Hi, I have an '86 Australian V12 XJSC, which whenever I open the petrol cap,
releases a huge amount of pressure. Open the cap (hot or cold day, full tank
or almost empty) and there is a big whoosh for a couple of seconds. A bit
embarrassing at the crowded petrol station!

I understand we need pressure in the tank to prevent vaporisation, but too
much will cause petrol leaks, whilst too much of a vacuum is not good for
the tank nor pump either.

Just wondering if anyone else with a similar car (I.e. emission set up) has
the same experience when opening the cap or is it just mine? If so and you
fixed it, what did you find?

Thanks all,
Nick.