I've been having a number of issues that led me to the FPR leak down test. With the original FPR, key on for 2 seconds, the pressure was 51lb and when the pump kicked off, the pressure dropped to 46 lbs. After 10 minutes, the pressure dropped to 36 lbs (once to 20 lbs).

I repeated the test several times and sometimes the pressure dropped to only 41lbs per spec, but other times to the 36lb range. I tried gently tapping the regulator while it was leaking down, and I saw it drop 5lbs and with a little more tapping, another 5lbs so I replaced the regulator.

With the new regulator, when I turned the key on for 2 seconds the pressure went to 51, but when the pump kicked off, the pressure immediately went to 20 lbs. I tried it several times with the same results (car starts OK). My question is did I get a defective regulator or is it exposing symptoms of another problem (leaky injector or bad pump)?

Without the proper shutoff tools it would be tough to say if it'* the regulator, an injector or the check valve in the pump.

An injector would fill one cylinder and you should be able to read that on the plugs.

Pump check valve vs FPR would be tough to figure out w/o the tool. ...unless you rig up a way to check the pressure before the rail. Then letting it sit and watch how much it drops.