Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

I have posted this problem on a Merc forum but I get the impression that not many Mercedes owners do their own repairs, so I am hoping someone on here might be able to help.

When first started the car will reach full revs and will go like a train, after a few minutes the turbo boost drops off to virtually nothing above 2000 rpm, if you stop and restart its OK again for a while.

Most of the advice I get from the other forums is have the codes read but the cost of that is disproportionate with what I paid for the car.

I have changed the thermostat and temp sensor as it was faulty anyway but no difference. this fault seems to be fairly well documented so I would have thought someone would have known what the problem was even if it was repaired by a garage. Leaky hose and vacuum systems don't seem to be the problem as it will go like a rocket when first driven.

I have been driving it like this since last year when I bought it and 95% of the time its fine at 2000 rpm max as it had bags of torque and a 6 speed manual gearbox and will do 70 mph up most hills, its only when I go up a particularly steep one it causes a problem, changing down doesn't help as you run out of revs. I like the car and it will do 60 mpg+ on the motorway so could live with it as it is, but the full power would be nice occasionally.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - dieselnut

It's probably the turbo variable vanes sticking, but you will need a diagnostic code read to be sure.

You don't have to go to a Mercedes dealer, just Google car diagnostic services in your local area.

Alternatively, join one of the Mercedes owners forums, there are usually local members with the software & laptop who will help to diagnose problems for a few beer tokens.

Once you have the fault codes you will have more idea of the exact problem.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

Thanks. When you say the vanes sticking, could that cause overboost which is shutting it down? I do have a code reader which will show boost pressure but when used it showed no boost pressure over 2000 rpm but when you first drive it the boost feels tremendous, I will have to try it when its in 'full power' mode. Do you know what the max pressure should be?

Mercedes C220 Cdi W203 - Revs limited to around 2000. - dieselnut

The turbo vanes are in the full boost position for most of the time, so that is where they stick with carbon clogging up the mechanism.

The ECU then has to cut fueling to stop overboost.

I would think maximum boost would be around 1.4 Bar.

If it is the turbo vanes, taking it apart & cleaning out the vane operating mechanism is usually successfull.

Look for a " how to " on youtube.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - elekie&a/c doctor
You need to find diagnostic equipment that will show data in much greater detail, especially desired and actual boost pressure.
Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

Thanks for that but with my budget I think I will have a go at the turbo first.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - Mike H

Why waste your time? How can it be easier to remove and clean a turbo rather than get the codes read by a local garage? Even if they can't fix it, at least the codes will tell you what the problem is (probably). Alternatively, you could buy a generic code reader from Ebay for £25 and read them yourself. Once you have the codes, you can google the cause/fix for the code.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - elekie&a/c doctor
Sadly you can’t fix cars using only fault codes. These codes are often the result of a problem, not the cause.
Mercedes C220 Cdi W203 - Revs limited to around 2000. - SteveLee

Could also be a faulty boost sensor, if these go out of range or fail it'll go into limp-home mode.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

I have a code reader but they are very limited as to what they will read on early 2000s cars. Mine tells me that the boost is dropping off at 2000 rpm but I could already feel that and have subsequently proved that to be the case.

I have been running Citreon,Peugeot engines for the last 10 years and although I have the proper Lexia code reader I can rarely get it to work properly but have always managed to fix any problems without it. Having a complete car for spares helps.

Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

Steve. Do you know where the boost pressure sensor is located?

Peter

Mercedes C220 Cdi W203 - Revs limited to around 2000. - Peter.N.

Well it doesn't appear to be stuck vanes as the lever moves quite easily from one end to the other, both manually and when you rev the engine.