ML 270 CDI EGR Bypass Problem?

[michael8554]

Did the EGR bypass about 6 months ago and can report that this has been successful, apart from one issue.
My ML is driven fairly gently around the local country roads, and the turbo can be heard faintly in the background.
If I give it some sustained wellie, like to pass a slow bus on a steep hill, the turbo moan becomes quite loud, which is to be expected.
However, once over the hill and cruising again with little throttle, the turbo can still be heard quite loudly, and only after 10 minutes or so of cruising do I realise it's gone quiet again.
Once things are back to "normal" I can accelerate moderately briskly away from lights without particularly noticing the turbo noise.
I've seen posts where moaning is a symptom of an air leak, but this moan isn't there all the time. About 6 months ago I also replaced the large diameter rubber hose with the male metal connector on the output of the EGR, as this connector was worn and being pushed out under boost.
While it's in its noisy mode, my passengers ask if there's a problem with the engine!
I don't remember this happening before the EGR mod, is this a normal by-product or something else?
Michael

 

[Dieselman]

Sounds like a blocked Cat.

 

[michael8554]

Thanks Dieselman, please explain how that would give my symptoms.
Michael

 

[Dieselman]

The exhaust back pressure builds under greater load, then gradually subsides again.

 

[michael8554]

Any way to clear the Cat?
Michael

 

[Dieselman]

Chop it out.

 

[michael8554]

I've been googling Cats on the ML270 CDI and blockage appears to be a common problem.
Mine isn't suffering any performance issues but it sounds like it eventually will.
It would appear that removing and de-gutting the front Cat is relatively easy, but what's the easiest solution for the second cat?
I don't want any problems at the next MOT due to suspicious sections of aftermarket pipework.
Some threads suggest leaving it alone but it sounds like the front Cat guts end up in the second Cat.
One thread suggests talking to MBS Southampton, not a million miles from me?

 

[Mickybo]

Dont think you need a cat due to the age but as long as it isn't smokey then you should be ok, the MOT doesn't test emissions on diesels, my e320cdi is doing the exact same thing and I'm gutting my precat this weekend

 

[michael8554]

So Mickybo, are you not degutting the second Cat (does E320cdi have one)?

 

[Mickybo]

Its hard to gut the other cats, mine has a precat at the turbo then the single pipe branches out into 2 pipes under the car into 2 cats beside each other then back into a single pipe to the exit

 

[Mickybo]

But I will be removing them and replacing with a piece of pipe instead, as long as it isn't smoky then it will pass the MOT.

 

[Dieselman]

Why remove the can, just empty it.

 

[Mickybo]

Don't see how I can gut the second 2, it is a fairly long piece, what would you use to empty it

 

[mejermy]

If it's like my '04 E220cdi just remove the exhaust pipe which includes the second cat (chicken wire soot trap). Delicately cut it open from above to make a 'trap door' and peel back the fold of metal to expose the chicken wire. Remove chicken wire and dispose of in an environmentally friendly manner!!. Braze closed the now empty box. Replace exhaust pipe. Nothing visible from below and the top cannot be seen.

 

[michael8554]

Since my problems started as soon as I'd done the EGR bypass, before I start the irreversible gutting of the Cats, on Thursday I'm going to remove the bypass (I did it with plugs and sockets so easy to revert) and see if I have the same symptoms on full throttle acceleration.
Of course, if it all seems good, I'll start to worry that the EGR is masking the possibly blocked Cats :-(

 

[michael8554]

Well, took out the EGR bypass, and repeated test up a local hill at full throttle (see first post in thread).
Now no funny noises!
So where has the boost gone that was possibly backing up in the exhaust?
Does the EGR bypass change the turbo action at all?
Almost got caught out by unexpected turbo lag, was stopped at a roundabout waiting to pull out across the roundabout, and got that heart in your mouth feeling when pressing the accelerator down initially did very little at all, definitely worse than after the EGR Bypass installed.