Xantia V6 fuel pump running when the car is off!

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Mandrake
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Xantia V6 fuel pump running when the car is off!

Post by Mandrake »

Hi All,

Here's a strange one! :?

It's -7C tonight and I went outside late at night to unplug the Leaf from the charger and heard the sound of a pump continuously running and initially assumed it was the coolant pump in the Leaf, but no, it kept going after I unplugged the Leaf and didn't seem to be coming from that direction anyway.

After looking around a bit I realised the fuel pump (inside the petrol tank) in the Xantia was running continuously while the car is off even though it hasn't been driven for more than a week! :shock:

I popped the bonnet open and sure enough I could hear fuel running through the fuel rail. Fortunately I had a 12v battery charger connected otherwise I think it's very likely that the battery would be flat now as I remember hearing the same noise last night as well!

As soon as I turned the ignition key on the pump stopped, I started the engine and turned it off again and the pump is not running. So what on earth is happening ?

I should point out that the engine ECU does have the ability to run the fuel pump when the key is off and the car is locked by turning on one of the two big relays in the ECU box - in fact it's normal for the fuel pump to come on for about 2 seconds a minute after the engine is turned off, and then a few more times for 2 seconds a piece over the following 15 minutes or so.

This is done to help avoid fuel in the fuel rail from boiling due to sitting above a hot engine without recirculating just after the engine is turned off. (Although it doesn't really run for long enough to do this effectively and some boiling still happens...)

However I've never noticed the fuel pump running continuously and for so long with the car off before - it was running when I came outside and for the few minutes that I was looking around for the noise.

Is this some kind of automatic freezing protection to prevent the fuel in the fuel rail from freezing in sub zero temperatures by periodically recirculating it ? If so running continuously is just going to run the battery flat, I would have thought it might run for say 5 seconds once every 30 minutes or something not continuously, and I have not seen any mention of any freezing protection for the fuel system in the service data.

Has anyone had this happen before ? This could certainly explain why I've had flat batteries in winter before... :?

Are there any risks (like fuel lines freezing) to leaving the car unused for a couple of weeks in continuous sub zero conditions even with a battery conditioner connected to maintain the 12v battery ?

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Mandrake
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Re: Xantia V6 fuel pump running when the car is off!

Post by Mandrake »

Just went outside to check before bed and the fuel pump is running continuously again!!

I popped the bonnet and the still connected 12v battery charger was reporting only 11.9 volts as despite its best efforts to keep the battery topped up the fuel pump is drawing enough current to discharge the battery, at least partially. (Maximum charge current from the charger is about 5 amps)

I turned the key on and off and it stopped again. Hmmmmmm.

Armidillo
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Re: Xantia V6 fuel pump running when the car is off!

Post by Armidillo »

Better disconnect the battery to let it recharge, while you sleep on the problem!

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white exec
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Re: Xantia V6 fuel pump running when the car is off!

Post by white exec »

Freezing point for petrol (complex stuff) usually cited as -40 to -100°C, so not likely in UK.
The component in it most vulnerable is any water present.

wheeler
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Re: Xantia V6 fuel pump running when the car is off!

Post by wheeler »

Could this be a sticking double relay or has it got moisture in it? The next time it does it I would try giving the double relay a tap with the head of a screwdriver to see if it stops. Might also be worth unplugging the ECU to make sure there are no signs of water in the plug. Failing that you will need to get a wiring diagram & see if the ECU is sending the command to operate the relay.

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xantia_v6
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Re: Xantia V6 fuel pump running when the car is off!

Post by xantia_v6 »

The wiring diagrams for a mk1 V6 Xantia are:

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