High RPM misfire mystery...

[martymil]

You could try a new flywheel but I don't think it will help
and it's going to be an expensive maybe

the only way is, either go a smfw or turn the boost down

i would turn the boost down a little or taper it down up top just before it starts to misfire
as this is the cheapest option and all you sacrifice is a little bit of power up top

[Artsoasis]

Doesn't happen if I shift under 6600 rpms. So I'll just do that.

[AWSAWS]

Doesn't happen if I shift under 6600 rpms. So I'll just do that.

Running anything like meth injection?

[Artsoasis]

Running anything like meth injection?

Nope.just 100% e85 with PI

[AWSAWS]

Nope.just 100% e85 with PI

I asked as I've been looking at some of my logs and seeing an imbalance between the flow of meth to banks 1 and 2. If you were running meth I was going to suggest looking at the fuel trims. Not enough octane (to one of the banks) might cause issues such as misfires with high boost like you are running but it sound like your setup shouldn't suffer with that.

[boostedbmw89]

Hey fellas..bringing this back from the dead again. Im having the same problem. Changed to index 12 injectors, precision raceworks coils, new plugs gapped at .020 and its always cylinder 6. I have a 2008 335xi full bolt ons and like everyone else said its high boost/high rpm/high load situations. I did logging and everything looks perfect. Full e85 port injection and stage 3 fuel-it pump. I cannot get away from this damn cylinder 6 misfire. Its a 6AT and im not to sure about turning of misfire detection. I have a dyno day monday at 9am would love to figure this out before going in

[Itsbrokeagain]

How's the injector seat in #6 ? I saw a few times on an e60 where the rubber seal at the end went bad and hot combustion gases opened the hole up slightly, causing a permanent misfire. No new seal would fix it as it was now too loose to seat properly, burning it out within hours of installing.

The only cure was installing another head.

[nyt]

I went through all of this with my 6at xi. I ended up disabling misfire detection about 6krpm. Not ideal, but couldn't get rid of it any other way. Always cyl 6

[Sticky]

I went through all of this with my 6at xi. I ended up disabling misfire detection about 6krpm. Not ideal, but couldn't get rid of it any other way. Always cyl 6

Anyone know why it is always 6?

[martymil]

DMFW

[AWSAWS]

Anyone know why it is always 6?

Well I'll tell you something quite interesting. I was getting cylinder 6 misfires top end as well. Like over 6000 rpm. Sometimes 5 and 6. What I noticed on my DIY meth injection, (that has the nozzle holders on the top of the manifold) was that holders 5 and 6 felt really cold, compared to 1-4. 1 to 4 actually felt hot from the heat transfer off the manifold. My theory is that on my setup, under hard acceleration (G force), the meth was being drawn more to the 5 and 6 lines due to the G force. So getting more flow. Possibly a bit too much. Staying on it with a 5 and 6 misfire must have thrown 4 off as well and probably the other cylinders, getting the multiple cylinder misfire scenario. The lambda codes were from my check valves not being strong enough to cut meth flow quick enough when letting off the throttle.







So what I did was to route lines from the right side of the 6 way meth block to cylinders 1 and 2 instead of 5 and 6. Then I routed the 1 and 2 ports to 5 and 6. I haven't had the issue since. So my rear cylinders get meth from the front of the block and vice versa.

So I don't know with you guys with port injection. Injector 6 may have the most pressure in the fuel rail and be doing the same thing. Maybe someone with the cylinder 6 issue could try limiting fuel from that injector some way to see if it helps. Smaller injector?

Anyway this solution seems to have solved my problem.

[AWSAWS]

Running lines like that is a bit untidy. Looks like this

[martymil]

He hasn't got meth and he is dct so meth wont apply

You need.to look at your inlet temps, injector seal on 6

Have you done a comp test and a leak down test on 6

We had the same issue on dct here in oz so we changed to a dmfw from an m4 and no more missfires

[AWSAWS]

He hasn't got meth and he is dct so meth wont apply

You need.to look at your inlet temps, injector seal on 6

Have you done a comp test and a leak down test on 6

We had the same issue on dct here in oz so we changed to a dmfw from an m4 and no more missfires

He has port injection. Which makes me wonder if it's a similar fuel distribution issue. Is it possible to adjust the fuel per injector or do they all just fire together off the same signal?

[martymil]

Currently they all fire of the same signal or batch fire.

DCT in the n55 135 runs into the same issue as 135, 335 and 1m prior to the m4

You get false knock from the DMFW but you must run the checks I mentioned earlier,

If it passes all those test its most likely the flywheel and you need a dct flywheel from a m2 to overcome it.

[Sticky]

Sometimes 5 and 6. What I noticed on my DIY meth injection, (that has the nozzle holders on the top of the manifold) was that holders 5 and 6 felt really cold, compared to 1-4. 1 to 4 actually felt hot from the heat transfer off the manifold. My theory is that on my setup, under hard acceleration (G force), the meth was being drawn more to the 5 and 6 lines due to the G force. So getting more flow. Possibly a bit too much.

It's an interesting theory.

Does this tend to happen only with meth setups like yours?

No misfires since you changed the lines?

[AWSAWS]

Since running the lines back to front and front to back I haven't encountered another misfire. My situation may have been different but I can imagine with a stock inlet that the air/fuel ratio on bank 1 and 2 could be quite different. Just due to the path of air into the manifold itself. I'd wonder if injector 6 sprays a little more fuel than injector 1 due to gravity under acceleration but surely fuel trims should adjust for these things.

Next time I do a pull and the engine bay is really hot I'll quickly get out and feel the temp of the nozzle holders again.