Xantia - Hiss sound long after parking the car

[lancia58]

Hi

Sometimes after long after I parked the Xantia ( even overnight ) I can here a sound like a valve is open , then a hiss sound, then a sound like a valve is closed. The duration between the open and close is less than a second I would say half a second. Anyone knows the source of this ? Is this normal ?

The car is also fitted with an air conditioning , I do not know if this is related.

Thanks
Zohar

[xantia_v6]

I believe that it is the fuel pump running briefly. The hiss is the fuel going through the pressure regulator and the click is the fuel pump relay. It is normal (for a petrol engine), maybe it is to avoid vapour lock due to hot petrol in the fuel rail?

[lancia58]

Hi
Thanks, I just forgot to add that it occurs even I do not turn on the car. Is what you wrote in your answer can occur even when the car is not turned on ?

Zohar

[Mandrake]

Many petrol engines will run the fuel pump briefly a few times after the engine has been turned off. Typically it might run for about a second each time, maybe once every 5 minutes for a maximum of about 30 minutes.

This is to minimise the chances of the fuel in the fuel rail boiling due to heat soak from the engine which would otherwise cause vapour lock and difficulty starting a hot engine. Since the boiling temperature of the fuel drops when pressure drops if the pressure drops quicker than the fuel rail cools the fuel will boil. Running the pump periodically keeps the fuel rail pressure topped up until the fuel rail cools sufficiently.

This brief operation of the fuel pump will happen when the ignition is turned off even if the car is locked and empty, however as far as I know it wouldn't still be doing this the following day. (On my Xantia V6 I'm pretty sure it stops after about half an hour)

So I'm not sure what your noise is, but I don't think it's this if it's still happening 8 hours later...

[wurlycorner]

This isn't the suspension electro valves is it?

[CitroJim]

I never knew that about the fuel pump running long after switchoff...

[Mandrake]

I never knew that about the fuel pump running long after switchoff...

Surprised you haven't noticed it before Jim.

It's a brief activation so you have to be nearby and paying attention to notice it. It's why I never disconnect the fuel lines without removing the fuel pump fuse or disconnecting the battery!

[CitroJim]

I never knew that about the fuel pump running long after switchoff...

Surprised you haven't noticed it before Jim.

No, honestly, never heard it (or not consciously).. I will be listening out for it now..

It's like I didn't appreciate what lane ropes did in a swimming pool to isolate the the lanes until it was pointed out to me...

[lancia58]

It happens even if the car parked for two days. What is the electro valves? What is its function and how can it be related ?

Thanks
Zohar

[wurlycorner]

Electrovalves on the hydractive suspension.

[Mandrake]

Electrovalves on the hydractive suspension.

Won't be that.

Unless one of the door switches is faulty (which would also bring on the interior light) the electovalves won't activate on their own once the car has been parked and locked for at least 30 seconds.

Even if they did the noise would be a click followed by 30 seconds of whining not a brief hiss.

[Stickyfinger]

Snake Under the Car ?

[Mandrake]

Well the fuel pump priming / topping up does fit the noise perfectly - the only problem is that it shouldn't still be topping up the fuel pressure after sitting for 8 hours IMHO...

Perhaps a fault could cause it to continue to do so though, I'm not sure. Maybe a faulty ignition switch contact or a faulty ECU ?

[wurlycorner]

Unless one of the door switches is faulty (which would also bring on the interior light)

That was going to be my suggestion if it was deemed to be the electrovalves.
My Xantia has a fault in this area - electrovalves operate as they should off the door, but neither of the interior lights work (and no, it's not the bulbs or switch position! ) so random gremlins are possible here (and more likely than a fault causing the fuel pump to operate???)

Even if they did the noise would be a click followed by 30 seconds of whining not a brief hiss.

Ah yes, but one man's whining is another man's hiss?!

I dunno though, I'm much less familiar with these bits of the car than you - only way to know is to hear the noise itself

[Stickyfinger]

This really is the strangest of threads

a little off the wall but :

What about, as the car is in Israel, that as it heats up the hiss is fuel pressure releasing from the Filler cap/Vapor trap (if fitted)