BMW N54 twin turbos were bad for carbon build up requiring walnut blasting at about 80k miles. They also went through 11 or 12 injector revisions and a few high pressure fuel pumps before they got it right.
The N55 that succeed the N54 has had way fewer issues. Mine has done 100k miles and drives like new with great fuel economy and responsiveness.
CAinCA said:Pete. (l33t FS) said:In reply to Opti :
i wonder what people are doing with the TFSI engines that aren't having issues that is different from the ones that are.
From my post above: "On the GTIs for example they say you can avoid it by periodically driving the car above 3000 rpm for at least an hour at a time." I believe this recommendation came from VW USA.
So the problem is the ridiculously overtall transmission gearing? 
I lived at least 80k miles with a VW that cruised at 4000rpm, world didn't end. I don't get the fascination with running the engine as slowly as possible.
That said, the 2 liter that I had apart, and was fairly clean inside, was in an automatic A4. I don't think they spent a lot of time over 3000rpm, if any at all.
I don't get the fascination with running the engine as slowly as possible.
Nor do I. I've spent most of my life at 4000 and above, even with V8's
Pete. (l33t FS) said:CAinCA said:Pete. (l33t FS) said:In reply to Opti :
i wonder what people are doing with the TFSI engines that aren't having issues that is different from the ones that are.
From my post above: "On the GTIs for example they say you can avoid it by periodically driving the car above 3000 rpm for at least an hour at a time." I believe this recommendation came from VW USA.
So the problem is the ridiculously overtall transmission gearing?
I lived at least 80k miles with a VW that cruised at 4000rpm, world didn't end. I don't get the fascination with running the engine as slowly as possible.
That said, the 2 liter that I had apart, and was fairly clean inside, was in an automatic A4. I don't think they spent a lot of time over 3000rpm, if any at all.
If I had to guess I'd say it's probably more common on DSG equipped cars than manuals. In it's stock form the DSG actively tries to get into 6th gear as much as possible. Unless you're doing 80+ mph on the freeway you're going to be spending most of your time under 3000 rpm. The best upgrade I made to my GTI was a DSG tune.
CAinCA said:Carbon build up is a thing. On the GTIs for example they say you can avoid it by periodically driving the car above 3000 rpm for at least an hour at time.
This is a wivestale from my direct experience with my 2011 GTI that I bought new. I drove the snot out of it yet it still required an intake valve manual cleaning at 50k miles, and was ready for another at 95k miles when I finally sold it. Other than that, the DI system worked fine during my ownership.
In reply to Pete. (l33t FS) :
Nothing wrong with revving the snot out of an engine that's happy to do it. But if the car is going to spend hours on the highway, a slower turning, torquey engine is usually more relaxing to drive (easier to keep quiet / smooth). Just don't gear the thing tall enough that it needs to downshift to climb a small hill, as that breaks every bit of the smoothness you gain. Plus, up to a point, taller gearing = better mpg on the highway.
I think DI engines are just going to need that extra maintenance in there for a top engine clean. It's not hard. Think of this replacing the need to change plugs and wires on older cars.
In reply to Mr. Peabody :
My P71 and the Fusion 2.5 that replaced it shift at about 4K but are geared to fall back to about 2K when cruising. It appears they do that to keep the transmission in its topmost gear until you have slowed to almost 35 MPH, no matter the reason. Another thing manufacturers do to lower emissions?
In reply to Carsandbikes :
Fuel economy. By the time the shift pattern matters, the emissions are very sorted out and are easily controlled.
R56 MINIs have issues with carbon buildup too. I think its recommended to do walnut blasting on the valves every 50-70K miles. I bought my car with 90K and it seems ok but I am looking to do it sometime this summer along with a bunch of other maintenance. The earlier R53 had port injection and didn't have these issues. I want to say that the newer F56 MINIs have revised PCV systems that reduce the amouont of carbon buildup with their DI engines. Some say oil catch cans work but I think I agree with the above re: quality synthetic oils and much shorter OCI to control the carbon.
EDIT: I've also heard from other that being heavy on the throttle helps with carbon buildup, much like what was said above regarding the VWs. I'm always happy to oblige with that one.
145k on the Cruze, 120k on the Focus, 45k on the HRV and 3k on the Silverado comes out to about 313,000 miles in my DI cars. Never had a single issue with any of them related to carbon or fuel system. The Cruze has eaten three valve covers due to the unserviceable PCV system that fails to atmosphere causing a whistle and a CEL.
alfadriver said:Yup, the PFI injector is 90% emissions, 10% power (some may remember that DI injection systems are volume limited....) While I can't be specific, the combination of PFI, and multiple DI injections do wonders for the cold start emissions. But thanks for posting that- spot on.
Very neat! So are the cold start schemes basically using the PFI to create a stratified charge and the DI to create a richer ignition pocket?
I had to clean the carbon on intake valves on my Speed3 at 80k. I was getting random misfire and cylinder 4 misfire codes. PITA job even blasting with walnut shells. I put a catch can in afterwards. I've heard that the second gen Speed valve cover offers better crankcase ventilation and is a swap to the first gen.
In reply to sobe_death :
Uses all of the injections to get a specific mixture.
My daughter called me as a sanity check after the dealer told her that the valves on her Mini needed walnut blasting at 40k-some miles. I thought it was nuts until I googled it. Walnut blasting really is a thing - who knew?
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