Technical Unsolvable cyl #5 misfire - Tried EVERYTHING

[Catalin335xi]

Hello,

First and foremost, I've been searching for a solution for this through all imaginable forums, youtube videos, going to shops etc for almost a year, still haven't found a solution. Also posted this another forum but got no replies there

The problem
My problem is a persistent misfire on cyl #5, the higher the boost the more likely it is to happen. It always happens above 6k rpm and only in wot. It always happens on#5

My car
Running 26.5psi
N54 built engine (JE pistons, FCP engineering rods)
Turbos TTE680
Index 12 injectors, new hpfp, walbro 525 lpfp, 3.5bar tmap, everything down to the boost solenoids and vacuum lines is new
Sparkplugs 2 step colder and S55 coils - I ran this boost on this setup with no issues until this problem started

What I already tried
No active codes (except when it happens the misfire code on #5)
No timing corrections prior to the misfire
STFTs, AFRs, looking very healthy
Swapped plugs
Got a new set of plugs
Swapped coils
Checked coil harness to and from the DME
Got new coils
Swapped injectors
Got a new injector with new seal and decoupling element
No injectors have any sign of blowby
Compression test is good on all 6 cyls
No carbon deposits anywhere in the engine is it was rebuilt 15k miles ago
As I've heard that a built engine can have a different sound and trick the knock sensors into registering knock, I've checked the "Desanitize the knock tables" from MHD and yet nothing changed.
Checked the PCV valve (which is upgraded aluminium) - it looks perfect
My mechanic as well as my tuner have ran out of ideas.


I am at a loss of what could be causing this. I cannot think of anything else to test. I would really appreciate some input from you guys as I've been blasting my brains for a year trying to find a solution for this. Thanks.

 

[SlowE93]

Hello,

First and foremost, I've been searching for a solution for this through all imaginable forums, youtube videos, going to shops etc for almost a year, still haven't found a solution. Also posted this another forum but got no replies there

The problem
My problem is a persistent misfire on cyl #5, the higher the boost the more likely it is to happen. It always happens above 6k rpm and only in wot. It always happens on#5

My car
Running 26.5psi
N54 built engine (JE pistons, FCP engineering rods)
Turbos TTE680
Index 12 injectors, new hpfp, walbro 525 lpfp, 3.5bar tmap, everything down to the boost solenoids and vacuum lines is new
Sparkplugs 2 step colder and S55 coils - I ran this boost on this setup with no issues until this problem started

What I already tried
No active codes (except when it happens the misfire code on #5)
No timing corrections prior to the misfire
STFTs, AFRs, looking very healthy
Swapped plugs
Got a new set of plugs
Swapped coils
Checked coil harness to and from the DME
Got new coils
Swapped injectors
Got a new injector with new seal and decoupling element
No injectors have any sign of blowby
Compression test is good on all 6 cyls
No carbon deposits anywhere in the engine is it was rebuilt 15k miles ago
As I've heard that a built engine can have a different sound and trick the knock sensors into registering knock, I've checked the "Desanitize the knock tables" from MHD and yet nothing changed.
Checked the PCV valve (which is upgraded aluminium) - it looks perfect
My mechanic as well as my tuner have ran out of ideas.


I am at a loss of what could be causing this. I cannot think of anything else to test. I would really appreciate some input from you guys as I've been blasting my brains for a year trying to find a solution for this. Thanks.

Have you done a compression test ?
Manual or AT ?

 

[Catalin335xi]

Have you done a compression test ?
Manual or AT ?

Hi and thanks for the reply. I did a compression test, 9bar pretty much all around (the engine being built with forged internals it has 9.5:1 compression ratio compared to 10.2:1 stock so it's a good value). Car has the stock 6speed AT

 

[Krampus]

Bad battery?

 

[Catalin335xi]

Bad battery?

Did not take into consideration this as I thought in WOT the alternator should more than overcome any low battery voltage. But my battery is definitely not healthy as if I sit listening to music for 10mins+ the car won't start afterwards and I had on my todo list a battery but I simply did not consider it a priority until now. Will change it and report back.

 

[wheela]

Did not take into consideration this as I thought in WOT the alternator should more than overcome any low battery voltage. But my battery is definitely not healthy as if I sit listening to music for 10mins+ the car won't start afterwards and I had on my todo list a battery but I simply did not consider it a priority until now. Will change it and report back.

