Jaguar Repair: 1997 XJR Vacuum in fuel tk, charcoal canister, manifold vacuum

Question
When the car is on the road I get quite a lot of vacuum in the fuel tank and whilst the car has been away for the winter months in a heated garage the same think seem to be happening when I check on the car each month (car has not been run whilst in storage but still get vacuum).  So my question is is this normal for these Jaguars or should the Purge valve not take the vacuum away or are these cars always under a slight vacuum, even when the purge valve is working correctly.  If it is the purge valve is there any way to check it to see if it even working or not..

Answer
Hi Bill,
I have no experience nor info on any Jaguar after the 1987 models. However, no car has vacuum in the fuel tanks that I know of. It is pressure not vacuum. The earlier Jags use about 3 PSI in the tanks and a small pressure valve regulates that into a charcoal canister and a purge valve uses manifold vacuum to purge the canister in an attempt to remove escaping vapors.

You need to read the profile of each tech to try to locate a tech for later model Jaguars as to how they are set up as to the purge valve and pressure valve.

Howard