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Yes, normal, but can seem scary to those who don't know, particularly when the car has a very empty tank, considerable vacuum pressure builds up inside. They used to have a name something like "foo-foo" valve on old Toyotas which had a special valve to let the pressure out when you twist the cap. They used to call it a foo-foo valve as the hissing noise "used" to make a similar sounding noise.

Remember, you've got a large tank when empty (85 litres).

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  • 2 weeks later...
They used to call it a foo-foo valve as the hissing noise "used" to make a similar sounding noise.

LOL - a "foo-foo valve" is a common term used to describe something that doesnt really exist / name unknown etc only ever heard it in context to aircraft!

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Some of those definitions are just mental!

And not quite on topic but yeah, my fuel cap makes the noise too - it's a good time to let one go and everyone just thinks it's the fuel cap :whistling:

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Sorry Colin, I have to disagree!

On my LS400 '94, I have to hang on to the cap (a little exagerated but not much!) to stop it being blown across the forecourt. If it was a vacuum, then it would be difficult to remove the cap!

Surely the pressure is there to aid in petrol delivery to the engine, a partial vacuum would do exactly the opposite.....

Cheers

Dave

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I think the EEC system works differently on newer models which is what my link describes. On older systems the tank can have +ve and -ve pressure at certain times. Check valves in the system should prevent either condition getting excessive.

+ve pressure is controls by check valves in the fuel cap and one of the valves in the charcoal canister. -ve pressure is controlled by another valve in the charcoal cansiter.

If you are getting excessive pressure then you should get your charcoal canister checked.

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  • 2 weeks later...

thank you, so where is the EECS then?? near fuel tank, exhaust, throttle? on the shelf in the garage cos they forgot to refit it?? :lol:

talking of which, my garage, after an oil and auto fluid change 'lost' the under-engine protection sheet (fibreboard i guess) and when i asked them to re-fit it, they claimed it was never there! so if you're thinking of using a garage in newbury for your vehicle repairs, PM me first to check that it's not the one i spent £4,000 with!

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