[Jim Doak]

If you have a liquid-filled gauge just be aware that the gauge pressure will change (drop) as the gauge temperature increases. (Not that the actual fuel pressure is dropping, just the pressure displayed on the gauge.)

I've learned this recently from chasing an actual fuel delivery problem. It's caused from the gauge referencing the pressure within the gauge liquid instead of referencing atmospheric pressure.

If you have a liquid-filled fuel pressure gauge located in your engine compartment you can perform a little experiment like I did. Check your fuel pressure when you first start your engine then check it again after the engine compartment has warmed-up. If it reads lower when hot as compared to cold, with the engine running pour some cold water over the gauge and check the pressure. You may be surprised and see the displayed gauge pressure increasing as the gauge temperature decreases.