the subject of dual-mass flywheels and misfire detection:

http://papers.sae.org/2007-01-3544/

Shiv

[Sered]

Thanks for posting this Shiv. Much appreciated!

[Fully_Bolted]

Awesome. One question, how does he know its the flywheel if he's waiting on a replacement? Did he have a flywheel to test?

[Tim M]

I'm impressed! That's an engineering accomplishment!

[AK 335i]

Originally Posted by Fully_Bolted

Awesome. One question, how does he know its the flywheel if he's waiting on a replacement? Did he have a flywheel to test?

[cn555ic]

Interesting. Glad u guys found the solution To the problem

[OpenFlash]

Originally Posted by Fully_Bolted

Awesome. One question, how does he know its the flywheel if he's waiting on a replacement? Did he have a flywheel to test?

At this point, I think we have enough data to reliability come to this conclusion. We have 7 single turbo 6MTs with single mass flywheels with no such problem. And 3 single turbo 6MTs with stock dual-mass flywheels with this problem.

Unless I'm mistaken I think even Dzenno, who eventually resorted and routinely recommends disabling misfire detection, also has a stock dual mass flywheel (but now with a fully built head). The latter didn't fix his misfire issue. Because the issue wasn't engine-related.

Shiv

[Eric335]

Originally Posted by shiv@vishnu

At this point, I think we have enough data to reliability come to this conclusion. We have 7 single turbo 6MTs with single mass flywheels with no such problem. And 3 single turbo 6MTs with stock dual-mass flywheels with this problem.

Unless I'm mistaken I think even Dzenno, who eventually resorted and routinely recommends disabling misfire detection, also has a stock dual mass flywheel (but now with a fully built head). The latter didn't fix his misfire issue. Because the issue wasn't engine-related.

Shiv

Very interesting results Shiv. Glad to hear you figured it out. The whole community appreciates it

I kept thinking of Dzennos car as i was reading your thread, and then i saw what you mentioned. Interesting results that you came up with.

Thanks,
E

[Wedge1967]

So my chances of buying Trevor's turbo kit for pennies on the dollar is no longer a possibility?


Good job guys.

[cn555ic]

Originally Posted by Wedge1967

So my chances of buying Trevor's turbo kit for pennies on the dollar is no longer a possibility?


Good job guys.

Should have jumped on it real quick. It was a matter of time getting the solution. Shiv having surgery didn't help either to expedite the solution. But either way glad there seems to be a fix. Looking to hear results

[Wedge1967]

Originally Posted by cn555ic

Should have jumped on it real quick. It was a matter of time getting the solution. Shiv having surgery didn't help either to expedite the solution. But either way glad there seems to be a fix. Looking to hear results

Yeah... I think if I would have had 20k on me before shift sector while we were working on it at FFTEC, he would have took it. That was a very frustrating weekend for him and a few other people who didn't make it... Can't wait to see what the solution will be for the AT cars.

[Fully_Bolted]

Originally Posted by shiv@vishnu

At this point, I think we have enough data to reliability come to this conclusion. We have 7 single turbo 6MTs with single mass flywheels with no such problem. And 3 single turbo 6MTs with stock dual-mass flywheels with this problem.

Unless I'm mistaken I think even Dzenno, who eventually resorted and routinely recommends disabling misfire detection, also has a stock dual mass flywheel (but now with a fully built head). The latter didn't fix his misfire issue. Because the issue wasn't engine-related.

Shiv

Very cool, as a 6MT owner, want to give a big THANK YOU to Tmo335i

[JamesM3M5]

I wonder whether age and wear on the flywheel and/or vibration damper can contribute to this phenomenon. All in all, that's one incredible find!!

[AK 335i]

6 people that were diagnosed with aids this week didnt smoke ciggarettes.

The 17 that didnt get aids do smoke.

We have deduced that smoking ciggarettes is the cure to aids.

Your welcome

[redlineryder]

To be fair, this is still theory and still unproven. Until such a time as the current 6MT ST misfiring cars install SMFW's and the misfiring goes away you are just assuming this is the problem.

[themyst]

interesting find.

[AK 335i]

Originally Posted by themyst

interesting find.

YeAH the best part is Malboro stocks are still low. If you buy now, its an easy retirement

[themyst]

Originally Posted by smi1gj

YeAH the best part is Malboro stocks are still low. If you buy now, its an easy retirement

cool i guess.

[MDORPHN]

Really interesting stuff.

Am I correct then that the problems encountered by single turbo folks with auto trannys are completely unrelated?

Thanks and props to you and tmo335tt.

Neil

[Ænema]

What direct evidence is there that it's the DMFW? I just have a hard time seeing it being the FW.


Are you saying it's because of the harmonics or the slight give between the separate sections of the FW?

Have you had the car hooked up to an oscilloscope to verify the signal interference?

[OpenFlash]

Hi guys,
I just posted up what I believe to be the cause based upon supporting evidence I've gathered. And this does include scope readings of the CPS waveform at various loads/rpm. What happens to the square wave at high RPM/high load, with a DMFW, is pretty interesting. I'll post up more data once tmo335tt installs a new FW in his car. But the link to the SAE papers that I posted in the first post should explain things for now. I'm not trying to sell people clutches. Nor do I have any stock in Spec, Tilton, etc,. I'm just posting our findings based upon the data collected. By no means do I suggest going out and replacing your stock DMFW. Unless you have a 6MT and are making over 500whp, it's unlikely to cause an issue. But if you are making big power and have had to disable misfire detection to prevent a high RPM limp mode, this is just something that you can look at.

shiv

[DallasBoosted]

Just as a random question, whats the downside to disabling misfire detection?