OM646 diesel leak-off pipe T-piece

[selphy]

Afternoon all,
My 2008 E220CDi seems to have air in the low pressure diesel pipework near the fuel filter. When I turn the ignition on you can hear a lot of air bubbles rushing through the pipework for about 20 seconds, presumably as the lift pump in the tank operates. I suspect that air is being drawn into the T-piece that joins the injector leak off pipework to the fuel filter pipework as that's where the noise is loudest. If I "stethoscope" it with a length of plastic tube it does sound like air is leaking into that joint.

The car starts and runs OK but if there is a problem here I'd rather sort it now rather than break down somewhere inconvenient.

Can anyone confirm that there should be no air in this pipework and if the T-piece is known for letting in air? It seems to be assembled from two parts clipped together so it may have some o-rings that I could replace.

Thanks

 

[W209CLK270]

There should be NO air in the fuel supply system. As you already suggest there is an issue with either a cracked plastic union ('t' piece) or/and a seal or two. Has the fuel filter been changed recently as this could be at fault i.e. not correctly seated/sealed. Good luck!

 

[selphy]

Thanks.
Yes, I had a new fuel filter fitted a couple of months ago with annual service done by independent garage. The fittings seem tight but maybe I should replace the hose clamps and see if that helps.

 

[selphy]

Well, I've checked and double checked all the fittings and hoses and I'm sure there are no leaks. The o-rings on the injector leak off pipes look perfect too.

I took apart the T piece (as it is formed by two sections clipped together) and I now believe that it is actually a venturi device to help suck fuel from the injector leak off ports. I now think that there is actually nothing wrong and the sound isn't air at all, just the noise of fuel passing through the venturi.

Could someone in the know confirm this? Or even better, could someone else with a similar OM646 engine perhaps have a listen for what sounds like rushing fuel / air coming from the T piece when the ignition is turned on? It is probably completely normal and I just hadn't noticed it before.

Thank you

 

[Mintyfresh77]

Well, I've checked and double checked all the fittings and hoses and I'm sure there are no leaks. The o-rings on the injector leak off pipes look perfect too.

I took apart the T piece (as it is formed by two sections clipped together) and I now believe that it is actually a venturi device to help suck fuel from the injector leak off ports. I now think that there is actually nothing wrong and the sound isn't air at all, just the noise of fuel passing through the venturi.

Could someone in the know confirm this? Or even better, could someone else with a similar OM646 engine perhaps have a listen for what sounds like rushing fuel / air coming from the T piece when the ignition is turned on? It is probably completely normal and I just hadn't noticed it before.

Thank you

Hi Selphy,

Did you find out if all was well with this? I posted a video yesterday about exactly the same thing.

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Cheers Chris

 

[mersum1es]

No venturi effect designed, just linked leak hoses... of course if previous injector leaks a lot, it will get some venturi effect...

 

[Mintyfresh77]

No venturi effect designed, just linked leak hoses... of course if previous injector leaks a lot, it will get some venturi effect...

Selphy was correct. Venturi is part of Delphi system on OM646 Evo and it's what I've been hearing. Fuel from filter is forced through T section plastic pipe en route to HPFP. The T section also receives leak back from injectors which is returned directly to HPFP thus Venturi effect created.

 

[Mintyfresh77]

No venturi effect designed, just linked leak hoses... of course if previous injector leaks a lot, it will get some venturi effect...

 

[mersum1es]

Ahh.. ok I was thinking injector t coupling... but true, that junction coupling creates venturi effect tp whole return line.. Thought picture shows it goes back to the tank, not to high pressure pump, whih is actually good in cooling point of view.