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Fuel pressure

Ait

By Ait,
in General Maintenance

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The Tool Enthusiast

The Tool

Posted
Posted

I don't know for sure, but from my (limited!) understanding of high school chemistry, if the temperature drops (i.e. overnight) the fuel (in vapour form - it's not always liquid) slows down thereby reducing the pressure.

Same sort of thing as tyres when they heat up - pressure rises.

Somebody correct me if I'm wrong but it seems logical to me...

:D

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blind_elk Grand Master

blind_elk

Posted
Posted

If the fuel pump runs all night. then the fuel pressure shouldn't drop. But it doesn't, so the pressure drops.

Really got nothing to do with high school chemistry. You lose pressure because the fuel leaks back past the non-return valve in the pump. I have found it normally takes less than an hour for the pressure to drop to nothing.

That's why the ECU runs the pump for about 5 secs before you start - to get fuel pressure back into the lines.

The fuel is always in liquid form. The car won't run on fuel vapour. (Except LPG, before any smarty pants attack me). If you were old enough to have owned a car with carbies, then you'd know that to be the case.

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