E46Fanatics - View Single Post - Stumped: Misfire cyl 6 above 6k RPM
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Old 04-14-2019, 02:53 PM   #22
rkneeshaw
Registered User
 
Join Date: Oct 2008
Location: Northern Michigan
Posts: 1,649
My Ride: 330i ZHP
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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2003 BMW 330i ZHP
ESS Twin Screw Stage 2+ - Wavetrac - Headers - Borla - BMW Performance
Turner Motorsports - Powerflex - Hawk Performance

Build thread: https://forum.e46fanatics.com/showthread.php?t=696662
Wheelwell: 2003 BMW 3 Series
Fuelly: 2003 BMW 330i ZHP

Last edited by rkneeshaw; 04-14-2019 at 02:58 PM.
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