I have a mech fuel pressure gauge mounted outside the car, after running for a while it will read 40~ psi at idle and 38~ psi cruising, goes up to around 43 at WOT though. pressure will immediately bleed down about 15~ psi when car is shut off. is this out
of the norm?

shouldn't fuel pressure always increase with throttle?

also a few months back when I went to get my car dyno tuned after the cam swap it was going lean on the nitrous. is this a sign of a failing fuel pump? car doesn't have starting issues

 

Those numbers are all within the norm. The pressure going to 43 psi at WOT seems that your pump is operating fine. The immediate bleed off of pressure is not fine. You may have a rip in the diaphragm of your fpr, or your check valve for your pump isn't working...need to diagnose it.

Pull off the vacuum line to your fuel pressure regulator, if you see fuel in the vacuum line, you have a faulty regulator.

 

The FPR does not actually vary pressure. What it does is keep pressure constant as compared to manifold vacuum. Understanding that should help you understand the readings you see.

As said the numbers you are seeing seem pretty normal, but the bleed down is not.

 

so check the fpr and how to i diagnose the check valve in the fuel pump?

 

Courtesy of Shoebox:
http://shbox.com/1/4th_gen_tech2.htm...essure_testing

Can't tell you how helpful that site has been to me.