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Discussion Starter · #1 ·
Technical question guys… need some help!

2015 N55 - 40k miles.

Blue smoke coming from exhaust after idling for a few mins. This only occurs when up to temperature, never from cold/if the vehicle has been left for a few days etc.

The smoke ONLY appears when increasing revs/pulling away and doesn’t appear under idle revs. Few blips of throttle and the smoke is ejected/gone. The longer it’s left idling the more smoke appears (but it’s a gradual/proportional increase in volume, not horrendous) and still clears after a couple of revs.

The smoke does not appear, at least not detectable, whilst driving that I can tell (have been followed by a friend). No loss of performance at all.

Have Checked/info:

  • Spark plugs are all in good condition and uniform in appearance.
  • Catless Downpipe removed, appears clean.
  • Exhaust side of turbo appears clean.
  • Inlet side of turbo appears clean.
  • No apparent play in turbo, other than slight wastegate looseness (when cold)
  • Oil drain pipe is free and clear.
  • No error codes.
  • Oil was fine when dropped, nothing obvious.
  • Reverted to Stock Map.

Engine wise the car is running:

  • BM3 Stage 2 (on car for around 3k miles)
  • Decat Downpipe, centre res still fitted.
  • Forge Charge Pipe
  • Forge Turbo - Intercooler pipe
  • Massata HD Intercooler
  • DV+ Diverter Valve
  • AFe Pro DryS

Since noticing smoke I have installed/upgraded:

  • MST Turbo Inlet Pipe
  • MMR N55 Oil Catch Can
  • Changed Oil/Filter (Shell Helix 5w-40 LL04 FS)

Car has regular oil changes (~5k interval) - FBMWSH and is only run on 99oct. Premium unleaded.

The only things springing to mind are:

  • Turbo Oil Seal
  • PCV
  • Valve Stem Seals

The latter (VSS) I feel are less likely due to mileage and uniform spark plugs. AS far as I’m aware it’s also highly uncommon in N55.

Help/opinions/advise greatly appreciated.
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I had a similar issue and it ended up being the VSS.

 

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Discussion Starter · #3 ·
I had a similar issue and it ended up being the VSS.

Thanks for the reply, I actually read yours just prior to posting!

Unless I misconstrued, where mine seems to differ is the smoke doesn’t occur at idle without throttle input, nor do I have any loss in power etc. mine only occurs after a couple of mins idle with throttle input.

If you don’t mind me asking (the worst case being VSS) how much was the rectification and was it possible ‘in car’?

Cheers.
 

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Thanks for the reply, I actually read yours just prior to posting!

Unless I misconstrued, where mine seems to differ is the smoke doesn’t occur at idle without throttle input, nor do I have any loss in power etc. mine only occurs after a couple of mins idle with throttle input.

If you don’t mind me asking (the worst case being VSS) how much was the rectification and was it possible ‘in car’?

Cheers.
I’m also having this and seems to show more when the weather is warm. I have only ever heard of people having this issue when they have a decat downpipe installed, I have also seen people change turbos as that’s what they were diagnosed to be, and it make no difference. I have been in touch with a bmw specialist who also does performance stuff and he said it can be caused by the decat and they can have this effect. I don’t want to go changing and replacing things if it’s just down to a decat.
 

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I’m also having this and seems to show more when the weather is warm. I have only ever heard of people having this issue when they have a decat downpipe installed, I have also seen people change turbos as that’s what they were diagnosed to be, and it make no difference. I have been in touch with a bmw specialist who also does performance stuff and he said it can be caused by the decat and they can have this effect. I don’t want to go changing and replacing things if it’s just down to a decat.
I should mention too I have the exact same as you, leave it for 30sec to idle and it will smoke when throttle input is given. No smoke when driving other than when waiting at lights and setting off occasionally
 

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Discussion Starter · #7 ·
I should mention too I have the exact same as you, leave it for 30sec to idle and it will smoke when throttle input is given. No smoke when driving other than when waiting at lights and setting off occasionally
Hi Owen

On another forums/group - exactly the same post - I’ve had several people point towards Valve Stem Seals as well as LordBass above. I’ve also had acouple point towards turbo.

Verification wise, the methods undertaken so far are consistent with the recommendations I’ve had/the correct route.

In your case I’d for sure check the following items - they’re relatively easy and cheap.

