kevink2

Have you any experience with DI engines?

Intake Valve back side deposites are also a major DI problem ( as well as intake manifold ports) on many cars.

For each cylinder, could you put the intake wide open, the exhaust valve closed, and the piston at TDC, then using a fine grade of shells ( industrial products ), blast the intake valve and combustion chamber with a tube inserted in the intake port, with particles exiting the spark plug hole(s), and possibly the intake port too. ??
Clean out with vacuumed air, and perhaps a solvent chaser?

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MBRedux

Agreed, but I'm not willing to shell out $100K+ to see if they did or not. Until I know for sure, my money is staying in this guys wallet.

MBRedux

Most of our members are strict enthusiasts of our private shop, (& more than half are not Nissan). Of those roughly 40% are DI engines. This is the reason I am so alarmed by this issue. I'm simply amazed that manufacturers thought they could get away with this. But I blame government for placing such high fuel efficiency standards on modern cars, most manufacturers have obviously cut-corners to meet these cafe' standards and still make a profit within their market demographic. It's a crying shame.

To answer your other questions, yes that was the procedure about 25-40 years ago, but no longer today. Most high performance engines, including DI (which isn't really new) have quad valve heads, that is 2 intake and 2 exhaust. Removing the intake manifold exposes only the twin intake pair, not the exhaust. Most spark plugs are crown mounted these days so vertical exiting will not work. The blast tip can be curved to get the back side of both intake valves at the same time. As far as the manifold is concerned, if it needs cleaning, it can be done very easily since it now off the car.

nyca

A cleaning solution injection (not Seafoam), done as part of periodic maintenance, can work. Of course if the condition is allowed to persist for a long period of time, it won't help much. But in an EFI engine, that intake rail is cleaned by the fuel/fuel detergents mixture - so it can be cleaned.

These DI engines are here to stay given the new fuel economy regulations - there is no perfect oil separation unit, so this is life from now on.

MBRedux

Actually not... this is a cutaway of VAG's latest Duel Injector set-up for their new 1.8L EA888 engine series*, which will soon be incorporated all across their Lambo/Audi/Porsche/VW etc. engine line-up. Notice they reinstalled the port fuel injector where it was, thus cleaning the carbon as you drive while keeping the direct injector in its place as well. So it's a "dual injector" set-up. The DI injector kicks in under heavy load only, where it will do the most good... (i.e. better power, cleaner burning and improved fuel economy.). Under light loads the port injector kicks in and cleans off the carbon.!!

I was hoping the Mercedes would have incorporated something like this, but sadly it appears they didn't.... fools.



*We'll see it first in the next generation MkVII Golf/GTI

2012c350

So what's the best way to determine that the carbon buildup is happening? Is the problem that the intake valves won't seal well? If so I suppose doing a compression test on the engine when it's new and then near the end of warranty would be a good enough indicator to decide to pull the intake and look into the head for buildup. Would proof of dropped compression and pictures of the engine with major carbon build-up be enough to force MB to fix this as a warranty item?

And as a follow-up, anyone know enough about these cars/engines to know how difficult it would be to remove the heads with the engine still in the car for a DIY project?

kevink2

There might be a special thin rod borescope that can be past down the spark plug hole when the intake valve is wide open, to view build-up on the back side of the valve head.

The problem is that it is a thick deposit, that restricts flow into the cylinder.

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kevink2

I didn't think that deposits on the back of the exh valve head were a problem with DI or any engine, due to the high temerature it maintains, vs the intake valve. Every old head I pulled (non-DI) had no deposit on the back of the exh valve (especially the ones I polished for my race engine ).

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2012c350

So an air fuel ratio reading / rich condition could be an indicator? Or would the computer just adjust the fuel downward if the carbon buildup causes air restriction? I'm just trying to find out how I can be certain when the problem happens so that I can try to get the dealership to fix it.

kevink2

NO on A/F meter. Many shops have boroscopes now .. best non-invasive way to check.

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MBRedux

This is right... so? I never mentioned that the exhaust valves were the issue.

MBRedux

MBRedux

This will show very little, and like you said, the system will try and compensate to a limit.

Yes, and now they're very inexpensive. COSTCO has a camera probe that's in color with a detachable bluetooth screen for $125 bucks!

2012c350

Thanks for the info. I'll buy a boroscope and will probably get the car dynoed after the engine is broken in so that I have a base. No car, in this day and age, let alone a MB should have this as a concern... If I do end up with the purchase, and have this issue come to fruition, this will be my last MB purchase.

nyca

Interesting thread on another forum about the Audi 3.2L FSI - shocking stuff, photos, owner experiences. If the MB DIs do this, forget it:

http://forums.audiworld.com/showthread.php?t=2817781

MBRedux

I think this thread is interesting as well. The owner of a Direct Injected VW/Audi took pictures of the carbon all over his intake valves at 50,000 miles. He cleaned them and installed a Catch-Can. After 38,000 additional miles, he took some more pictures... NO DIFFERENCE! http://forums.fourtitude.com/showthr...res-Discussion


Bottom line--- Catch-Cans are for suckers and Direct Injected Engines are no sweet angels!

nyca

You read these threads - Audi is in for some serious problems as this problem catches up to more owners as their mileage increases. And what about their certified pre owned cars, coming back with 30K miles and then they turn around and sell them used right around the mileage when these carbon problems are first occurring. They are going to have big problems with that. Mercedes must know what is going on with these Audis.

