Hey everyone! I've read all the postings I can find on the carbon buildup problem and would like to share my experience and ask for "what would you do" feedback.

2008 MCs 6 spd. bought in '09 with 6,000 miles; strictly a Shell premium gas user; earlier this year, at 25,000 miles started to have a popping sound from the exhaust when letting off the gas to shift up; then, the car started having indigestion at stop signs: you're braking to a stop and the rpms drop to where the car is barely running and feels like it's gonna die.
Local dealer replaced high pressure fuel pump on extended warranty. Did no good; "oh we saw a lot of carbon buildup when you were in before, so you need the shell blasting thing; that will straighten this out." Wrong. Car still making the popping sound, exhaust pipes totally black-black; back to dealer: scope shows nothing wrong and the black pipes are normal; yesterday, needed a burst of speed getting onto the interstate; got the speed, but the car felt like it had passed a rock out its back end and I could see a good amount of black smoke in the rear view mirror. What is my next move? THANKS for any ideas you might have.

 

Hmmm. No warning lights? Has the black smoke continued? Black in the tail pipes is normal for me.

 

So they replaced your fuel pump, and did the walnut blasting? I would say try a different gas station like Sunoco if you live on the east coast check for 94 octane, to clean your fuel system from 93 octane. I'm guessing which state you live in cause I'm on my phone.

Once you do that get a fuel system cleaner and maybe also an oil change. Hope that kinda helps. How long do you normally do your intervals on oil changes? Anywhere from 5-7.5k is good.

 

Black soot on the tailpipes is normal. The MINI runs a hair rich so it's unburnt hydrocarbons.

What do your sparkplugs look like? That could offer some clues.

If you haven't cleaned the carbon out yet it's a good idea to get someone to clear it out or do it yourself.

BTW, even before my ECU tune, I would get some cute burbles from my exhaust during upshifting.

 

Thanks to all for your replies!

Shane, the carbon was blasted out recently and while at the dealer everything checked as in good shape, including the plugs. Agree, the burbles are fine with me too! It's the big belch and black smoke that makes me wonder if we're heading down the road to carbon blasting on a TOO regular basis.

Rob, am in Ohio and don't have Sunoco, but there has to be a station with 94 and I'll try that; although I did run Sea Foam cleaner through the system in the last 6 weeks. Oil changes are within the range you mentioned and just had one 2 weeks ago.

Mini2, no, the black smoke was just right after the bigger pop and what felt like what might have been a blockage blew out the tailpipe. And there have never been any warning lights and the dealer has never been able to find a record of an issue on the 'puter.

Thanks, Steve

 

It could be possible that the catalytic converter might be on it's way out, either in the downpipe or the second one downstream. These cars have very sensitive cats and when the HPFP goes, it's dumping even more un-burned fuel into the exhaust system, and can easily ruin a cat. Maybe start there?

 

Bullet, thanks for the idea. I will check it out. Steve