So I have recently purchased a 2000 xjr. Adding to my list of jags. I do not have a boost gauge or a scan tool that reads boost. I feel like it is lacking though.
what are the main issues that would cause low boost ?
SC sounds fine no loud noises.

thinking about a sc pulley upgrade as well but I want to make sure I am getting full boost before I go that route.

with 100k in the sc am I asking for trouble with a pulley spinning the old SC to an early death ?

 

The first thing to check is the bypass valve. It is located on the intake elbow connecting the throttle body to the supercharger. Not easy to see and you may have to remove the TB to inspect the valve.



The valve is spring loaded and kept in closed position (maximum boost). With the engine running, if the intake vacuum is high (idle or cruise), the vacuum actuator will pull the valve open and reduce the boost; on acceleration, when the intake vacuum drops, the vacuum actuator will release the bypass valve towards its closed position which will increase the boost. If your bypass valve has seized in the open position, you will have much reduced boost. Check whether the valve is fully closed when the engine is off and whether you can move its lever against the spring towards open position and whether it returns smoothly to the closed position when you release the lever..

 

thanks this will be very helpful.