pulsing sound from cylindrical unit in engine bay

[recycled]

Hi all
Does anyone have a pulsing throbbing sound that starts and stops now and again from a white cylindrical object near the ABS unit of my w202 sport c180 1997spec it starts about 5 mins after i start up and then goes away then restarts, i took it to MB north west and they said every model makes the sound there .Also there is a black box under my passenger seat with a red plug sticking out of it that goes underneath the floor carpets towards the front. does anyone know what it does?. The seats are not heated either
Thanks

 

[Bazzle]

Pic would be nice.

Without seeing it.

Could be heater valve (they pulse dependant on temp setting.)
Fuel tank purge valve
Both normal

Bazzle

 

[recycled]

Thanks i was coming to that . the third pic is what is under the front seat. looks like the back of a wireless router to me. LOL

 

[Stratman]

No idea about the white cylinder thingy (A wider angle picture might help a bit more) but the gubbins under the seat could well be the pressure switch which detects the presence or absence of a passenger. This information is used for the seat belt warning light and to avoid firing the passenger side airbag(s) when the seat is unoccupied.

 

[GRAV888]

Does it have 'MOT' written on it?
Mine clicks all the time.

 

[GRAV888]

BTW, the bracket is rusty, not the car

 

[recycled]

No it has not got M.O.T on it. who put that there? is it your garage?Well it just does my head in when it is idling completely silently then you hear a throbbing sound . i have checked in some elegance specs and they have not got it. has it got to do with some suspension?

 

[GRAV888]

No it has not got M.O.T on it. who put that there? is it your garage?

No.
It has always been there.
There is one on my CLK too that clicks all the time as well, but that doesn't have MOT stamped on it.

As for the plug under the seat, it could be a seat sensor for the air bags.

 

[Stratman]

Have you traced the pipes from it to see where they go?

 

[recycled]

Thanks all especially grav888. no i havent traced the wires ,could not be bothered. it is because the missus has been robbing my car of late but as long as the thing works properly i am completely made up with it.
How do the w203 cars fare. i heard bout build quality issues form south africa. Do they still make them there or have they moved back to germany

 

[nigel cross]

I think its called a purge regeneration valve, and its to do with???
Something regarding emissions

 

[Stratman]

My Haynes W202 manual says that the purge valve is "Clipped to the bulkhead, at the rear of the engine bay".

 

[recycled]

i shall smash thecar headlong into a wall with a passenger in the seat to check if the pressure thingy under the seat still works.

 

[Dieselman]

i shall smash thecar headlong into a wall with a passenger in the seat to check if the pressure thingy under the seat still works.

Can you post some pics and a proper write-up.

 

[Dieselman]

I think its called a purge regeneration valve, and its to do with???
Something regarding emissions

I'd go with this idea. It looks like the purge control valve which releases nasty benzine into the engine from the charcoal cannister, only under high vacuum conditions (idle) when warm.

 

[LastMinute]

Cooling water preheater? (See Detali page.) Don't know why it would pulse, though.

(Before anybody says it - yes, I know the pictures aren't a W202, but the selected vehicle is.)

Edit: seems unlikely, given the footnote. When was the last time you plugged your car into the mains?

 

[Stratman]

I'd go with this idea. It looks like the purge control valve which releases nasty benzine into the engine from the charcoal cannister, only under high vacuum conditions (idle) when warm.

The exact opposite, according to Haynes. Extract from C-Class manual:-

"The flow of fuel vapour from the charcoal canister through the purge valve to the throttle body is controlled by a thermo-valve, which prevents the purge valve opening until the coolant temperature exceeds a preset limit.This is to ensure that the engine runs correctly when it is cold and to protect the catalytic convertor from the effects of an over-rich mixture. In addition, because the purge valve is controlled by engine vacuum, the charcoal canister is only purged when the engine is under load. This prevents an over-rich mixture from bring supplied at idle, preserving idle speed stability and low-speed driveability"

 

[recycled]

Cooling water preheater? (See Detali page.) Don't know why it would pulse, though.

(Before anybody says it - yes, I know the pictures aren't a W202, but the selected vehicle is.)

Edit: seems unlikely, given the footnote. When was the last time you plugged your car into the mains?

Looks like that is for an electric merc in a turkish laboratory LOL
Why would you need to preheat cooling water in the car?

 

[Dieselman]

Looks like that is for an electric merc in a turkish laboratory LOL
Why would you need to preheat cooling water in the car?

If you live somewhere cold, it warms the heater and the engine before a cold start.
If the temperature gets too cold even the oil will gell.

 

[recycled]

yes i know that but the injectors took care of the choke system to enable cold starts.Do you have to plug that into the mains as well?