[magsmagsmags]

Hi folks,

Trying to fix a cylinder 3 misfire.

Car is a 2008 335i E93 N54. Recent service in my ownership, new plugs, coolant, rocker cover gasket, oil filter housing. Running MHD Stage 1+ with FMIC, Secondary Cat Delete and Dual Intake.

So far i have replaced the ignition coil and tried swapping coils to see if the fault follows, plugs are all new too. I have pulled out the DME to test the MOSFETs for contuniuity and all test OK. My DME is a DME81 and not the 80 which is known to blow MOSFETs so i think its fair to say that's ruled out.

I am showing fault codes for:
29CF - Combustion misfires, cylinder 3
29D9 - Misfire at low tank fill level
2C3F - O2 Sensor before catalytic converter (am aware of this, and have a new sensor to go on, but this never caused issues before - the misfire is new)
2E1A - Firing, Cylinder 3

The car runs lumpy on start up with a slight misfire. Driving cold it hesitates a little bit and splutters occasionally but then is fine. However after a heavy foot, or if i turn it off (e.g. to go into a shop for a few mins) and return, a permanent misfire occurs and won't go away until the car is left for a while.

The DME is out at the moment, but will put it back in later and flash it back to a stock map for the moment.

From asking elsewhere it seems the low fill tank code is common with injector failure - but no experience to vouch for this.

Is there any way to see if it is the injector without pulling it apart? MHD logs?

Thanks

[relative4]

Just swap injectors with another cylinder already, it's not hard.

[magsmagsmags]

I would like to say i'll give that a try... but i am now baffled.

I put the DME back in earlier - fired it up, started fine. Let it idle for a bit and was still lumpy but otherwise as it was.

I thought i'd try flashing back the stock map on MHD as i will need to drive it to the garage at some point. Flashed it back to map 0 (stock) and fired it up and its misfiring horribly right from startup. The engine light started flashing and now i am getting codes for cylinders 4,5 and 6.

I tried writing Stage 1 to see if it helped, but it's the same.

I am wondering if maybe (possibly as well as) the cylinder 3 issue, there might be a fuel issue. I only have 40~ miles in the tank currently.

Any ideas?

[magsmagsmags]

So by coincidence the crank case breather had split which would explain the 456 misfires. Will get another ordered then resume diagnosing the cylinder 3 misfire

[dpaul]

Originally Posted by magsmagsmags

So by coincidence the crank case breather had split which would explain the 456 misfires. Will get another ordered then resume diagnosing the cylinder 3 misfire

Crankcase breather split? I assume you mean the vent hose that goes from the valve cover through a flapper valve to the air inlet duct for the rear (bank 2, cyl 4-5-6) turbo.

A break in that hose will not cause a disturbance specific to bank 2. It is not responsible for your new misfires, particularly at idle with a cold engine.

The obvious suspects are the injectors, which can stick open or stick closed. Rough idle on startup of cold engine is a classic symptom of leaking injectors which are very easy to diagnose. Let the engine sit overnight and get fully cold. Pull the plugs and see of they are wet with fuel.

[magsmagsmags]

Ah. Bugger. Was happy I’d found the culprit.

I don’t have the tool for the plugs annoyingly. I’ll trt and get hold of one.

It just seems really odd a whole bank would fail when literally minutes before they were fine. I’ve never had any codes or issues with anything other than 3

[magsmagsmags]

I did a quick log while stationary today, as well as have a poke around at anything obvious with no luck.

Can anyone glean anything useful from the logs? If not, what else do i need to enable?

https://datazap.me/u/magsmagsmags/lo...?log=0&data=16

Thanks!

[dpaul]

This is very abnormal. Look at your AFRs - bank 1 is steady (and roughly normal for idle) but bank 2 goes all over the place. You also have a crazy short term trim on bank 2, flipping from normal to max (+34) then back again.

I think this underlies the bank 2 (4-5-6) misfires but it does not single out one component for the fault. Most likely, either your bank 2 pre-cat sensor is bad, or the wiring connection from the sensor to the DME is bad or the DME itself is at fault.

Since all this occurred shortly after you re-installed the DME, I suspect you have bent a pin or something didn't seat correctly. But you cannot rule out the possibility that bad injectors are responsible for all your issues.

Have you read the codes again since the 4-5-6 misfires began? Read them and then for the hell of it, reset the lambda adaptations

[magsmagsmags]

This is very abnormal. Look at your AFRs - bank 1 is steady (and roughly normal for idle) but bank 2 goes all over the place. You also have a crazy short term trim on bank 2, flipping from normal to max (+34) then back again.

- You're not wrong! They're all over the place.

I think this underlies the bank 2 (4-5-6) misfires but it does not single out one component for the fault. Most likely, either your bank 2 pre-cat sensor is bad, or the wiring connection from the sensor to the DME is bad or the DME itself is at fault.

