Help, Random misfire

[Pops848]

I'm hoping someone might be able to help me here

A4, 2.4 V6
I just changed the rocker cover gasket as it was leaking, both sides so two gasket changes
Since then I've had a random misfire code on cylinders 4 and 5
I've put new plus in and swapped leads, misfire stays on 4 and 5

Took it up he motorway and got misfire on all but 6

I assume it's going to be coil packs, but it seems odd that it was working fine and then a rocker cover gasket now causes a misfire, it's very noticeable and is constant
Error codes throw up when driving for a minute.

As I don't think it's leads or plugs my next step will be coils, hoping someone else may have some suggestions?

 

[Retroman]

Vacuum leak from old pipework disrupted during the job? Large MAF bellows on rear left of engine as you look from front - has that split in one of the folds? Also a very common BMW problem.

 

[Pops848]

I'll check the MAF, thanks, I saw one very skinny pipe that went from back of the engine to under the power steering resivoir has snapped, tidied it up and pushed it back into its rubber housing so assuming that's all good

Would a vacuum leak misfire on multiple cylinders?

 

[Retroman]

Logically, it didn’t seem likely that 5 to 6 of your spark plugs or ignition coils or injectors would start to fail and “play-up” immediately after replacing rocker gaskets. Random misfires across most of the cylinders suggests a problem with the fuel/air ratio and an overly lean mix (caused by unmetered air getting into the system) would cause a “lean misfire”. In a crowded engine bay, I could well envisage that rubber vacuum pipework or an electrical socket, could get inadvertently disrupted. PCV pipework can get quite brittle.

 

[Pops848]

Thanks for the reply

I'm guessing I've pinched or ripped a vacuum pipe, difficulty is finding it! Thankfully a kind member on this forum is going to help me with vcds as I have lite version which means I can't look at bank 32, fuel which will help prove if I have a vacuum leak. If I do it's going to be a lot of hunting

 

[Pops848]

found today that the crankcase breather is split and someone wrapped it in gaffa tape, I'm going to replace it but I doubt this would cause a misfire?

 

[QuattroCalum]

found today that the crankcase breather is split and someone wrapped it in gaffa tape, I'm going to replace it but I doubt this would cause a misfire?

On most cars the crankcase breather will eventually join the intake,re introducing unburnt blow by gases to the intake, when there is a split pipe in the PCV system this allows the intake to draw in as much air as it wants. Obviously this skews the fuel mixture resulting in the misfires, hopefully you'll find it, more than likely in a very awkward to get to place, as always.

 

[Pops848]

On most cars the crankcase breather will eventually join the intake,re introducing unburnt blow by gases to the intake, when there is a split pipe in the PCV system this allows the intake to draw in as much air as it wants. Obviously this skews the fuel mixture resulting in the misfires, hopefully you'll find it, more than likely in a very awkward to get to place, as always.

Thanks Calum, for some reason I didn't think the PCV system was as important as other potential Vacuums, more just a way to burn excess oil vapour, reduce emissions etc and the rest of it.
Been looking at this diagram from realoem, very helpful as there seems to be some slightly different parts between a MK1 and MK2 2.4 v6. Mainly cooling and breather hoses.
I'm going to replace or remove the PCV ssytem, parts2, 3, 4, 5 and 6 by the looks of it

 

[Pops848]

FIXED

Coil pack was the culprit

Thanks to all for your help!

 

[QuattroCalum]

FIXED

Coil pack was the culprit

Thanks to all for your help!

Glad you have it sorted, what were the chances?


Sent from my iPhone using Tapatalk

 

[Pops848]

Glad you have it sorted, what were the chances?


Sent from my iPhone using Tapatalk

I know, tell me about it!

I guess I'm kind of lucky in that it's a lot easier to replace the coils than it is the PCV, still going to replace the PCV though as it's going to be a culprit at some point, it's not if, it's when