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Old 12-16-2018, 07:12 PM   #21
Overboost
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Quote:
Originally Posted by rkneeshaw View Post
This little guy was the culprit. New box on the left, old sensor on the right



Installed the new crankshaft position sensor and car runs great all the way to redline.
Nice to get it figured out. Ahhh...
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Old 04-14-2019, 03:53 PM   #22
rkneeshaw
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ok so I was wrong, that crankshaft sensor did not fix the issue.

After the car sat all winter in storage, I decided to also replace the headers. My ebay headers were 10 years old and had 100k miles on them, and I suspect I had a slight exhaust leak. Desperate, I replaced them with bimmerbrakes gen 3 headers, but that did not fix my misfire issue either.

So now the list of things I've tried looks like this:
  • Swapped spark plugs and coil from cyl 6 to 1
  • Also replaced spark plugs with new plugs
  • Replaced cyl 6 fuel injector and inspected the electrical connector
  • Confirmed AFR of about 11:1 at the time of the misfire (suggesting the fuel system is keeping up fine since its not leaning out)
  • Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours. Resealed manifold to head, fresh gaskets, torqued to spec.
  • Compression tested: between 209 and 211 psi across all 6 cylinders
  • Free-rev to 6k RPM, held there, no misfires, it only happens under sustained load
  • Installed M3 motor mounts to match M3 trans mounts
  • Flashed known good tune to the car, still misfires
  • Replaced headers and installed all new hardware and gaskets, confirmed no exhaust leaks

This misfire problem only started after having the clutch and flywheel replaced. I've driven the car hard all summer and it wasn't an issue until that night on my way home from the shop after the clutch and flywheel install.

I feel like I've cleared every "real" source of a misfire (fuel is good, ignition is good, air is good), so I'm still thinking the problem has something to do with the detection of the misfire itself.

I mean, is it possible the new clutch and flywheel combo changed harmonics or something in just the right way that the DME thinks it detects a misfire?

I'm running a LUK OEM-style dual mass flywheel with a Sachs Performance clutch, and in case it matters I have an ATI super damper on the other end of the crank.
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Last edited by rkneeshaw; 04-14-2019 at 03:58 PM.
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Old 04-15-2019, 09:57 AM   #23
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Maybe it's time to replace both engine wiring harness and ms45 ecu itself?
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Old 04-23-2019, 09:39 AM   #24
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MadToha, maybe, I'm open to any ideas at this point.

I just tried replacing all coils with new, no change.

As a workaround for now, I used ByteTuner to change c_mis_max_nr_off_iv to 0 in the DME tune. This value controls how many cylinders are shut down when a misfire is detected. Default value is 2. I changed it to 0. I don't have cats, so no need to shut down cylinders if there's a misfire. Now when it does occur I get a single brief flash of the SES light, but otherwise I can't tell anything is going wrong, the car actually drives so good, I'm having so much fun driving it.

Updated list of things I've tried:
  • Replaced all 6 spark plugs with new
  • Replaced all 6 coils with new
  • Replaced cyl 6 fuel injector and inspected the electrical connector
  • Confirmed AFR of about 11:1 at the time of the misfire (suggesting the fuel system is keeping up fine since its not leaning out)
  • Removed the ESS manifold and pressure tested to ensure the intercooler wasn't leaking coolant into the cylinder, pressure tested good, held 11psi for over 4 hours. Resealed manifold to head, fresh gaskets, torqued to spec.
  • Compression tested: between 209 and 211 psi across all 6 cylinders (gauge is out of calibration, its probably 20-30 psi off)
  • Free-rev to 6k RPM, held there, no misfires. Also drove in 2nd gear and held RPMs at 6300 for a few seconds, no misfires. It only happens under sustained load such as in 3rd+ gear wide open throttle.
  • Installed M3 motor mounts to match M3 trans mounts
  • Flashed known good tune used on prior track days to the car, still misfires
  • Replaced headers and installed all new hardware and gaskets, confirmed no exhaust leaks

I'm starting to doubt some of my tests at this point, such as the pressure test I did on the ESS manifold. I applied 11psi to the inside of the intercooler circuit, which is the opposite direction of the pressure applied when the car is under full throttle. I should have applied vacuum to that circuit to better replicate the real world.

I guess the only other thing I could validate is the wiring harnesses like MadToha mentioned. Ignition looks solid, and it routes in a place that wouldn't be effected by the clutch job, and its right on top, and everything looks super clean with no cracks in the sheathing etc. But the fueling wiring harness is harder to inspect due to it routing behind and below the huge ESS manifold.

I'm going to run a fresh log on the car to validate fueling stays strong, which I believe it does, but can prove it now that the DME isn't shutting down cylinders when a misfire is detected.

It seems like these are the remaining possibilities at this point, probably in order of likelihood:
  • Intercooler coolant leak
  • Fueling wiring harness fault
  • Cam sensor failing intermittently? (seems highly unlikely or the symptoms would be different?)
  • Harmonics issue with the ATI damper, Sachs performance clutch, and OEM-style LUK dual mass flywheel (also seems highly unlikely)

I cant think of anything else that it could possibly be, anyone else have any thoughts on this?
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Old 04-23-2019, 10:35 AM   #25
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It could be just bad connection from coil side or ecu side of the wiring. Temp solution is just to minimize gap in contacts with some hard needle.. I fixed MAF and ICV connections this way many times, then installed new connectors repair set.
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