Fuel pressure

[DCGN]

My fuel pressure gage on the fuel rail shows a 5 psi difference between when it is cool under the hood and when it is warmed up. I set the static pressure at 45 psi when the engine was warmed up and it shows 50 psi when cool.
I also have a gage mounted on the hood. They both read the same when cold. But when the engine is at full operating temp the gage on the fuel rail reads 3 degrees less than the external hood gage. Has anyone else experienced this?

 

[DCGN]

Anyone?

 

[my1stgn]

If you say your seeing a psi difference in fuel pressure when the engine is cold and when its hot then thats normal. Engine idles higher when its cold to warm it up and get in closed loop sooner and get the cat warmed up and operating. When you increase engine RPM you decrease engine vacuum so your fuel pressure will go up. Once your car gets warm your idle lowers and vacuum increases so your fuel pressure drops a little. Not sure if thats what your asking or if this answers your question?

 

[DCGN]

My1stGN, thanks for your reply. No, that's not exactly what I'm talking about. I can start the car in the garage with the hood up and let the engine warm up to 170 deg where the thermostat cycles, then set the static pressure @ 45 psi. I can then take the car out and drive it for a while, come back and check the pressure at the fuel rail gage and the static pressure will read about 40 psi. This is a liquid filled gage which I have checked to be accurate. I just don't know why the under hood heat affects it so much.

The question is, should I set the static pressure before I drive the car, or after when the engine compartment heat is higher?

Thanks,

Dan