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      03-13-2020, 12:20 PM   #27
widetyres
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Drives: M3 E92 DCT, 2012
Join Date: Oct 2018
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Quote:
Originally Posted by Nezil View Post
I did some further testing today to see if the waste gate delay was caused by the DME seeing the clutch position, or due to simply getting back on the gas from a 1 second lift off. To do this I conducted 2 tests:
  1. A 'no lift shift' from second to third: https://www.bootmod3.net/log?id=5e6a...0b4350057969b9
  2. Going from floored in gear, to lifting off for 1 second (no clutch) to floored again: https://www.bootmod3.net/log?id=5e6a...0b4350057969bd
Both of these cases resulted in no waste gate drop when back on the gas!

The second test was quite informative because it does show the same boost drop when you lift, but has different characteristics when you floor it again. Wastegate is pegged at 100% from only 62% pedal position and stays there until the boost target is met... as I would expect.


The 'no lift shift' felt pretty terrible; a big shock to the drivetrain, and I don't think I'll be doing that again in a hurry. Boost was held through the shift, so the waste gate never had to close, so I'm not sure how useful this test was.

The next test I plan to do is shifting up without the clutch. This is slower than with the clutch, because you have to wait for the revs to drop to match the gearbox speed, but it is pretty easy to do on an upshift. This should indicate if it's the clutch signal to the DME that is causing the waste gate delay because it doesn't seem to be present when you simply let off the gas.
I love this thread Nezil as the lag also bothers me sometimes.

When I used to have a porsche boxster I shorted the clutch switch so that the dme always thought the clutch was always engaged - this made a massive improvement to the responsiveness of the engine immediately after shifts.

A while ago I did contemplate doing the same thing with the m2, but backed off as I thought the dump valve might not open and it'd cause alot of issues. I didn't then have Bm3, but now do so logging/checking would be easier.

Still it could be worth investigating. If the dump valve was opening ok with the clutch shorted (which actually it should be as the pressure is controlled regardless of clutch position), then things like hill start and cold engine rev assistance would stop - hey, it'd be exactly like driving a car from 15 years ago (which is a good thing imo!).
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