09 cooper S- misfire -engine design problem?

[petrolblue83911]

Just had to bring my mini to the dealer for an issue where the car has a slight hesitation when accelerating, most noticeable when merging onto the highway/at highway speeds.

They ended up taking the top end off, and cleaning the combustion chambers in a sand blasting cabinet, (using walnut shells) it cost me nothing as it the car is under the mini next warranty but.. the dealer tells me, this is normal for these engines, and be prepared to do this every 20k miles or so...are you kidding me?? they charge 600+ for this service if its not under warranty...

wow.

I have only ever used good quality, premium gas, and the car gets mostly highway mile's, and I while I enjoy driving it I don't abuse it!

I was told that the direct inj. engines "all need this" because carbon builds up on the top of the cylinder heads.

is this true?? -I'm assuming it is common as they actually have built their own setup in the dealership to specifically perform this work. When I got the car back, it was perfect, no more misfire...

how many others have the same issue?? makes me want to ditch the car honestly because this, as well as the insanely fast wearing brake pads make maintenance quite a hassle..

[Dave at Pelican Parts]

It's not in the combustion chambers, it's in the intake ports. On port-injected engines, the ports get sprayed down pretty constantly with fuel. That dissolves any oil that may have gotten in through the PCV system and carries it to be burned in the combustion chamber.

Direct-injected engines don't have fuel in the intake ports. So if any oil vapor gets pulled into the intake, it can deposit on the port walls or the back side of the valves. If it does, then it turns into a nasty-looking black goo that partly blocks the port.

This is relatively common in the DI MINIs. Manufacturers still seem to be figuring out how to deal with the problem in DI cars, primarily with ever-larger oil separators in the PCV system.

Aftermarket catch cans are reputed to help in the case of the MINI. I haven't tried them, so I can't really say myself. And actually, I have a standard Cooper (not an S) which I think still has port injection.

--DD

[petrolblue83911]

Thanks Dave,

That's helpful-

The fix completely solved the issue for me, but the prospect of having to do this repeatedly every 15-20k miles is unfortunate!