My wife's 2007 Mini Cooper S had a CEL on (misfire cylinder 2 on my OBD) so I brought it to a local shop and they replaced a coil pack. The CEL came back on; same code. I replaced all the coil packs (it was due; 78k miles) and the spark plugs; reset the OBD. The CEL came back on. Took it back to the shop and they took off the air intake. It needs the carbon cleaning with the walnut shells ($385). It had the same procedure done by the dealer in October 2014 when the car had 58k on it.

My question is what I can do, if anything, to prevent the carbon buildup?

- It is a stock car except for the K&N CAI. My wife asked me if that could be a factor, but I don't think so...

- Probably should change the oil more often. I do it myself every 7,500 miles. Synthetic with a Wix filter

- One one thread, a few posters recommended driving the car aggressively every once in a while. It is a automatic. My wife drives it like a little old lady and scolds me when I drive it in sport mode and hit the turbo. I am thinking of telling her to just drive in sport mode.

- We buy the high octane gas. My wife goes to the Shell station as some other Mini owner suggested that it was the best gas for the Mini. Does it make a difference?

- Any additive I can add to the gas or oil to prevent carbon buildup?

Thanks in advance.... I'd get rid of this car except it is such a blast to drive and I like the Mini culture... (there is a local group here in NH that organizes a drive to the top of Mt Washington (6k+ elevation) every June).

 

Sounds like you're doing all the right stuff. Sadly, looks like doing the walnut blasting when needed is your best bet..

 

Some believe in the oil catch can OCC, do a search here for the threads, some good info. Sounds like your wife needs a base Cooper and you need to drive the S. The 20k interval seems really soon based on most reports. Could also be that the last clean wasn't done well.

 

Drive it harder , and less frequent quick stops reduces the build to some extent , i don't believe there is a way to get around it completely. From what i have seen after i had mine blasted and drove it longer and more distances, it showed less build up then before. Which was only city driving , short distances. Changing the oil around 5000-7500 here also.

DIY here yourself:

https://www.northamericanmotoring.co...-cleaning.html

 

I'm an internet-warrior-mechanic and my posts reflect my opinions and experience, not all-encompassing final say expertise!!!

I have put a lot of work and research into this issue with the N14. The crankcase ventilation hose that leads to the throttle body, the one on the passenger side, is the culprit. Your engine vents through that hose when the system is under vacuum, and vents through the driver side (into the turbo inlet pipe) under boost. If your wife is daily driving the car it will be under vacuum probably 95% of the time... Depending on the nature of the wife

Some people block off the passenger vent hose, and that will prevent carbon build-up, but it leads to a host of other problems that will eventually do more damage (based on what I have read).

Some brands sell an oil catch can kit that filters the driver (boost) side vent hose, but my experience with a name-brand kit lead me to the conclusion that it is not a cost-effective preventative measure. I installed it when I had the walnut blasting done at the dealership, and within 8k miles the build-up was evident again.

I have now modified the mount for the oil catch can to filter the passenger (vacuum) vent hose and it has been very effective.

I've spoken with both Jerry at NM and Aaric at JMTC on this subject. The conclusion that I reached is that utilizing an oil catch can to filter the passenger side (vacuum) crank case vent hose is the most effective preventative measure, but nothing will stop the carbon build-up completely, except venting to atmosphere and plugging the throttle body which is in my opinion irresponsible and certainly illegal, as it leaves that oil on the road now instead of burning it.

Obviously two catch cans, one for each vent hose, is the MOST effective (legal) preventative measure, but that is expensive and can be a challenge to fit under the hood.

Looking at it logically, the passenger vent hose leads to the throttle body > intake manifold > intake ports/valves. That is where the build up occurs.

The driver side vent hose leads to turbo inlet pipe > turbo > "hot-side" intercooler pipe > intercooler > "cold-side" intercooler pipe > throttle body > intake manifold > intake ports/valves. That oil does not make it that far, at least it didn't in my car. This makes a catch can on that side seem unreasonable as a preventative measure for carbon build up. I'm not saying it is not beneficial in other aspects, just not for this specific issue. My "hot-side" intercooler pipe had only the slightest hint of residue after 50k miles, and my turbo is in great shape. I feel safe without an oil catch can filtering this hose.

The bottom line: the issue costs time and money no matter what approach you take. Hopefully what I have shared will help you spend less of each!

 

To stop carbon issues.... you have a few options...
1) park the car....don't drive
2) use water meth injection or pure methanol....and since you drive so gingerly, it would likly never activate....so it might do nothing in your case....and it is pretty $$, but if you think the car is fast now....just wait...lol

Other methods....driving harder, etc are just ways that MIGHT DELAY the next cleaning....

The reality is, nobody has found a perfect way to avoid issues, and due to the motor desgin, they never will...to remedy the issue, mini added valve timing to the other set of valves, and created the n18, then tweaked the software many times.....Carbon still happens, but not as fast....
So IMO, save your $$, and budget to have the Canon cleaning done every 40,000 miles or so....if done at a good independent shop,it's not a HUGE cost....just another reoccuring expense like tires or brakes.

 

Try going back to a non oil air filter. I've had lots of K & N's and they all shed the oil somewhere! In a turbo it mainly gets caught up in the intercooler first but can get all the way down to the engine if the filter is over oiled. On my normally aspirated motors I noticed that my motor oil would get dark very quickly. Once I took out the oiled air filter the motor oil would stay clean looking for several thousand more kilometers.

 

Not sure if I'm reading this right, but did you actually run without an oil filter?

 

No sorry, I was referring to taking out the oiled air filter (K & N). I edited my post to make it clearer.

 

Suggestion....with a gen2 mini, NEVER USE AN OILED FILTER....get a dry filter, or even a paper one ...
The sensors in the intake track can be destroyed by the thin film of oil that commonly ends up in the intake track when an oiled filter is used.

 

Seems like the cold weather intakes are the best bet to reduce carbon, (you will never be able to completely eliminate carbon build up, just a by-product of direct injection), in easy terms, the route for the crank vapors is shorter from the valve cover to the intake valves, causing reduced carbon buildup (somewhat like what was done to the N18, and they rarely have any carbon issues), call your dealer and ask about the cold weather intake manifold,... I have seen very little carbon build up on cars with it,... I am not sold on the catch cans yet, I have seen many cons as far as intake leaks, and I like an unmolested engine bay (purist) but you can try. On a side note, make sure you are using factory (beru,NGK) spark plugs from the dealer, too many issues with stumble and loss of power with other brands/types of spark plugs. coils are the same way

 

Some people have tried the cold weather as it puts the PCV closer to the inlets. I have not heard any very long term test yet.

https://www.northamericanmotoring.co...different.html 11614584240.

 

Well, we had the walnut shell carbon blasting done and the check engine light came back on.... the car is back at the shop for more diagnosis...

 

What are the symptoms? Dealership told me it needed to be carbon blasted and that the timing chain and tensioner needed replacing, but my problem turned out to be the failing high pressure fuel pump. The dealerships diagnosis was still correct unfortunately, just not complete.