Good read about Direct Injection - Mercedes Benz SLK Forum

SLK R172 General Discussion Discussion regarding the Mercedes SLK R172

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#1 Old 03-20-2019
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Lightbulb Good read about Direct Injection

https://www.underhoodservice.com/gdi...intake-valves/
The R172 is a direct injected engine.
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#2 Old 03-20-2019
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Technically R172 is the platform which you can get with DFI engines.

While a real problem for VW and other makes this is not an issue for MB.
They actually acknowledged the potential for the problem and did some engineering to prevent it. (This is why MB was later to market with DFI)

For this one just be glad you got an MB!
(Just remember to use top tier detergent fuel)
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#3 Old 03-20-2019
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How did they solve the problem? My car is having a leaky injector replaced as we speak. It fouled the number five cylinder spark plug, when the local yokel pulled the plug he told me that it was filled with oil. Shipped it up to a real expert and they told me it was a leaking injector. My concern is did the leaking fuel over the course of time cause a carbon buildup on the intake valves?
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Short answer is no, fuel actually cleans up carbon and also on a DFI the injector is after the intake valve.

MB DFI engines are designed with multiple measures to address carbon buildup. These include injector spray pattern, intentional valve timing overlap and PCV treatment.
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Do note that a real concern with a leaking injector is terminal engine damage due to washing of the oil coat on the cylinder wall. This will lead to wall scoring reducing compression I that cylinder.

How long did you drive with the problem?
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It might’ve been as long as 2000 miles. It wasn’t a terribly bad leak, just bad enough. They did do a compression check, and told me the compression is perfect.
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That is a bit long but if compression is good you should be in the clear.
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#8 Old 1 Week Ago
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Well, the demon has once again reared it’s ugly head. I got a CEL, out came the code scanner - same cylinder misfire. The car also burned a quart of oil in about 1400 miles. I just ran the car back 100 miles to the dealership, they can’t get to it until this Friday. I am glad I have an extended warranty.
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#9 Old 1 Week Ago
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All your problems make me worry Mensra. But it doesnt seem a lot of other R172 55 owners are having the same issue so hopefully it is just a rare problem.

I love the car so much though that short of something catastrophic I'll probably pony up for any and all repairs over the years.

How many miles do you have on yours?
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Now you know why I have given my car the name it has. I have a bit over 45,000 miles, I got the car with about 33,000 in November 2017.
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Got mine with 27k on it last month and drove it from Chicago to Danvill KY, then from there home to TX with zero issues and no oil burned during nearly 2k miles driven. Hoping it continues to be steady for me.

I dont think the previous owner was putting the best gas in it though. I noticed a sweetish smell on startup the first few weeks running shell gasoline in it which has since faded. I am guessing the higher detergent levels were cleaning out the engine from some bargai shopper fuel, even if it was 92-93 octane. I read something recently with an independent test showing that shell does in fsct have a higher % of detergents than competing brands (Chevron came in 2nd).

I plan on using my wife's C300 as my daily driver as soon as finances allow fpr the purchase her "dream" (a toyota 4runner) so I can keep Stormy low mileage. Sure wish she'd told me before I spent 33k on a Mercedes sedan; a decent 4 runner isnt much more than that!
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#12 Old 1 Week Ago
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It may have been posted before but here is a good read about the M152 engine which powers our R172 SLK55's. There are some impressive facts including in the Efficiency Paragraph "No other petrol engine features direct injection at a pressure of 200bar, spray-guided combustion...…." etc.
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