I got a check engine light and found a P0440 code had posted checking with an ODBII scan tool.I searched the other P0440 related posts, but no one had the additional symptom I have.
I occasionally hear a muffled sound when I start the car that sorta sounds like the engine may be backfiring into the intake manifold or through the throttle body. I only notice it if the car has been running a while, gets shut off for 5-10 minutes and is restarted. I had the fuel pressure regulator replaced under the recall last year. I also pulled the vacuum line to the new regulator while the car was running, but I didn't see any gas or smell any gas fumes (thinking maybe the regulator was replaced with a faulty one).
Does this point more clearly to the gas cap, evap canister or something else? Thanks for any help.