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Thread: Vacuum build-up in fuel tank (1.4 petrol)

  1. #1
    Join Date
    Oct 2013
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    London
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    253

    Vacuum build-up in fuel tank (1.4 petrol)

    The fuel tank on my 1.4 AUA petrol (X-reg) has been developing a partial vacuum as fuel is used, evidenced by the fact that when the cap is opened after a tank-to-tank brim, petrol vapours will vent out of the tank for at least 15 seconds (displaced by nearly 35 litres of incoming/mixed air), whilst at the same time the decompression of the tank can be heard and felt through the chassis of the car during the tank in-breathing.

    I've had plenty of other A2's and other petrol and diesel cars to recognise that this is not the initial one or two second venting (out-breathing) that might happen on a hot day.

    The lack of pressure which can develop in the tank has also caused fuel supply problems - on occasion the car would not pull cleanly between 1.5k and 4k rpm after an EML was triggered, which I was able to resolve (at partial tank level) by stopping the car, opening the tank cap, and allowing normal atmospheric pressure to be restored.

    So, I'd like to understand - what are the designed routes for atmospheric air into the tank during normal operation? Is it through the fuel cap (I have a fuel cap from a 1.6 petrol, but would assume they're the same), or is there also another breather (but not vent) pipe - and if so, does the breather work passively (and so may be blocked) or actively (e.g. by a solenoid)?

    Thanks!

  2. #2
    Join Date
    Aug 2015
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    There is a vent on the petrol 1.4 A2s ive seen, you would have to remove the driverside rear stone guard to be able to gain access to it as attached to the filler neck below the cap assembly , it is a rubber valve cone shapped and conects to a fuel pipe thats conected to an outlet on the top of the fuel tank , im presuming this is the tank breather ..

  3. #3
    Join Date
    Oct 2013
    Location
    London
    Posts
    253
    Thank you, I'll post up once it's been seen by a mechanic

  4. #4
    Join Date
    Oct 2013
    Location
    London
    Posts
    253
    Quote Originally Posted by sailesh View Post
    Thank you, I'll post up once it's been seen by a mechanic
    Solved! For some reason, the breather pipes had been incorrectly fitted by a previous mechanic

  5. Users that liked this post:

    chubbybrown (21-03-2017)

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