I have had bad gas mileage and hard starting with my 3.4 DOHC so I decided to test for leaky injectors. I hooked up a pressure gauge to the fuel rail and I have 41 psi with the pump on 38 with it off. I left the gauge on for about an hour and it read 20 psi. Is the pressure supposed to drop like that over a long period or do I have a problem? How long should the fuel rail hold pressure?

Thanks,

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Chris

3.4 TDC SWAP COMPLETED...this is going to be a fun car

The fuel rail should hold pressure for a while but it doesn't stay high forever. After the vehicle sits for a while some of the fuel eventually works it's way back to the tank, perhaps through the fuel pump . If the pressure drop takes an hour to happen I would believe that you don't have a serious injector leak. When injectors leak my expereince has shown that they usually leak down faster than you've indicated.
The way to determine if you have a leaking injector is to use an injector tester that pulses them and a pressure gauge connected to the rail. . You pressurize the fuel rail measure the pressure, then the injector tester is attached to the injector plug and one injector is pulsed. You then take a pressure reading to see how much the pressure has dropped. You make a note of this, repressurize the fuel rail and go to test the next injector, pulse it with the tester and againmake a note of the pressure drop.. Continue this for all the injectors. If one injector causes a large a difference in the pressure drop than the others do, it is considered to be leaking. But before we get to this, it might be a good idea to check the ignition first.