what is the fuel pressure for 2002 lincoln ls v6 ?

I believe most modern Ford use 40psi at the tip of the injector.

so... if you are measuring rail pressure - it will be lower (depending when you measure it) - it will be 40psi - the manifold pressure (or vacuum). So at idle, you'll get about 18hg-20hg of vacuum (roughly -10psi) - so the rail pressure will be closer to 30psi.