Mang0

I've done some cursory searches of the website and haven't found anyone talking about loss of power WITH the boost gauge registering full boost (literally pinging off the right side) at about half throttle in Comfort mode, on a slight incline, only when the engine/transmission are cold.

If I put the car into Sport+ mode and shift manually the "hesitation" and seeming lack of power disappear. I haven't tried Sports or Eco mode when this happens. Throwing no codes (soft or otherwise, scanned by the dealership). Anyone have any ideas?

Car has less than 12,500 miles on it. Could this be perhaps bad gas and the car is knocking? Unfortunately this happened now two days in a row, about the same point in my drive both time-wise, temperature-wise and approximate acceleration habits.

Thanks. New to the forums, my first Mercedes. Don't go easy on me especially since I can't spell 'gauge'.

C43HeartBoost

I think more information is needed. What gear were you in and at what speed when this happened? Is the car new to you, or have you had it for the whole 12500 miles?

Without knowing more it sounds like you were in comfort mode at a relatively high gear but low speed but you did not give it enough throttle for the transmission to kick down to a far lower gear. I have found these cars to significantly lag/bog in comfort mode when cruising around 40-50 mph (usually in 9th gear at that speed in comfort if cruising) - especially when the engine is not warmed up.

Go out and drive in Sport+ at that same speed and see if it happens again (should be 5th or 6th gear at that speed). Also, manually down shifting (or double tapping down shift) is your friend to stay in the correct gear/powerband.

Mang0

Hey there thanks for responding so quickly. This is generally in the 30-60 kph in a light to medium application of the throttle. I have tried pinning it when this happens in the same mode and the car seemingly stands still. Especially with the boost gauge jumping around like it has ADHD under load or not it makes me question things.

The engine and transmission are quite cold at the point this is happening. When I go into sport + when encountering the problem the car is snappy and responsive.

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C43HeartBoost

Ok. In my opinion, this is not a power loss issue - but a drive mode/powerband issue.

Mang0

I got lucky and the dealership was able to replicate the issue. It appears that it wasn't throwing any codes (soft or otherwise) but they looked into it further and are replacing the plugs and injectors. I am not sure why either of these wouldn't be throwing a code but this would also explain why my fuel mileage seemed to be somewhat crappy lately (wasn't enough of a trend to be worth mentioning as I was mostly in sport + the last few days).

Fingers crossed this was it but being less than 3 years old with such low mileage I'm a bit surprised. They had also mentioned they found a 'significant amount of communication errors' whatever that means?

I've never modified the car.

Edit: oh and for the record, I was with you, it seemed like a logic or mode issue.

stockbmw

Was thinking turbo boost leak but good that your dealer is cooperating with you and getting a free tune up as well. Make sure you are getting a brand new plugs and injectors, not them sandblasting the plugs at back or running cleaners through the injectors.

Mang0

I'm so bad at replying. Unfortunately I'm at the mercy of MB warranty mafia, they deemed what should be fixed and what shouldn't. What's worrysome is that they noted one that didn't quite meet guidelines for needing to be replaced so they just popped it back in and now I'm facing _similar_ problems_ , here '17 C43 poor performance/sputtering issues in Northern climate - MBWorld.org Forums

Mang0

Just thought I'd post that I am still experiencing these issues. The dealership's most advanced tech (in age, and knowledge) took the car for a spin with active datalogging and said he didn't see any parameters out of the "norm". He also went for a test drive wth me to see what I was talking about. He acknowledged the issue but point back to everything being within acceptable range, despite the tech stating the car smells like it runs rich, which is why the first fix for this was replacing some fouled coil pack units. This is after them having drilled holes in my exhaust (twice) insisting that the issue was related to freezing up of liquid in the exhaust when the car sits. They pointed to my short commutes as the reason for this icing up which I find hard to believe. It's stored in a non-heated but insulated garage in Northern Canada, and then stored outside at work.

Super important to note this only happens when it gets below -15C. It honestly feels like a vacuum or boost leak. I've tuned enough cars to know when something is out of whack. Is it possible that even with a vacuum leak that this wouldn't be picked up by datalogging tools?

Anything I can do to troubleshoot this? I really am worried about this "pinging" or "overboost" in these cold situations and this does occur even when rad/oil temps are in the middle/operating range which when I step on it, it'll putt and fart around; an unsafe situation trying to get up to speed on a highway/freeway.

W205C43PFL

Personally never have such issue, also live in Canada, temperatures sometimes reaches -20 C where I live. I have a sedan though but also a 2017, hopefully someone else can chime in and help out. Confirming never had this issue bought this vehicle new with below 90 KMs on the ODO. Best of luck fixing this OP and hope it comes sooner rather than later.

jonathan358

I know exactly what you're talking about. I believe this has to do with the crappy PCV system on our cars that fail right at the end of warranty. The oil separator is likely clogged (diaphragm valve/o-ring has disintegrated) and blowback is mixing with oil in the crankcase and going back up to your intakes. This causes pulses in your flow which is what I think causes the fluctuation in the boost reading. Of course this is all speculative, but I have done some research and this seems to be the most likely culprit. Looks like we have a lot of the same issues with our cars lol!

W205C43PFL

Thanks for chiming in, sorry to hear about that.