fuel pressure drops when engine gets hot

[Jaydog]

I set my base fuel pressure when my engine was cold at 43.5. Once my engine got warmed up it was fine. I shut it off for maybe 30 minutes and started it up again and it only read 39. This is with the vacuum line off and plugged of course. Should I be setting it with the engine warmed up?

What gives?

 

[zfanatics]

Make sure your voltage at the pump doesn't changed once the engine warmed up. That would affect your fuel pressure.

 

[steve]

Make sure it isn't your gauge that changing it's reading and not the fuel pressure.

When reading fuel pressure, keep in mind that a fluid filled pressure gauge will change it's reading as the temperature of the gauge case changes (Under hood temperature). Because it's sealed to contain the liquid inside, a liquid filled gauge no longer compares line pressure to actual atmospheric pressure, reporting the difference. Instead, it compares line pressure to the pressure inside the gauge case. As the liquid in the case heats or cools, it expands and contracts, causing case pressure to change as much as 1 psi for every 30 degrees temperature change of the gauge.

 

[Jaydog]

Good point. It is a liquid filed gauge. Thanks