MDMercedesGuy

Tonight I was on I-95 and moved out into the left lane to get around someone puttering along - needless to say I floored it to get back with the flow of traffic. After about 2 seconds, my car lost power and started stumbling with a solid check engine light. After I limped it off of the road, barely able to run 50 MPH (not fun crossing 6 lanes of traffic) and restarted it, the CEL went out and it seemed to run fine. If anything, it almost felt smoother.

Fast forward 50 miles on my return trip, and coming around a ramp merging into the left hand side of I-95, I accelerated with 3/4 throttle or so only to be met with another CEL and shuddering. After getting off the highway and restarting again, the car seems to be running fine but I now have a CEL that's on solid.

Now the kicker - I leave for a trip tomorrow straight from work (which is fortunately now right down the street from my dealer) - I'm trying to see if I can get it in for service first thing in the AM to at least diagnose the damn thing. The last thing I want is to be stuck at my campground in rural West Virginia with a dead Mercedes...

Does this sound like the car is going into overboost or does it sound like something else? It's been raining here all day, but I would think if it were misfiring from a bad coil or such I would be getting a flashing CEL. For those of you who have had this happen - does the car run smooth but with less power, or does it shudder like it is misfiring when you put it under load?

MDMercedesGuy

Just got a call to come pick my car up.

Diagnosis: Cylinder 4's coil was loose and not making a solid connection. Additionally, the spark plug in cylinder 4 had a really wide gap - they think it has been that way from day 1.

LILBENZ230

Pleased it was simple. That kind of reaction from a car as new as yours is quite unexpected and alarming, I'd imagine.

Glyn M Ruck

Fortunately a very minor glitch!

MDMercedesGuy

Well, maybe it wasn't fixed. Trying to accelerate into a gap in traffic from a merge ramp Tuesday night only to be met by another solid CEL, stumbling miss and complete lack of power. After getting off of the road and restarting, everything seems normal. I'm not happy at the moment - I didn't spend $45k to not be able to accelerate when I need to. I dropped it at the dealer this morning, after contemplating lighting it on fire and driving it through the showroom window.

I'm in a 2013 C300 Lux in the meantime (interesting car - definitely rides much softer than my car). Contemplating moving to an E250 in the spring - I've decided that I don't want to own this car outside of warranty. I've got some time (18K miles and 2.5 years left) unless it decides to get me killed in the meantime.

Interestingly enough, and something I did not put in the original post in this thread is that it was raining pretty hard when this happened in June. It was also raining when it threw its latest fit on Tuesday. Maybe there is a connection?

MDMercedesGuy

They must have ESP. I made that post and my phone rang.

Apparently it was a single misfire event that caused this time. They don't know what to make of it - they asked about the gas I buy. The station I use frequently happens to be from a station that literally shares their parking lot, so they don't think that is the cause. Apparently they have seen some ethanol issues with these cars if they sit for a bit.

They did a compression test, all was well. There was yet another software update out that they applied. They ran a boroscope into the cylinders and everything looks perfect. They looked at the intake, backside of the valves and such - no deposits (should be good to hear for those who are concerned with DI sludge or buildup), replaced the plugs and want me to drive it. My SA asked me to drop it off sometime when it is raining so they can take it out and try to make it act up. In the meantime, they are scratching their heads.

Glyn M Ruck

A single misfire event. That has got to be the worst of all to diagnose. When you look for it it's long gone.

It could be as simple as a minor localised phase separation of alcohol laced fuel with a little too much water in it.

We had a problem in Brazil many years back with VW Santana's (Passat) with Pierburg carburettors (pre all zinc body) where the engine would stumble/hesitate through the rev range & corrode the carb body below the venturi. After much head scratching & fitting thermocouples all over the engine we found that in certain conditions the temperature was hitting minus 4 degrees celcius below the venturi & causing a separation of hydrous alcohol.

It was hard to credit in such hot surroundings but true & accurately measured.

Good luck!

MDMercedesGuy

Glyn,

I sat down with my SA and talked for a couple about this, and you hit the nail on the head with what they think is happening with my car (ethanol separation). I'm just surprised it isn't more widespread if that is the case. If there ever were a case for more people moving to Diesel in the US, it would be Ethanol, IMO.

I'm a bit curious about all of these SW updates that are coming out for the M271 - it makes me wonder if they are fighting with it to get it to behave with our fuel. I saw a definite decrease in fuel economy after the update they put on last month, and with about 200 miles worth of driving this weekend after picking my car up, it has improved quite a bit.

Of course we've switched to winter gas around here, so my fuel economy went to hell for the season already though...

Glyn M Ruck

While the problem might be peculiar to the car try filling up at a different high thruput gas station for a while. The guys at your normal station might be careless with their water bottoms on their tanks.

The alcohol will of course vacuum it up over time but this might be the very issue you are having. It's worth a try.

I've had to live with alcohol in fuel issues for much of my career. Started in SA when Sasol could not find a lucrative offtake for all the heavy alcohol they produce & dumped it in our fuel. Then when I went international countries like Brazil were running vehicles on up to 100% hydrous & anhydrous alcohols. It's not plain sailing.

The Brazilians are prepared to put up with driveability issues that would drive you & I mad. This has steadily improved as the OEM's have learned to cope with alcohols & oilco's have learned how to blend for better driveability.