Hi, I'm afraid I have still not got to the bottom of this, it has just become less frequent. I am getting more convinced that it's a wiring problem, but anything I've tried has just made it go away temporarily. Luckily I only need it to run on petrol long enough to change to LPG, so I haven't really prioritised it too much.

 

Update from a new member: I have the same problem on my 2003 XJ6 (3.0 V6) running on LPG. I will be installing a fuel returnline this month. If this eliminates the problem I will let you know in this thread.