Ok here goes!

[barrieeld]

Been having a bit of a fault finding exercise recently with my s320cdi.

It seems at random points it completely looses power, like it will rev up past 3000rpm but there's no guts at all. I turn the engine off then on again the the car runs like a dream with full power.

Now im thinking EGR but i was under the impression that this happened after around 5 mins...ive driven for up to 2 hours and this doesn't happen and other times it happens after 5 mins?

Ive already replaced the MAF and it hasn't made any difference, ive also redone all the pipes going into the turbo too. Its really annoying me now and without having to go through the "never ending fault finding costs"

 

[DieselE]

It's quite possible that it is going into "Limp Home" mode. This would explain the resetting when you shut down.

Despite your not wanting to do it, I'd suggest getting the fault codes checked.

 

[barrieeld]

Hi there thanks for the response.

Ive had it on both indy and my local stealership and there are no faults when on diagnostics?

 

[television]

2 things come to mind, is there any oil going onto the MAF, by unplugging it, if the car runs reasonably OK then the new MAF is at fault The MAF at fault would not show up on the STAR

 

[barrieeld]

Hi again Malcolm.

The new MAF was tested and ran out by the mechanics but still went into "limp" so they decided it wasn't that, im not too sure what else could be the problem here....its like when the car is floored it tends to kick in more than ofter, not every time though, maybe some issue with air flow to and from turbo?

 

[grober]

What about a gearbox ECU problem causing the main engine ECU to go into limp home mode? Whats the age+ mileage on the car?

 

[television]

What about a gearbox ECU problem causing the main engine ECU to go into limp home mode? Whats the age+ mileage on the car?

I dont think so, if it did it would fire evenly even if the speed was reduced to limp home

 

[MecrazyBenz]

Must be catchy Not hijacking the thread but....

Iv had the exact same symptoms on my 98 w202 c200 manual 160k. It seems to be getting worse too. Idles rough sometimes. But when the car is switched off then on again, fault gone.

I have started switching off/on mid driving now just so I can accelarate to keep up with traffic. I have showed it to 3 machanics and they suggest different things...possibly spark plugs/blocked injectors ???

Had the MAF unplugged and revved but same issue.

Fuel consumption increased also. Have you noticed this on yours ?

Just want rid of this car now

Sorry back to your car....

 

[Glenn Smith]

Been having a bit of a fault finding exercise recently with my s320cdi.

It seems at random points it completely looses power, like it will rev up past 3000rpm but there's no guts at all. I turn the engine off then on again the the car runs like a dream with full power.

Now im thinking EGR but i was under the impression that this happened after around 5 mins...ive driven for up to 2 hours and this doesn't happen and other times it happens after 5 mins?

Ive already replaced the MAF and it hasn't made any difference, ive also redone all the pipes going into the turbo too. Its really annoying me now and without having to go through the "never ending fault finding costs"

A MB dealer should be able to quickly identify the problem, this sounds like either an EGR or boost pressure control fault/ turbo fault

 

[barrieeld]

boost pressure control fault what are the exact symptoms?

I don't think its the turbo because A) it had a new one just 3 months ago and B) it wouldn't have any grunt full stop I assume?

Thanks for the help so far folks, hope to get this sorted ASAP.

 

[DieselE]

I've linked the post below because Dieselman (a forum member who is very knowledgeable about engines) is currently absent.

http://www.mbclub.co.uk/forums/showpost.php?p=252764&postcount=18

Having made the link, I remembered you saying that there is no fault showing when the car is coupled to STAR, so maybe a wastegate fault is not the answer.

 

[barrieeld]

hmm sounds interesting...would this realy be the case with only having a new turbo installed literally in september?

but when it does go into "limp" so to speak it does feel like when you put the window down you can hear the turbo hiss like its spinning but the boos isnt being applied.

 

[John Kerr]

I've linked the post below because Dieselman (a forum member who is very knowledgeable about engines) is currently absent.

http://www.mbclub.co.uk/forums/showpost.php?p=252764&postcount=18

Having made the link, I remembered you saying that there is no fault showing when the car is coupled to STAR, so maybe a wastegate fault is not the answer.

There is no waste gate on a CDI they have a variable vane turbo.There is an acctuater on the side of the turbo worked by vaccum a good place to check is the rubber pipe from the transducer down to the turbo

 

[barrieeld]

what should i be looking for exactly and what would be the symptoms? somthing similar to what i am getting now?

 

[BlackC55]

I would be looking at the transducer(s) as the possible fault.

The boost pressure sensor is also a possibility. It is unlikely to be the EGR but not completely impossible.

 

[barrieeld]

thanks for the reply.

Will any of these issues fail to show on the diagnostics machine.

 

[BlackC55]

Nope.

Vacuum transducer will only show a code when it is unplugged. (electrical)
It won't give a "specific" code but may give "Low boost pressure" type code.

I have not tested one with a vacuum guage before......... I will try that when I get one next with a similar problem

 

[barrieeld]

I think the prob the garage were having is that its happening intermittently, so one you turn off the power hook it up to the machine all is good again, seems pretty hard to actually find our what the prob is.