MBRedux

Agreed, but Audi is right now in some serious doodoo! There are at least three class lawsuits filed, and a judge is now deciding to consolidate them into one or not.

Look at my posts.... Sadly it appears Mercedes may be walking in VAG's (Audi/VW's) footsteps.... There is no technical information available from anywhere to say otherwise.

Glyn M Ruck

The fact that diesel engines from good designers like Benz do not do this tells me that if this does prove to be an issue it is going to be very fuel dependent. SA fuel will only be Euro 4 in a years time. I shall keep my trusty boroscope handy & watch a few cars.

SA & US fuel is similarly crap at the present time.

kevink2

Nice pics. It looks like krap builds up on back of intake valve, then perhaps the rough valve stem reams the valve stem seal, especially with a turbo where the seal is pressed hard against the stem by boost pressure. I say this due to the smooth "lava flow" gunk at the stem to valve head joint area.

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Recognise this guy with the skinny legs?

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MBRedux

That may be so but I fear the worst. Why? These new DI engines are in response to the new Cafe' Fuel Standards imposed by the US-DOT back in 2002-04, then again in 2006-08. Manufacturers had little time to really make this work, to make it fuel efficient to meet these new regulations and bring it in at the right price. GM and Ford had issues early on but claim to have solved them. Toyota developed an entirely new induction and CC venting system along with incorporating advanced new valves & guides to reduce heat & friction thus enabling a better sealing valve guide cap. Audi/VW were in denial for many years as owners kept complaining of reduced engine performance and fuel mileage after a year or two of ownership... well they finally learned their lesson and are promising a dual injected engine line-up starting with the 2013 MY. This is an admittance of guilt IMO and will surly ruin their chances of a win in the courtroom. In the mean time they are still selling these defective engines... so go figure! .... and we own two of them! (GTI and the Q5)

But Mercedes is keeping mum on the topic... taking a wait & see attitude with their fingers crossed behind their backs.... I fear the worst.

Actually the stem seal is not at the bottom of the guide but way up on top where it's not touched by the carbon. It's obviously the poor seal leaking too much oil which would normally be cleaned off by the FI system in a normal PI engine. Some after market guys should improve the seal design for these engines and make some good money!

As a young photojournalist way back when, (and a complete auto racing enthusiast and amateur engine builder at the time) I ran into Mr. Newman many times at Watkins Glen and at Lime Rock once in awhile. (He and Bob Sharp are the ones who got me stuck on Nissan Racing/Nismo and I've never looked back)

Paul was a true gentleman and a regular guy who loved talking cars, racing, and the thrill of life....

.... and a great racer...perfect apex Paul!

kevink2

I guess I just misread your related post, thought it implied there was an issue since you made it a point that you could not access the back of the exh valves with a blaster. My bad.

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kevink2

Agreed. I saw him a few times with Bob Sharp, at Summit Pount Raceway. 1st in a GT2? 280Z type machine, later in a 300Z (TT?) GT1 monster. He rarely made a mistake, but definitly had reliability issues.

I built a "Modified" SCCA D-Production engine for my street Triumph GT-6. Illegal mods included triple 40DCOE webers, custom tuned by me. The compitition manual was written by Eng'g chief Mike Barrett, who later led the Monster Nissans in that wild and open Prototype class that included the unbeatable 2.2L Toyota turbo's managed by Dan Gurney, another great guy to talk with.



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kevink2

I was recently at the philly auto show (a shadow of it's former self) and gauking at a ford 4 banger cutaway, when I noticed a slight Asian gentleman in a suit, gauking at the same engine, but taking copious notes. He had missed the cutaway combustion chamber in the hard to access rear of the display, and I showed him how to climb up to the spot. He was a DI consultant for Ford Engines, stated he knew nothing of carbon problems (doubt it), but I think he was talking about varying rail pressure as part of the injection control, and elimination valve overlap at low rpm to reduce build-up.

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MBRedux

Man, I had my fill with those SD-DCOE Webs in those days, great high end power when they worked.... but what a ***** to tune-up, jet properly.. and synchronizing... damn! Don't get me started with stories about Barrett...

Valve overlap is one great solution that both Ford & GM (as well as BMW) have incorporated with great success... reducing vacuum in the chamber thus reducing "suck down" but as the seals wear out, they will still leak.