W209 P0034 turbo by pass valve control circuit low

mr spanner

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CLK 270CDI auto. Comes up with fault code P0034. Does anyone have any experience of this?

Car is really noisy when cold. Power is very poor especially in reverse when cold. Car hunts and revs fluctuate. When hot it sounds OK and runs alright until extra boost is required and then it goes into limp mode and won't go over about 2000rpm until switched off and back on again.

I have checked the vacuum hoses and switched over the vacuum transducers. Both EGR and turbo by pass valves actuate, no change in performance. I removed the turbo and checked the bypass valve was actually functional. I found no problem. Turbo looks fine. I also blew out the pre cat with compressed air. There was alot of particles flying around but it wasn't blocked. I also tried running with MAF disconnected. There was no noticeable change.

Now I am running it with the exhaust clamp loose between turbo and pre cat. This allows leakage and car doesn't go into limp mode. Side effect seems to be gear changes don't work properly. Car does not go into top gear at 80mph. Also pull off from standstill is really slow so I suspect it doesn't change down properly. Car runs great now when hot and acceleration when moving is good.

Has anyone else experienced the same? my initial thoughs are that the exhaust is restricted but this is not conclusive.
 

television

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This could well be a blocked CAT fault,,and you have almost proved that
 

Xtractorfan

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You can remove the cat and check it by lightly tapping it on the ground/floor and checking if nothing like small gold/islver flakes fall from it...or even pour cold clean water thru it and the water flows without restriction..
 

Alex Crow

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mr spanner, from what you describe this sounds like a blocked second cat - the one under the floor. try disconnecting this and reconnecting the first one. let us know how that goes.
 
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mr spanner

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P0034 turbo by pass

Thanks for the feedback. I will take a look at the CAT. Will this need replacement or can it be cleaned out? Do the gold and silver particles come from the pre cat? Presumably exhaust emissions are too high if the pre cat/cat are not in tact?

Does anyone understand why not having the exhaust properly connected to the turbo can cause gear ratio problems? I am begining to think that is a different fault? I will try sealing the exhaust again and see what happens.

This morning it lost drive altogether. I tried putting it in N and back in D but wouldnt engage. I had to switch off and back on again to get drive.

Any help is appreciated
Jon
 

television

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With the gearbox,,if the engine power is down the box does not know what to do, and it will often just lock up,, the torque converter is what it says,,and it cant torque what isnt there. these things are married closely to the engine output of the car
 
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mr spanner

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W209 P0034 turbo by pass valve

Thanks Malcolm. I removed the whole exhaust and flushed each part out with a hose. Each part seemed to allow free running water but there was a fair amount of soot. The 2nd cat seemed to be the worse. I soaked the pre cat and second cat in petrol and left it overnight expecting to see alot of black petrol come out. It was quite clean so obviously did not dislodge anything. The water seemed to have more effect. I filled the pipe up to get max flow through the cat. Allowed to dry and then put it back on the car. The clamp between 2nd cat and rear box was fractured so had to replace. (main dealer only part). Car so far is running fine. No more limp mode and 40 mpg. It seems to be a remarkable result considering I didn't find any particular issue. I guess it depends how much restriction is needed to cause a problem?

Cold running issue still exists. This causes incorrect gear ratios until warmed up and engine is switched on then off again. If you don't switch off the gear ratio selection is all over the place.

Any thoughts on the cold running/ hunting when warming up?

Thanks
Jon
 

television

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Hunting on a petrol engine can only really be an air leak on or around the manifold where more air is being taken in
 

Miffy

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Isnt raw fuel the kiss of death for a CAT ?
 

Alex Crow

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Isnt raw fuel the kiss of death for a CAT ?

only when hot and being forced fed with excess oxygen, ie when a spark plug/coil/lead fails. this is why cylinder shutdown is so efficient on cat petrol cars. this one however is a diesel.
 


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