ML 270 engine surge at 70 mph - rev counter flicks between 2500 -2300 rpm

[270 newbie]

Hi,

Can anyone assist with the problem i'm experiencing with my new car? This is the 1st Merc i've ever owned and has took the shine off it.

When you are driving on a Motorway, as the speed hits 70 mph at 2500 rpm, you notice what can only be described as a surging in the engine, as though you are taking your foot on and off the gas. It feels as though the car is being bufferred by a very strong headwind and is trying to fight it. When this happens, when you look at the rev counter needle, it flicks between 2500rpm to 2300 rpm. If you then boot it to the floor, the car picks up, goes past 70 mph and the problem disappears. Annoyingly, it only happens at 70mph.
I've read a few threads, including one very similar to the problem I am encountering, but as yet, have not found a definitive answer to the issue.

Can anyone advise me what is causing the issue?

Many thanks in advance.

 

[kwakdonut]

2500 rpm? Are you sure it's in top gear?

 

[thedman]

Is the autobox jumping up and down the gears?

 

[270 newbie]

Thnaks for the response Kwakdonut? Waht is it that makes you think it wouldn't be in top gear? Would the revs be lower than 2500rpm?

 

[270 newbie]

Hi thedman,I don't believe the box is jumping. The gears are smooth up and down the box and the kick down works fine. The only time that this issue manifests itself is at 70mph and feels as though you are experiencing driving into a very very strong headwind that keeps nudging you back with the engine fighting the headwind.
There has to be a logical explanation as to why you can see the rev counter pulsating between 2500 - 2300 rpm when this issue starts.

Any clues as to what it might be? I've already changed the 1st Cat from the back of the turbo and this has made no difference whatsoever.

Thanks

Dave

 

[Brian WH]

I also would suspect the gearbox, when was the gearbox oil last changed?

 

[x332race]

I had a similar problem recently with my C270......surging around 2000rpm mark. I also had clouds of black smoke out behind.

Eventually traced it to a split in the air hose between the inter-cooler and the manifold. Cost £55 for new hose (hose is on the passenger side of the engine and is fairly obvious once you take the engine covers off)

Suspect you may have a similar problem with fuel / air delivery?

Check to see if you have large amounts of black smoke behind, especially when accelerating.

Car is now back to normal...no surging and no black smoke.

Get it on a Star diagnostic machine to tell you what is wrong.

 

[ODUTEC]

intercooler hose

Hi thedman,I don't believe the box is jumping. The gears are smooth up and down the box and the kick down works fine. The only time that this issue manifests itself is at 70mph and feels as though you are experiencing driving into a very very strong headwind that keeps nudging you back with the engine fighting the headwind.
There has to be a logical explanation as to why you can see the rev counter pulsating between 2500 - 2300 rpm when this issue starts.

Any clues as to what it might be? I've already changed the 1st Cat from the back of the turbo and this has made no difference whatsoever.

Thanks

Dave

Dear Dave
The intercooler hose you mentiontioned ...how big is it and what component is it connected to...

Thanks

 

[simon.dachtler]

Hi 270Newbie

I have recently purchased a C220 CDi and I'm experiencing the same type of "surging" mine runs like it between 1500-2500rpm. Did you resolve the situation ?

I've recently had a turbo hose replaced which had been causing the car to continually drop into limp mode but this might be a different pipe that needs replacing ?

cheers

Simon

 

[gtvlusso]

Hi,
Not a common problem - but more than likely to be a split pipe or a loose pipe.

Check left side of engine (as you look at it):

From Turbo to EGR and Airbox pipes.

You will need to remove engine covers for a proper look around.

Suggest it is not expensive to be fixed by a specialist.

Also - Change your gearbox oil and filter every 40k.

 

[st4]

Are you sure the rise and drop and revs isn't to do with your feet being lifted from the pedal. The torque convertor never fully locks up on the 5speed 722.6 box. What therefore happens is say you at at 70mph 2500rpm with your foot on the go pedal, you lift, the revs will drop by 200rpm and the speed stay the same mominterally. Saw this all the time on my E220cdi. 60mph was 2000rpm with feet on accelerator, 1800 when off as the TC is slipping all the time, marginally when the car is being driven in 5th