Z4 Stg2+ Relentless Cyl 6 Missfire

[finnc0]

Hey! I'm new here, thought I would ask this as I'm at my wits end trying to figure this one out.

As the title says, I have a Cyl 6 miss that keeps popping up when doing a WOT pull from 2500-6500 in 3rd gear.

All injectors have been replaced with USED index 12's
All coils have less than 6k miles (eldor)
All plugs are NGK 97506 gapped at 0.022"
VRSF Chargepipe & Downpipes.

HPFP was replaced 2-3 months ago

Things I have attempted:
* swapped plug and coil, miss still stayed on cyl 6,
* swapped injector to cyl 5, the miss actually went to cyl 5 to which I then replaced the injector with a brand new index 12 in cyl 5 which FIXED the cyl 5 missfire however cyl 6 started missfiring right after when doing the same WOT pull in 3rd.

I have another index 12 new from FCP on the way to try and swap with the cyl 6 one.. again
I have a feeling it may be the flywheel..


Any thoughts or ideas would be really appreciative. Thanks!

---------- LOGS ---------

Logs WOT 3rd gear: https://datazap.me/u/finncarmichael/fbo?log=0&data=3-13

I made around 407hp last month until this problem started happening. Now making between 320-360.

Last known good WOT 3rd gear log (no issues): https://datazap.me/u/finncarmichael/fbo?log=0&data=3-13

[B21]

The 'classic' cyl 6 misfire is alledged to come from the knocl sensors detecting a false superknock event..

This is caused by something 'rattling' in a way that sounds to the knock sensor like a pre ignition event.

DMFW are asserted to be one cause..

I've had this as I explored the 550 bhp part of my hybrid turbo tune..I've backed it off to remove this issue..

It could have been actually my Nexsys ignistion rail bracket loose..I'venot gone back to check it..

I do have a brand new M2 FMFW ready to fit as and when I'd got to drop the fearbox!

[finnc0]

B21, is there any way to test if it's the DMFW or do you kinda just have to replace it with the M4 one for the misfire to go away.
Also, I am only making prolly around 420BHP, you state you we're getting the issue around 550BHP, is it strange that I'm getting this issue (possibly the DMFW) at a much lower HP?
Shop is doing another diag this week, going to scope the CPS and see if they see anything abnormal. All valves appear to be opening and closing correctly, none stuck open. If all that checks out, will most likely proceed with getting a M4 flywheel installed. Will keep updated.

[B21]

Originally Posted by finnc0

B21, is there any way to test if it's the DMFW or do you kinda just have to replace it with the M4 one for the misfire to go away.
Also, I am only making prolly around 420BHP, you state you we're getting the issue around 550BHP, is it strange that I'm getting this issue (possibly the DMFW) at a much lower HP?
Shop is doing another diag this week, going to scope the CPS and see if they see anything abnormal. All valves appear to be opening and closing correctly, none stuck open. If all that checks out, will most likely proceed with getting a M4 flywheel installed. Will keep updated.

There are many theories about exactly what it is that causes this cyl 6 misfire..I spent a lot of time and was offered 3 options ..reduce peak horsepower, reduce knock sensitivity or fit m4 DMFW …

So I’ve backed of peak BHP whilst waiting to fit my new DMFW

Strange your misfire did move but I’m afraid apart from A:B substitution or just checking EVERY piece of metal to metal for looseness / rattling

[finnc0]

Understood. Did drop the trans earlier this year to fix the dreaded mechatronics electrical connector oring seeping, maybe something is rattling or loose under there. Will look into that. Have to get walnut blast done so will do that anyways, otherwise looks like I'll be putting in a M4 flywheel within the week / next week. Might get shop to check/scope O2 sensors and check the ground strap.. it'd be funny if it was one of those, lambda and fuel trims look decent so I doubt its the o2's... maybe ground strap, well see.

(I did attempt to desensitize the knock tables with MHD however the misfire still occurred, it felt like it was a bit harder to get it to misfire but maybe that was a placebo)
I should mention on STG0 no misfire occurs at all, it actually shifts a lot better too.

Thanks for the recs and assistance so far. Will keep this thread updated.

[B21]

Originally Posted by finnc0

Understood. Did drop the trans earlier this year to fix the dreaded mechatronics electrical connector oring seeping, maybe something is rattling or loose under there. Will look into that. Have to get walnut blast done so will do that anyways, otherwise looks like I'll be putting in a M4 flywheel within the week / next week. Might get shop to check/scope O2 sensors and check the ground strap.. it'd be funny if it was one of those, lambda and fuel trims look decent so I doubt its the o2's... maybe ground strap, well see.

(I did attempt to desensitize the knock tables with MHD however the misfire still occurred, it felt like it was a bit harder to get it to misfire but maybe that was a placebo)
I should mention on STG0 no misfire occurs at all, it actually shifts a lot better too.

Thanks for the recs and assistance so far. Will keep this thread updated.

Please do!

[finnc0]

UPDATE: Bought a LUK M4 flywheel and my shop is installing it today along with doing rear main seal as it wasn't much more and might as well do it while it's out.

When they dropped the trans, they could immediately tell the DMF was bad, it had a bunch of play and was definitely toast. The flex disc/guibo was also bad, they should be done later today with both of those things and will update if it fixes the misfire. Most likely will as the DMF was on the brink of shearing off due to how much play it had.

[B21]

Originally Posted by finnc0

UPDATE: Bought a LUK M4 flywheel and my shop is installing it today along with doing rear main seal as it wasn't much more and might as well do it while it's out.

When they dropped the trans, they could immediately tell the DMF was bad, it had a bunch of play and was definitely toast. The flex disc/guibo was also bad, they should be done later today with both of those things and will update if it fixes the misfire. Most likely will as the DMF was on the brink of shearing off due to how much play it had.

Great update thnx..how many miles has the DMFW done?

[finnc0]

So new flywheel (M4 F8x Luk) fixed all the misfires and hard shifting I was getting on stg 2+. Ill send a video later today showing the play in the flywheel.. it was crazy.
DMFW had 148k miles and we could tell it was the factory one for sure. Plan to upgrade turbos on this thing so glad I got this sorted out.

[finnc0]

Heres the vid showing the play in the DMFW

https://streamable.com/np19eh

[B21]

Originally Posted by finnc0

So new flywheel (M4 F8x Luk) fixed all the misfires and hard shifting I was getting on stg 2+. Ill send a video later today showing the play in the flywheel.. it was crazy.
DMFW had 148k miles and we could tell it was the factory one for sure. Plan to upgrade turbos on this thing so glad I got this sorted out.

Fantastic news …great research and analysis…