Car is a 2000 si, b16 head, b20 bottom, with a ls/v chrome base map. It is throwing cel 43 which is fuel supply system/regulator. It will only throw the code if you go over 65mph, just cruising around it will not come on, and when it does come on it will go off with with the ingnition and not come back on until you reach 65ish mph. The car runs the same with the cel on or off, it does not mis fire or hesitate when the light comes on.
I have checked the fuel regulator, with the vacuum line on, the regulator i run 45psi and with it off the fuel psi will slowly climb up.
Any help is appreciated

 

help!!!!!!!!

 

Check the primary O2 sensor.

 

thanks