Poor performance, no turbo - ECU ?

[paulfoel]

I've posted about this before re my C250TD 1999.

Basically, now and then I get really poor performance, like no turbo etc. Seems to last for a few trips and then its OK again for a few weeks.

Sound like an ECU problem? Do other garages (apart from dealers) usually hae to diagnostic tools to look at this?

Whats the worse possible outcome? New ECU needed (gulp!) ? How much?

I'm sure I saw somewhere that there was a way to reset the gearbox or something? How do u do this?

Is there any way to do a super duper reset of the ECU?

 

[spitzkop]

I've posted about this before re my C250TD 1999.

Basically, now and then I get really poor performance, like no turbo etc. Seems to last for a few trips and then its OK again for a few weeks.

Sound like an ECU problem? Do other garages (apart from dealers) usually hae to diagnostic tools to look at this?

Whats the worse possible outcome? New ECU needed (gulp!) ? How much?

I'm sure I saw somewhere that there was a way to reset the gearbox or something? How do u do this?

Is there any way to do a super duper reset of the ECU?

ECU would be the last item to look at.
When the ECU detects a fault (a sensor returning impossible values in respect to itself or other sensor values), it switches itself into Limp Home mode, ie. converts the engine into a basic non-turbo normally aspirated diesel engine which is rev limited and speed limited (a knock on from rev limited).
Initially, the first culprit to look at is the Mass Air Flow sensor (or MAF). This little unit detects how much air per unit volume is flowing into the engine and what its temperature is. This unit gets old or caked up with crap and can register as a logged fault or a non-logged fault within the ECU, both switching it into Limp Home mode. Look at Parrot of Dooms excellent HowTo on the subject, he shows how to clean it.
If after youve given it a clean, you still have the problem, then you need to buy a new one (preferably on a return basis) as sometimes cleaning it will not be sufficient. If a new one doesnt rectify the situation, post some more info and we'll see what further analysis can be made.

 

[paulfoel]

ECU would be the last item to look at.
When the ECU detects a fault (a sensor returning impossible values in respect to itself or other sensor values), it switches itself into Limp Home mode, ie. converts the engine into a basic non-turbo normally aspirated diesel engine which is rev limited and speed limited (a knock on from rev limited).
Initially, the first culprit to look at is the Mass Air Flow sensor (or MAF). This little unit detects how much air per unit volume is flowing into the engine and what its temperature is. This unit gets old or caked up with crap and can register as a logged fault or a non-logged fault within the ECU, both switching it into Limp Home mode. Look at Parrot of Dooms excellent HowTo on the subject, he shows how to clean it.
If after youve given it a clean, you still have the problem, then you need to buy a new one (preferably on a return basis) as sometimes cleaning it will not be sufficient. If a new one doesnt rectify the situation, post some more info and we'll see what further analysis can be made.

Yes. I've found Parrots post. I'll have a look at that.

Any idea how much a new MAF is?

 

[Harley Man]

the only problem with this is the C250TD does not have a MAF it could be the MAP is getting near the limit or something wrong with the EGR valve, mine stuck open once and the fault was as you discribe, anyone with an universal analiser that will read the merc codes can help you see if there is a clue in the ecu. Where do you live?

Harley Man

 

[spitzkop]

Thanks Harley Man, but 1999 still using a MAP! MAP has a similar purpose to MAF, ie. determine airflow into the engine. Sorry, Paul, I dont have direct knowledge on MAP so cannot help further!

 

[Harley Man]

Yes but the difference is the MAF or MAS measures airflow volume and is not used on the C250TD of any year, the MAP measures pressure so the ecu knows what boost the turbo is providing. The other sensor the C250 has, which looks like a MAF is purely an air temp sensor.

Harley Man

 

[spitzkop]

On the 220/270/320 it has a MAF before the Turbo and a Boost Pressure and Boost Temperature after the intercooler. I wrongly assumed that a 250 of similar year would have the same setup.

