400d OM656 Turbo issue (E400d All Terrain 2019)

[MeanRedSpider]

Posting here in hope of helping others as it has been a long and painful journey for me.

I have a 2019 E400d All Terrain - very rare car in the UK. It runs what I believe is the OM656 engine with supercharger and turbo. I bought it to tow my race car around the UK from Scotland where I’m based. From the outset (it was 2.5 years old when I got it), I’d get transmission judder on gear changes on longer (2 hour plus) journeys.

At first diagnosis focused on the gearbox but that didn’t improve things. Then they started finding issues with the turbo - eventually diagnosing the actuator sticking. That was replaced, as was the vacuum pipe, and suddenly the car was transformed: delivering the 235bhp and, more importantly, 700Nm of torque for the first time. The judder, apparently, was the gearbox/clutch reacting to not seeing the power it was “expecting”. The car used to go into limp mode (sticking in just 6th gear) and, eventually, threw an engine light (which pointed to the turbo).

Anyhow, this fix only lasted a few days before I started to experience the same judder.

Back to the dealer and a Mercedes Technical Case which initially found nothing. Anyhow, after two weeks, they found that the turbo actuator vacuum pipe was split (again?).

This fault was apparently quite common on the S400d. They’re pulling the car apart some more to look at the cause but this has been 20 months of looking. I’m posting here to hopefully help someone else because I can’t find anything about this elsewhere.

 

[MeanRedSpider]

Just a bit of an update as this moves towards the end of its 4th week. The dealership are now waiting on a fix from the factory. The precise failure is the turbo actuator hose getting much too hot (why?) and collapsing. The diagnostics are quite “dumb” in that they only look for a vacuum being drawn and not the actuator responding correctly. Bizarrely, the service manager thinks they may be instructed to fabricate their own solid pipe.

Part of our discussion is just how common this issue might be. The car is still pretty capable with this fault. I’ve only gone down this route because the gear shift judder on long journeys (normally towing my race car trailer). When they did the last fix, they changed the hose and, for two or three days, the car was a total beast (like it had never been in my ownership). Now I know what it should be like, I can tell when it isn’t running properly. We suspect there are other cars with this fault that the drivers just don’t know it’s happening because they’re not normally accessing the full potential of this engine and so don’t notice when the power drops. There’s no warning light and the occasional clunky gear shift on 2-hour plus journeys might not flag a problem to them.

 

[W1ghty]

Just a bit of an update as this moves towards the end of its 4th week. The dealership are now waiting on a fix from the factory. The precise failure is the turbo actuator hose getting much too hot (why?) and collapsing. The diagnostics are quite “dumb” in that they only look for a vacuum being drawn and not the actuator responding correctly. Bizarrely, the service manager thinks they may be instructed to fabricate their own solid pipe.

Part of our discussion is just how common this issue might be. The car is still pretty capable with this fault. I’ve only gone down this route because the gear shift judder on long journeys (normally towing my race car trailer). When they did the last fix, they changed the hose and, for two or three days, the car was a total beast (like it had never been in my ownership). Now I know what it should be like, I can tell when it isn’t running properly. We suspect there are other cars with this fault that the drivers just don’t know it’s happening because they’re not normally accessing the full potential of this engine and so don’t notice when the power drops. There’s no warning light and the occasional clunky gear shift on 2-hour plus journeys might not flag a problem to them.

That’s all quite worrying from a new engine . At least MB seem to be doing the right thing for you .

 

[MeanRedSpider]

That’s all quite worrying from a new engine . At least MB seem to be doing the right thing for you .

Yup - given how much work this has been, it would have been pretty horrific if it wasn’t covered by warranty. This is why I want to capture it here and hopefully give somebody else a sporting chance of resolving it in the future.

 

[alexanderfoti]

Cover pipe in heat insulation (lagging), problem solved temporarily until MB sort something else, and you get to drive the car.

 

[HappytalkAgain]

Sorry to hear about your issues. But the sentence I was most drawn to in your original post was: ‘I bought it to tow my race car around the UK’

Please tell us more, in another thread if you so wish.

 

[tonysmb]

OP, thanks for this thread which is very interesting. For me it highlights what these fora should be about, ie people sharing information to help/assist others, even if it's not of any immediate relevance to any particular individual.

As per another post of yours, a rare but very good model.

 

[MeanRedSpider]

I finally got to take a picture of the failure. Apparently, the pipe runs near the DPF - it’s clear to see how it has heated up and collapsed. I can also see how a steel or copper pipe in this section would be a useful fix

 

[MeanRedSpider]

Latest instalment: The Mercedes factory has acknowledged the issue and is developing a heat shield, apparently. They say it should take about 3 weeks to do. They had suggested to my dealer that they should replace the pipe in the meantime. We’ve agreed that there’s no point in doing that. It lasts only a few days. They were supposed to be agreeing with the dealership a different material to make the pipe from: that has been 10 days with no answer. It will soon be 3 months of the two years that I’ve owned the car that it has been at the dealership (on and off) and the car has barely worked as intended in those two years.

 

[alexanderfoti]

Cover pipe in heat insulation (lagging), problem solved temporarily until MB sort something else, and you get to drive the car.

This way you can use it!

 

[MeanRedSpider]

This way you can use it!

I assume there’s a reason why they aren’t just insulating it - eg maybe there isn’t space. I haven’t seen the location on the car

 

[alexanderfoti]

Because they will only do what mb tells them to do and nothing outside of their instructions. A bit of sane thinking by them would have given you the use of the car for 2 months but they have to cya