I just replaced my 1996 fuel pressure regulator with a new BWD regulator. The excellent instructions in https://blazerforum.com/forum/tech-a...agnosis-23038/ say the pressure at the Schrader valve should not fall more than 5 psi in 10 minutes but mine is falling more than that.

The plenum is open and the injector poppets and fuel pressure regulator are visible and did not leak onto the intake manifold at all during the tests. The tests are performed with the engine off (KOEO).

I built a tool that allows me to shut off the fuel lines at the fuel filter or at the return line disconnect. The tool is tested and does not leak.

Test 1 at fuel filter location of isolated fuel pump and check valve ("dead head").
T=0 78 psi
1 minute 74 psi
4 minutes 69 psi
7 minutes 68 psi
10 minutes 66 psi

Test 2: Reran test 1 and bled the air from the gauge this time:
T=0 78 psi
10 minutes 60 psi

Test 3 at Schrader valve of new BWD pressure regulator
T=0 Pump on: 60 psi. Drops to 56 psi immediately after pump off.
Ran test 6 times. Drops to between 43.5 and 49 psi in 10 minutes. Hypothesis: Regulator drops pressure to 56 psi instantly and then check valve releases the rest over 10 minutes.

Test 4: Shut off the fuel return line to see if regulator is leaking into return line. No effect. Pressure at Schrader valve drops to 49 psi in 10 minutes. Performed twice.

Test 5: Maybe loaner pressure gauge is leaking. Got new loaner pressure gauge. Feed and return lines are open. Schrader valve pressure goes to 62 psi while pump still on, drops immediately to 59 psi at pump shut off and then drops to 52 psi in 10 minutes. The pressures are about 2 psi higher probably due to change of pressure gauge, but it still drops over 5 psi in 10 minutes.

Test 6: at Schrader valve with feed and return lines open. 58 psi to 47 psi in 10 minutes.

Test 7: Close off feed line at filter after pump stops. Result: 56 psi to 44 psi in 10 minutes. It drops FASTER with the feed line closed off.

Test 8: Did I get a bad new regulator? Buy a new GP Sorensen regulator and try that. Test at Schrader valve with feed and return lines open. Drops from 56 psi to 34 psi in 10 minutes.

Test 9: Shut off the feed line after the pump stops to confirm the new regulator is leaking. Schrader valve pressure goes from 56 to 43 psi in 10 minutes. It dropped half as much as test 8, so that confirms both the new regulator and check valve are leaking.

Test 10: Keep feed line open after pump stops to see if test 8 results are repeated. Result: pressure drops from 56 psi to 46 psi in 10 minutes. Results are different from test 8.

Frustrated. Test results seem to conflict. Can you draw a dependable conclusion from all these tests?