Hey guys, i swapped my 255 walbro fuel pumps with 400's , now the fuel pressure goes below 40 as soon as it sees boost, any idea what could be the problem? i replaced the hobbs switch and nothing changed. fuel filter is very old but i doubt that is the issue.

Thanks

 

-Electrical problem with insufficient wiring
-Regulator not boost referenced
-Second pump not turning on
-Fuel line inside the tank is leaking

My money is on the last one.

 

Same here think you need to check fuel lines in the tank. Seen that happen plenty of times. After that you confirmed that lines in the tank are good check the Hobbs switch and verify the second pump is coming on.