 

[Harley Man]

Thats the difference between the traditional low pressure diesel and the CDi's, I have had both and much prefer the old low pressure setup, its simpler and easier to repair, the downside is the economy is not quite as good, the upside in my experience is improved reliabilty and lower repair costs. But my CDi I had was a 2001 W203 and the build for that year seemed to be particualy bad, every part I replaced (lots of parts!) was updated or modified.

Harley Man

 

[paulfoel]

the only problem with this is the C250TD does not have a MAF it could be the MAP is getting near the limit or something wrong with the EGR valve, mine stuck open once and the fault was as you discribe, anyone with an universal analiser that will read the merc codes can help you see if there is a clue in the ecu. Where do you live?

Harley Man

Ah. No good looking for the MAF then?

Is there anything similar I can do with the MAP?

Live - Newport, South Wales.

 

[paulfoel]

Thats the difference between the traditional low pressure diesel and the CDi's, I have had both and much prefer the old low pressure setup, its simpler and easier to repair, the downside is the economy is not quite as good, the upside in my experience is improved reliabilty and lower repair costs. But my CDi I had was a 2001 W203 and the build for that year seemed to be particualy bad, every part I replaced (lots of parts!) was updated or modified.

Harley Man

Yeh. Economy is not great on my C250 (for a diesel anyway). About 31mpg.

 

[KLP 92]

I beleive there is a turbo actuautor located on the air filter housing that can also cause the turbo to not work. Check al the vacuum pipes on this first.

Other causes for power loss are MAP sensor (as discussed earlier), faulty EGR valve, leaking turbo pipes.

 

[paulfoel]

Stangely enough I did old 'reset' thing and its a LOT better...

Still not quite right above 65/70mph but about 70% better. Weird or what?

 

[GSMGuy]

Stangely enough I did old 'reset' thing and its a LOT better...

Still not quite right above 65/70mph but about 70% better. Weird or what?

What reset was that then??

Mike

 

[BlackC55]

This sounds like the vacuum transducer causing a problem. It is a black coloured vacuum valve with small vacuum pipes coming off it.

Try it they are only cheap

 

[mstar01]

i too have some iffy performance in my c250 especially when i am going up hill and i see fiesta's whizzing past me i really have to give it some welly to get up the hill.

Is there a easy check to see if i might have a part on the way out?

 

[paulfoel]

This sounds like the vacuum transducer causing a problem. It is a black coloured vacuum valve with small vacuum pipes coming off it.

Try it they are only cheap

hmm. Been trying to sell this car but intermittently its displaying this problem....

to recap:-

1. Happens occasionally (one day its OK next day not)
2. When you accelerate/kick down revs rise but speed doesnt.
3. Mercedes dealer has alrady had a look and suggested Diesel injector cleaner !!!

How much is a vacuum transducer ??? How hard is it to fit? Anybody got a pic?

 

[Parrot of Doom]

The vacuum transducer is well worth a punt.

You can just about see it in this picture:

http://www.flickr.com/photo_zoom.gne?id=146226403&size=o

It's the black plastic cylinder on the lower left of the image, with 2 plastic pipes heading into the top of it, one of them via a black rubber boot.

It won't be there on yours. Its probably just underneath the turbo. I'm posting that picture to show you what it looks like. Mine has two, the turbo one is just about visible here:

http://www.flickr.com/photo_zoom.gne?id=149326535&size=o

You can see the grey vacuum pipe heading to it, at the bottom of the picture. The transducer is underneath the air intake pipe in that picture.

It has 3 vacuum pipes (2 on the top, 1 on the bottom), and an electrical connector.

Make sure you know which pipes go where, and disconnect it. The pipes all pull off, the electrical connector just needs your fingernails to release the clips.

Try cleaning the electrical connection, and checking those vacuum pipes for blockages. You never know.

 

[BlackC55]

before you go replacing it it is worthwile checking the vacuum lines to and from it for leakage

 

[paulfoel]

before you go replacing it it is worthwile checking the vacuum lines to and from it for leakage

Best way to check for leakage?

 

[paulfoel]

Sorry its duplicated from my other post....