Volvo petrol vent system

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Wed 6 Mar 2002 08:31
Volvo petrol vent system - andy sampson
I have a 1991 Volvo 480 Turbo, Looking into why when I remove my petrol cap I hear a long hiss. Has anyone had any probs with the tank vent system, the vapours are pulled from the top of the tank and passed through a charcoal filter and then burnt by the engine via the inlet manifold. The vent line consists of a gravity valve (I would think that this prevent's the tank emptying if the car rolls over) and a diagphram valve, I am thinking that if the diagphram valve is passing then the turbo pressure within the inlet manifold will pressurise the fuel tank?????. If this is happening how would this affect the running of the engine?, the tickover is very lumpy but only when the tank is less than half full of fuel.

Anyway before I start ripping things to bits just finding out if anyone has experiance of this system and common probs?

Thanks

Andy
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Wed 6 Mar 2002 08:49
Re: Volvo petrol vent system - Jonathan
My car does this also.

I thought that it was positive pressure in the tank to assist in drawing fuel into the system. I dont think its anything to worry about. (I really shouldn't say that should I)!

Jonathan
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Wed 6 Mar 2002 10:37
Re: Volvo petrol vent system - Dave N
Try a message on the forum at www.volvoclub.org.uk
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Wed 6 Mar 2002 11:15
Re: Volvo petrol vent system - Richard Hall
My (non-turbo) Audi does exactly the same thing, and it appears to have no effect on performance, idle or anything else. I can't tell whether the hiss is due to pressure or vacuum, but as long as the car runs, and the fuel tank doesn't explode or collapse, I'm leaving it alone.
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Wed 6 Mar 2002 18:09
Re: Volvo petrol vent system - Adam Going (Tune-Up Ltd)
Andy,

All modern vehicles have a similar system. The tank venting into the inlet only occurs under certain driving parrameters. At other times the fact that, as in all injection systems, fuel is returned to the tank under pressure will inevitably cause some pressurisation of the tank. So, unless there are other problems, your situation seems normal. The lumpy idle when less than half full is very strange, though. Suggest you check fuel for airation when level is low by fitting a length of clear plastic pipe on the delivery side of the fuel rail - any air in the delivery could suggest a damaged pick-up in the tank.

Regards, Adam.
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