  • Remove and check sparks
  • Remove and check down pipe/exhaust side of turbo
  • Check turbo to Intercooler pipe
  • Check charge pipe

If you remove the turbo you will be able to get a good look into the exhaust ports which should give a good indication on whether the seals have ‘gone’. Plenty of examples online to identify.

How many miles has yours covered etc.?
 

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I think my spark plugs are due to be done, how could this cause the smoking issue though? I have covered 15k miles since owning it but the car is on 60k miles. Was bone stock when I bought it and noticed the smoke as soon as the decat was installed.
 

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id say if you havent already done so then change the PCV/Breather first. This is probably the cheapest/easiest to do. This part really should have a service life as it does tend to clog up and cause all sorts of issues.
 
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id say if you havent already done so then change the PCV/Breather first. This is probably the cheapest/easiest to do. This part really should have a service life as it does tend to clog up and cause all sorts of issues.
PVC valve is built into the rocker cover, rocker cover is an expensive part from BMW. I did do the test of holding a smoke source to the top of the barb fitting on the valve last night. If that sucks in the smoke then supposedly the valve has failed, but it did not.
 

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My 240 is also doing this but it’s only done 6k miles and 70 plate so pretty much new. Started doing it a couple of weeks ago after having its first service from the dealership. I was thinking they may have over filled the engine oil. Anyways phoning them on Monday and they can sort it out.
 
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Discussion Starter · #13 ·
Did anyone get any further with this?

My friends M235i is doing exactly as mentioned by the OP. We're a bit stumped....
In short, not yet.

It is strange, lots of theories. LordBass had similar and it turned out to be Valve Stem Seals.

I’ve been in contact with a few guys in the US where the market is arguably larger. Others have had a combo of Valve Stem Seals AND PCV.

I’ve done the flame test and it does show a very slight suction, but honestly it was hard to tell conclusively- and it doesn’t guarantee it’s fine - it’s a multi faceted system and the flame test only shows a failed diaphragm iirc.

I’ve compared it side by side with a low mileage, well maintained N55 M2 same conditions, same run time etc. Oil cap removal test felt and sounded similar. Mine did pull a flame into the vacuum test port ever so slightly though

In short, the PCV going bad can cause the pressure to rise/spike under idle condition and force oil past a worn (read as: hardened and not necessarily failed) valve stem seals.

Interestingly the Valve Stem Seal cases I’ve discussed with the guys in the US and UK have ALL been 2014-15 well maintained and not stretched out to BMW recommend intervals. Call me synical… but it’s easy to read into that.

Personally, I’m a belt and braces kind of guy, it’s low mileage and immaculate…so I’m going to do both. Valve cover and Valve Stem seals.

FYI an OEM Valve cover is manufactured by Mahle - I’ve been advised, but not personally had hands on - the Elring and Febi Bilstein replacements are excellent quality, indistinguishable in quality from Mahle/BMW OEM.

I’m booked in with a specialist on 17th October. If neither fix it, it only leaves the Turbo.

Feel free to DM me any other questions.
 

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Discussion Starter · #14 ·
I think my spark plugs are due to be done, how could this cause the smoking issue though? I have covered 15k miles since owning it but the car is on 60k miles. Was bone stock when I bought it and noticed the smoke as soon as the decat was installed.
Apologies missed this…

Spark Plugs pulled to look for fouling on the electrode - a sign of oil in combustion chamber. Doesn’t completely rule out Valve Stem Seals, but if black it’s a good indicator that they’re well past their sell by and likely the cause. Doesn’t indicate the health of exhaust Valve Stem Seals - these can leak into the Exhaust Ports and be ignited through turbo/exhaust gasses

PVC valve is built into the rocker cover, rocker cover is an expensive part from BMW. I did do the test of holding a smoke source to the top of the barb fitting on the valve last night. If that sucks in the smoke then supposedly the valve has failed, but it did not.
See reply today - Elring or Febi-Bilstein Units.
They’re on AUTODOC for sub £200 including new seals and bolts (captive). £450-500 for BMW OEM.

Some well respected guys have advised me to avoid the bandaid cut the cap, replace the diaphragm and bond a new cap - this doesn’t fix the whole PCV system, only a damaged main diaphragm - a few YouTube videos about explaining this first hand.

Hope that helps.
 
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