Sort of missfire... Any ideas?

[YorksLS18]

This is a new one on me - any ideas about what's wrong much appreciated.

Just set off in my 2011 Mercedes C-Class 250d and something is very wrong.

Engine light is on. It's idling fine. When I rev or accelerate it picks up and drops power sporadically, causing almost a kangaroo effect.

It won't go above 10mph as a result. I can't tell if it's a misfire (it idles ok) indicating an electrical or fuelling problem, but wondered if a blocked DPF would also cause this.

Any ideas before I call a tow truck...? Thanks.

[LunarOne]

Get a cheap bluetooth (android) or wifi (ios) OBD2 scanner and either Torque or OBD Fusion apps on your phone and you'll see exactly what the problem is. Much cheaper than a tow truck, and it's the only thing that's going to diagnose the issue. A dealer or garage will do the same, but with more expensive equipment that can talk to specific modules in the car, but if the engine light is on then a cheap scanner will do the trick. Or buy a dedicated scanner:
https://www.amazon.co.uk/MOTOPOWER-MP69038-Scanner...

As it's a diesel, my guess is a blocked or failed injector.

[stevieturbo]

Stuff like that hardly happens totally at random in an instant.

So what's the history leading up to this ?

[YorksLS18]

stevieturbo said:

Stuff like that hardly happens totally at random in an instant.

So what's the history leading up to this ?

The history leading up to this is it's run pretty much faultlessly for the entire seven years and 90k miles I've owned it.

A few months ago I suffered a serious back injury and couldn't drive so it stood for a few weeks, which could have something to do with it. I've been doing shorter journeys as a result which is why I thought it may be DPF related. But it has been running fine until now.

[stevieturbo]

sitting for a few weeks should not cause any problems.

Unless mice or something have been nibbling.

[YorksLS18]

Just to close off this thread, a diagnostic scan has revealed a faulty boost pipe/ sensor. It's going in on Friday for the work.

[stevemcs]

Most likely boost pipe on the NS as it joins the intercooler

[bunchofkeys]

Although not a Merc, my mother's Nissan X-Trail MY2008 has similar symptoms.
First I thought it was the fuel filter, as a lack of fuel was being supplied. This occured the other year, so initially I thought it was the same thing again.

But the code reader showed a P0045 code, related to the turbo.

A bit of dicking about with a vacume pump, to see if the turbo actuator works, turns out it was the boost sensor. Amazon were selling these for £30 a pop. Literally a two min job sorted the misfire, which appeared about 3k rpm.

[LunarOne]

YorksLS18 said:

Just to close off this thread, a diagnostic scan has revealed a faulty boost pipe/ sensor. It's going in on Friday for the work.

Thanks for getting back to us OP - always nice when someone does that and makes the thread much more useful to anyone googling the same symptoms on their car.

[YorksLS18]

LunarOne said:

YorksLS18 said:

Just to close off this thread, a diagnostic scan has revealed a faulty boost pipe/ sensor. It's going in on Friday for the work.

Thanks for getting back to us OP - always nice when someone does that and makes the thread much more useful to anyone googling the same symptoms on their car.

Thanks, and previous advice appreciated. I've never seen a misfire like that and was indeed half expecting a faulty/leaky injector or blocked DPF.

As stevemcs says above, my mechanic reckons it is the N/S intake pipe, as apparently he's had a few Merc W204s with the same issue.

So just in case anyone googles this thread with a severely misfiring and underpowered C Class, definitely worth checking those boost pipes, jubilee clips etc on lower nearside front!

Edited by YorksLS18 on Tuesday 12th September 14:58