Hissing noise from central locking ( 230 CE ) ! ???

[petef]

Since i have had this car ( 1991 230ce) there has been a loud hissing noise every time i lock the door or open it !...It lasts for about 10 secs then disapears. It seems to be coming from the petrol tank area. It sounds like a tyre being let down and the air escaping. I think i read that the central locking is controlled by air !!! Is this right ? ...and secondly should it make this noise ?

Advice welcome !!

 

[Ian B Walker]

The central locking also locks the fuel flap. Check that the vac hose that goes to it hasnt split or come off.

 

[petef]

Thanks Ian, will try tomorrow morning....where do you get all this merc knowledge from ???? !!!!! Will let you know how i get on.

 

[andy_k]

Ian's diagnosis could well be spot on but I'd be surprised if the central locking pump ran for ten seconds, the locks work on a fairly low pressure vacuum system so a hissing is possible but I'd be amazed if you could hear it outside the car as all the connections are inside - if only it were that easy to troubleshoot these systems (trust me it's not).

Do the other lock buttons go down quickly and is the fuel filler cap locking quickly?

However,

1, does the noise happen if you get out of the car and not lock it?
2, does the noise happen if you lock the car with the engine running?

It's possible the noise you are hearing is related to the fuel system, maybe the fuel pumps as they are under the car at the rear where you would expect to find the fuel tank (yours is behind the rear seat) or it could be one of the fuel tank breathers.

Do you have the correct fuel cap fitted?
Does the noise seem better or worse if the fuel level is higher?

I'm not discounting Ian's advice as he could well be right but I'm just offering an alternative

HTH

Andy

 

[Ian B Walker]

Listen to Andy. He has mentioned things here that I hadnt thought of. His diagnosis is probably more accurate than mine. As for knowledge, hang around here for a while and you too will be offering advice before long

<edit>.....quietly supprised that this thread has stayed here as long as it has, Mods must be asleep