I don't know if it's true, or which models have intelligent dynamics, but a reputable member once posted on here that intelligent dynamics can electronically disengage the alternator during WOT to maximize torque sent to the wheels - so in essence just running off the battery at WOT. Again, I don't know this to be true to a certainty, but thought it was worth mentioning given the context.

 

[Catalin335xi]

If that is the case, I would expect it to throw random misfires, not just on cyl 5. But then again, who knows what cable related to cyl5 is slightly corroded and coupled with the low battery voltage results in a misfire on that cylinder. The battery needed replacing anyway so I'm doing this next.

 

[SLOWESTN54]

I don't know if it's true, or which models have intelligent dynamics, but a reputable member once posted on here that intelligent dynamics can electronically disengage the alternator during WOT to maximize torque sent to the wheels - so in essence just running off the battery at WOT. Again, I don't know this to be true to a certainty, but thought it was worth mentioning given the context.

Isn't that just M cars

 

[pbondar]

Isn't that just M cars

E89s Z4s do that trick

 

[pbondar]

Hi I wonder if it’s TTE that’s the issue…

We have a similar issue on cylinder 6 with TTE500s…similar state of parts save I haven’t rebuilt the whole engine…we are still datalogging to try and find the issue..my tuner (having done the usual replacing parts thing) now suspects it’s an erroneous vibration from another part causing a false triggering ….will advise if we find out

 

[SLOWESTN54]

Do you have a stock DCT flywheel @pbondar

 

[Catalin335xi]

yeah that vibration thing I also suspected. But I think checking the "desanitize the knock tables" in mhd should go around the false vibration causing a misfire? Maybe I am wrong, but that is what I tried and it did not do a difference in my case. Maybe it can do in yours, if you know for sure you don't have a real knock you can try this to rule out a false knock.

 

[SLOWESTN54]

yeah that vibration thing I also suspected. But I think checking the "desanitize the knock tables" in mhd should go around the false vibration causing a misfire? Maybe I am wrong, but that is what I tried and it did not do a difference in my case. Maybe it can do in yours, if you know for sure you don't have a real knock you can try this to rule out a false knock.

Try b58 coils. Fixed my issues

 

[Catalin335xi]

Try b58 coils. Fixed my issues

you had the same issue?

 

[wheela]

yeah that vibration thing I also suspected. But I think checking the "desanitize the knock tables" in mhd should go around the false vibration causing a misfire? Maybe I am wrong, but that is what I tried and it did not do a difference in my case. Maybe it can do in yours, if you know for sure you don't have a real knock you can try this to rule out a false knock.

Misfire and knock are different and detected differently, so I suspect that adjusting the knock tables will have no influence on reported misfires.

 

[wheela]

Isn't that just M cars

Good question, hopefully somebody knows conclusively and can chime in. Sounds like e89's have it - thanks @pbondar !

 

[wheela]

Hi I wonder if it’s TTE that’s the issue…

We have a similar issue on cylinder 6 with TTE500s…similar state of parts save I haven’t rebuilt the whole engine…we are still datalogging to try and find the issue..my tuner (having done the usual replacing parts thing) now suspects it’s an erroneous vibration from another part causing a false triggering ….will advise if we find out

Not to thread jack too much, but are you having timing corrections on 6 or misfires on 6? (Or both?)

 

[Catalin335xi]

Misfire and knock are different and detected differently, so I suspect that adjusting the knock tables will have no influence on reported misfires.

Need to read the manual in this case, to get exactly how the engine registers a misfire. I know what a misfire is, but I assumed that knock sensors played a role in their detection by somehow figuring out that a cylinder "sounded" different to the others so it misfired but probably I am wrong. Thanks for the clarification, will research this further.

 

[pbondar]

Do you have a stock DCT flywheel @pbondar

Yes but I’ve got a new M2/M3 one with fresh bolts sitting on a table ..that hasn’t cured it..maybe I should fit it?

 

[pbondar]

Not to thread jack too much, but are you having timing corrections on 6 or misfires on 6? (Or both?)

The timing corrections bear no resemblance to cylinder 6…it often has the least adjustment…go figure?..no misfires…just shuts cyl 6 around 6.2k…not consistently having reduced boost a small amount…my boost leak stopped play for a while but will now knuckle down to bottom this out…silicon hose connections permitting..