- This is why i'm baffled - I know the bank 1 pre-cat sensor is bad and needs replacing, but yet bank 1 seems fine.

Since all this occurred shortly after you re-installed the DME, I suspect you have bent a pin or something didn't seat correctly. But you cannot rule out the possibility that bad injectors are responsible for all your issues.

- I keep thinking this. But the fact i re-installed it, ran the car and it was fine (still idled a bit rough on a cold start, but only the bank 1 pre-cat o2 sensor code was showing) leads me to believe otherwise. I know you're just trying to help but i cannot understand how anything could have changed. I didn't even get out of the car between it idling fine and writing the map to upset anything. I was super careful with the DME and have pulled the cover off today to check for any bent/split wires etc. and all seems well.

Have you read the codes again since the 4-5-6 misfires began? Read them and then for the hell of it, reset the lambda adaptations

-multiple times! Same every time. I've reset all adaptions several times with no joy. I tried unplugging the pre-o2 cat sensor plug on the intake manifold today but that made no difference. Is there any other logs i can do that might help narrow it down?

Thanks for your help btw - appreciate any i can get atm

[dpaul]

Did you remove the DME connectors? You are looking for pins in the connectors that have either been bent or pushed back into their housing so they no longer make a good connection.

As for further logging, I can't imagine how you can even drive this car. I wouldn't.

Actually, you haven't reported all the current codes. You only reported the codes prior to onset of bank 2 troubles

Final thought, map 0 isn't stock - the calibration code is stock but the program codes still contains MHD modifications. Try flashing back to OEM stock.

[magsmagsmags]

Thanks again for the reply.

Yes I did remove the DME and connections. Battery was disconnected throughout. But Makes sense. I’ll pull it again tomorrow and check the pins. It just seems strange it was fine even after it went back in but I guess all it takes is a tiny vibration to break contact if one was bent - stranger things have happened.

I’ll check tomorrow and try flashing back fully to stock and see where we are. Thanks!

[magsmagsmags]

Sorry forgot to post the new codes

They are...

29CC: Combustion misfire, several cylinders
29D0: Combustion misfire, cylinder 4
29D1: Combustion misfire, cylinder 5
29D2: Combustion misfire, cylinder 6
29D9: Misfire at low tank fill level
2C3F: Oxygen sensor before catalytic converter (this is the code for bank 1)

[dpaul]

Originally Posted by magsmagsmags

Sorry forgot to post the new codes

They are...

29CC: Combustion misfire, several cylinders
29D0: Combustion misfire, cylinder 4
29D1: Combustion misfire, cylinder 5
29D2: Combustion misfire, cylinder 6
29D9: Misfire at low tank fill level
2C3F: Oxygen sensor before catalytic converter (this is the code for bank 1)

So you are no longer getting 29CF and 2E1A? Is you tank fuel level low or not?

[magsmagsmags]

Not currently no however they only used to come after driving, not idle. But as it’s misfiring on 3 cylinders I haven’t been able to drive it.

It is low but not absurdly. I am now going to fill my can up and stick 20L in and see if it’s the low fuel issue. Apparently it’s quite common (although seems like a massive design flaw!)

Will update after refuelling

[magsmagsmags]

Cleared codes, refuelled (to half a tank) and ran again. Still no joy so it’s not due to low fuel.

Not been able to pull the DME yet as it’s been raining and don’t want to risk it getting wet

I am now showing just the below codes
2A2C: Mixture control 2
2C3F: oxygen sensor before catalytic converters

I’m sure if I left it to idle long enough I’d throw codes for 4,5 and 6 again but didn’t want to damage anything so shut it off fairly quickly

[magsmagsmags]

Update: Pulled the DME again today - no bent pins, none pushed back.
Also replaced the split PCV valve

No improvements, still misfiring and same codes as above.

[edirty9_]

You ever get this issue figured out? I’m in the same situation. Going to check mosfets next

[Saif2018]

Originally Posted by magsmagsmags

Cleared codes, refuelled (to half a tank) and ran again. Still no joy so it’s not due to low fuel.

Not been able to pull the DME yet as it’s been raining and don’t want to risk it getting wet

I am now showing just the below codes
2A2C: Mixture control 2
2C3F: oxygen sensor before catalytic converters

I’m sure if I left it to idle long enough I’d throw codes for 4,5 and 6 again but didn’t want to damage anything so shut it off fairly quickly

Ha you replaced the O2 sensors yet?

If you haven't I suggest you do so first.

[Jason2130]

On my n54 I got constant misfire on cylinder 3 while car idle but it drive fine and make boost I did a compression it was good, swap coils and plugs swap injectors also walnut blast, put in multiple msd81 still come back has any had this problem

[gogaalt]

did you ever figure out what was the issue?