Hi All,

I had a good spirited drive on Saturday evening, everything was fine. Woke up Sunday, drove the car and for some reason at lower revs it is stuttering and juddering and the "boost meter" is flitting around... I'm assuming it's more engine than transmission, but the strange thing is there are not fault codes when scanning the ecu. Any ideas? I've only had the car a month or so, hoping its something trivial.

Thanks in advance.

 

The symptoms you describe mostly sound like a worn wet clutch. This is a common issue with these cars. Lots of stop and go, race starts or burn-outs (everything that increases heat) can accelerate the wear. On the other hand it's at least not a major repair.

 

Thanks for this, this is my first automatic transmission and I must admit I am not altogether familiar with how a wet clutch works etc. What would be the expected resolution? is it a complete replacement? just a consumable part of it which needs replacement? or just a transmission service ?
When you say not a major repair, how expensive would you estimate this to be?
P.S - I am still in the first month of my extended warranty, is this likely to be covered? or considered wear and tear?

thanks in advance.

 

Usually it's a complete replacement. I think I've read that it's a repair for about 1000€. Though I would say it should be covered under warranty. I hope it works out for you.

But please keep in mind that this is just a rough diagnosis based on your descriptions. There is still a chance that other things could be the reason for this issue (e.g.: leak in the air intake system or faulty ignition coils).

 

For starters, the transmission in this car is not a normal automatic transmission. A normal automatic transmission has a torque converter between the engine and transmission. This transmission however, similar to a manual transmission, has a computer controlled clutch. More specifically a multiplate wet clutch, as opposed to a single plate dry clutch in a manual transmission. The former operates in an oil bath and has multiple plates and friction discs sandwiched together. This clutch can certainly wear over time, but symptoms are typically that the clutch starts to slip, which manifests itself by the revs climbing without a corresponding forward motion of the car. If you've driven manual transmission, then you are probably familiar with the feel of a slipping clutch. Does it feel like that?

TBH, your description of the issue sounds more like the engine is misfiring, however, one would expect a flashing check engine light at that point.

Perhaps a bit more info on the car would be helpful. What's the model year and mileage? Is it tuned? Foul spark plugs is a common issue of tuned cars for example.

 

The description of the symptoms "at lower revs it is stuttering and juddering and the "boost meter" is flitting around...". Sound exactly like what is happening here in this video:


Afterwards they replace the wet clutch (and also change the transmission oil to keep the new wet clutch from dirty oil) and do another test drive at the end and the issue is gone. OP, I think you can have a look at the video and see, if the symptoms are the same or different.

 

Good find. The video is quite long, so didn't watch it to the end, but watched the test drive part and the boost test showing there's no leak. They were quite stumped as well, and I haven't come across these symptoms either caused by a failing wet clutch, but there we go. Definitely seems exactly like what OP described. I've watched some videos from these guys before. They certainly know what they are doing.

 

Wow, thanks so much for sharing this video... this looks exactly the same problem I am having. Which is unfortunate, as it seems I need a new wet clutch, but hopefully as I have only had the car a few weeks it will be covered under warranty. Thanks everybody so much for the help, I will keep you updated on how things progress.

 

Hi All, Just thought I'd update you all on the progress of this incase anyone is interested and incase it helps anybody in the future.

To cut a long story short, it was a coil pack causing the problem, despit my symptoms being exactly the same as those in the video kindly shared above. £250 sorted.

The longer more unfortunate story, is that during my local mercedes specialist diagnosing this, they updated some software within the car, this has now I believe lost the stage 2 map, which is not great and will cost another £1000 for me to rectify. I am however glad that I do not have an expensive wet clutch to replace..... yet.

My new question - Where do people recommend for remapping/tuning ? Ideally somewhere close to Hertforshire/Essex/Bedfordshire.

 

Misfires as I thought. Strange that you didn't get a flashing check engine light, but maybe the misfires weren't considered severe enough yet. Also, I see the car was tuned, that was perhaps another factor. Sounds like they flashed the ECU, so yes, that wiped out the tune. Question is will the problem come back if you tune it again. It's difficult to clearly say the issue was actually the coil, now that the ECU is back on stock tune. Could as well have been the tune causing the coil to act up. Can't help you with a recommendation in your area and I personally stay away from tuning these cars. But what tune was on there before? If you want the same one back, then perhaps contact the tuner?

 

Indeed, you did call misfires from early on. As you say, I expected some check engine lights if it was a misfire, which is why I went down the other path. BUT after they flashed the ECU, all of the fault codes came through (including ones for the missing cats etc), so it SEEMS as though the tuner had blocked any CEL's from coming through ?? Which seems dangerous. OR something more sinister was done by the previous owner in order to cover issues and sell the car. But essentially the physical coil pack had damage to it, so I am confident that with the coil replaced and a new tune all will be back to normal. The tuner was MSL who I believe are reasonably well respected, but are best part of 3 hours away from me so was just wondering if any better options were more local.

 

That explains the mystery. I probably wouldn't go for a tune that hides error codes that could be important. That's not very confidence inspiring, but it goes to the point why I'm personally staying away from tuning. Running an engine out of spec can come back a bite you.

 

Thanks, @C63-Sam-Everist for reporting back on the issue. Good to know that these symptoms can be caused by both issues and great call by you @superswiss !

 

Glad this was sorted. Coils can be flaky when cold right before a real failure. I think most of us would suggest not having a tune until you figure out all of the details of this car. Especially wait if you think anything was done by shortcut previously. Get a compression and leak down test, drive the car for six months to a year and then get the tune, if you want it.