loud tapping..

[Paul]

I changed to mobil 5w50 about 6 months ago,after the change
I noticed a tapping noise when inside the cabin at idle...
I assumed it was maybe lifters because it was in time with the engine...but last night I had a hunt around and discovered there was a pipe coming from my throttle body,through a non-return valve,down to a solinoid and down under the chassie back to my fuel tank.
I guess the system pulls fuel gases out of the tank under idle or decaleration via the vaccum of the throttle body.
the tapping noise was the solinoid flicking on and of rapidly.
So i ring MB and they tell me that replacing the solinoid probley wont make a difference....:rolleyes:

I have a 230k and the solinoid is located just in front of the window wiper water tank.
Has anyone had this before??
or is my engine running so quite that i now hear that!!
any help would be all good:) :)

[36AMG43]

I have a tapping noise at idle and the dealer said that it could be the Camshaft Adjuster Assembly. Others say that it is normal and they have used Lucas oil Stabilizer and it worked. i have also been using 94 Octane Gas and it has reduced the noise.

[SLAMMED_C]

I changed to mobil 5w50 about 6 months ago,after the change
I noticed a tapping noise when inside the cabin at idle...
I assumed it was maybe lifters because it was in time with the engine...but last night I had a hunt around and discovered there was a pipe coming from my throttle body,through a non-return valve,down to a solinoid and down under the chassie back to my fuel tank.
I guess the system pulls fuel gases out of the tank under idle or decaleration via the vaccum of the throttle body.
the tapping noise was the solinoid flicking on and of rapidly.
So i ring MB and they tell me that replacing the solinoid probley wont make a difference....

that would be the MOT valve.. its part of your evaporative purge system. they do make some noise when in operation, some are noisey, some are quiet.. check the rubber bracket it attaches to, maybe its broken and now touching something and the pulses are magnified in the cabin. check the lines to see if they are touching anyhting also.. you can try and insulate things so they dont touch.

[1998K]

Originally posted by SLAMMED_C
that would be the MOT valve.. its part of your evaporative purge system. they do make some noise when in operation, some are noisey, some are quiet.. check the rubber bracket it attaches to, maybe its broken and now touching something and the pulses are magnified in the cabin. check the lines to see if they are touching anyhting also.. you can try and insulate things so they dont touch.

This is intersting, please which is the acronym of MOT? How does the evaporative purge system operate?

Does it require some kind of maintenance: cleaning or something similar as routine?

Thanks

Hi:)

[SLAMMED_C]

well, mercedes lists the acronym MOT (in their glossary or terms) meaning MOTor.
but the MOT valve is also known as a purge valve.. it pulses and directs fuel fumes back into the intake manifold.

http://memimage.cardomain.net/member_img_b/266992_121_full.jpg

I hope this picture I drew helps put a bit.. basically when you fill up your gas tank.. the excess fumes go into the activated charcoal cannister, the shut off valve vents to atmosphere, the mot valve pulses to let fumes come out of the charcoal cannister and into the intake manifold to be used in the engine (gets added to the incoming air)
whan you have code po455, it means a major leak in the purge system, either the gas cap is not tightened properly or is off completely, causing no pressure build up inside the tank or the shut off valve is faulty and not shutting (staying open venting to atmosphere). there is also a code po450 I think, for minor leak in purge system, this can be also the shut off valve, maybe sticking slightly causing only a minor leak, or it can be a mot valve not closing, or a leak in one of the lines somewhere.
hope this helps a little bit.
no maintanance is required.. you can try replacing the MOT valve if you wish.. but its not cheap.. just maybe try and insulate it to stop the vibrations going through the car.
I know on the W203 chassis there was a recall for the cars with excessivly noisey MOT valves.. you could feel it inside the car, so we just insulated the underneath or the valve.

[1998K]

Originally posted by SLAMMED_C
well, mercedes lists the acronym MOT (in their glossary or terms) meaning MOTor.
but the MOT valve is also known as a purge valve.. it pulses and directs fuel fumes back into the intake manifold.

http://memimage.cardomain.net/member_img_b/266992_121_full.jpg

I hope this picture I drew helps put a bit.. basically when you fill up your gas tank.. the excess fumes go into the activated charcoal cannister, the shut off valve vents to atmosphere, the mot valve pulses to let fumes come out of the charcoal cannister and into the intake manifold to be used in the engine (gets added to the incoming air)
whan you have code po455, it means a major leak in the purge system, either the gas cap is not tightened properly or is off completely, causing no pressure build up inside the tank or the shut off valve is faulty and not shutting (staying open venting to atmosphere). there is also a code po450 I think, for minor leak in purge system, this can be also the shut off valve, maybe sticking slightly causing only a minor leak, or it can be a mot valve not closing, or a leak in one of the lines somewhere.
hope this helps a little bit.
no maintanance is required.. you can try replacing the MOT valve if you wish.. but its not cheap.. just maybe try and insulate it to stop the vibrations going through the car.
I know on the W203 chassis there was a recall for the cars with excessivly noisey MOT valves.. you could feel it inside the car, so we just insulated the underneath or the valve.

SLAMMED_C you are really a qualified friend thank you.
I belive yesterday I have individuated the MOT valve: it's a small black cilinder on left side of engine (mine is a kompressor) really does it cost a lot? Fortunately mine is not noisy.

Does the shut off valve in the rear open only in case of excessive pressure in the system/fuel tank? Othervise the flux is only from the tank to the manifold?

My question came out after seeing something in the Haynes Manual, they refer to some maintenence job (B service if I'm not wrong) to the device arranged in the rear wheel arch. Boh


But does this kind of system together with EGR and oil vapour recycle from the engine, affect engine performances itself?

Thanks a lot

Marco