Low fuel pressure after making pass down track

If the gauge doesn’t have an equalization valve on it, with it being above the engine the heat will cause the pressure in the gauge housing to increase. This will increase the pressure on the outside of the bourdon tube that actually causes the needle to move. This will cause the gauge to read low. I use an aeromotive gauge that is liquid filled with an equalization valve. I’m also going to make another suggestion. Having the gauge over the engine with all the vibration isn’t a good idea. I’ve had one fail mounted that way and spray gasoline all over. That with a hot engine could be a mixture for disaster. If the regulator is mounted on the inner fender or some where off engine put the gauge on the output side. Better yet set the regulator and remove the gauge. Here’s a good read.

Fuel Pressure Gauges - Aeromotive, Inc