My 1998 XK8 (X100) convertible has petrol forced out past the fuel filler twist cap seal if speed in excess of 40mph. Not a massive amount but it finds its way out of the fuel cap area drain pipe to atmosphere and the smell of petrol is very obvious when the convertible hood is down. Have tried a known good filler pressure cap to no avail. I have read the available information on the fuel supply system being pressurized and 'excess' fuel returned to the fuel tank. There is mention of a ' purge valve ' situated in the nearside front wheel inner wing area and a pressure relief valve on the fuel tank. I have asked two local jaguar repair specialists if this is a known problem and the answer was NO. Anyone met this before ? Here's hoping, David Jefferson.

 

I know its an old thread, but did you ever figure this out?

 

Yes it was solved by jagtech in stockton, the rochester valve was 'modified' in their words.

 

They modified it or it had been modified before?