Po440 98 5.7l

[Markus Escamilla]

I got a po440 code and i replaced the gas cap and the service engine light went off. A few weeks later it comes back on again. The fuel pump is new so i figured that sensor is fine. Po440 is the only code being thrown so what could this be ?

[davester]

google the code and go through the whole diagnostic procedure for it.  It is more than just "replace gas cap".

[Brian Lindsey]

dave is correct , you have a large leak ,  check for broken evap lines, , then remove your purge valve and blow through it both ways, next do a continuity test on vent valve , purge valve is always closed and vent valve is always open  .good luck