P0455 in ‘03 Expy

I was pretty sure I was a member here but had to create a new account?
Anyway....
‘03 200,000 miles.
Just replaced the fuel pump about 2 months ago and started getting P0455 code.
Purchased a new fuel cap (not original clicky one but the quarter turn Ford one) and code went away.
About 2 weeks ago code returned again.
Sooo,
What should I be looking at?
Easiest to hardest I guess:
Is the quarter turn Ford fuel cap not the correct one?
Checked all under hood solenoid hoses and sprayed started fluid around to hear for idle increase. Not able to find a leak or cracked/broken hose like I have in the past. Large leak so I checked manifold hoses etc and no go.
Solenoid in rear is a bitc$ to get to but not sure if maybe that is it?
Ugh...I don’t wanna drop the tank again BUT could I have not replaced one of the hoses to the top of the tank or even sealed the tank gasket properly? Pretty sure I was very careful about sealing it all back up but you never know.
Wifey doesn’t wanna drive the truck at all until it is fixed. I told her it’s fine to drive but I’ve told her to never drive with engine light on so she is doing what I told her
Any thoughts/suggestions? Truck has been really good to us. Synthetic from the start and I’ve kept up on all maintenance.

I’d change the fuel cap again. I had an aftermarket cap fail on my 95 F150 at the emissions station test. The funny thing is I have dual tanks and the front tank still has the original Ford cap and it passed their vacuum test. The newer aftermarket cap on the rear tank failed.

Smoke tester would come in handy troubleshooting this.

https://www.amazon.com/AutoLine-Pro...907404&sprefix=mechanics+smoke,aps,157&sr=8-2

The replacement cap is an actual motorcraft cap but it’s the 1/4 turn and not the original ratcheting cap...
The smoke tester would be awesome. I could use it for kids parties afterward.
Amazing avatar
oo

i had a bad relay when this happened to me

What relay are you referring to? is there a difference between the 2 fuel caps? New One is push lock and 1/4 turn.
Old one was turn until it clicked or ratcheted...

Erased the code a month ago and it hadn’t returned. Ok so today it’s back again
P0455.
Just to recap. I replaced the oe motorcraft fuel cap with a new oe fuel cap but it isn’t the ratcheting one but the quarter turn one. I would assume it’s fine?
I did notice when I took the cap off around the rubber seal was a wet substance. Smelled it and it seems to be fuel.?
Fuel tank is only 1/2 tank so it’s not sloshing up around the cap...a bit confused here.
Can someone help a brother out?
Wife is ready to take it to the stealership man-I don’t want that!!

A smoke test machine would really help with your trouble shooting. But easiest part to repair / replace is the control solenoid there under the hood. That controls the whole evap system, and a blown diaphragm in that solenoid will produce the P0455 gross vacuum leak code easy. After that you just have to inspect all the vacuum hoses going to the charcoal cannister there above the spare tire.

Smoke machine ....
https://www.amazon.com/AutoLine-Pro...s+smoke,aps,157&sr=8-2&tag=expeditionforum-20


Evap Control Solenoid....
https://www.amazon.com/Motorcraft-C...words=Motorcraft+CX1597&qid=1619311748&sr=8-1

Ohhhhhh I see! I actually took both of those off. The one on the brake booster and there is another one near the drivers side fuel rail. I popped the top off of it, cleaned the filter out and put it back together.
I’m kind of thinking of starting at the rear end and taking the damn charcoal canister assortment out above spare tire and checking to see if the “flap” may be stuck. There is also a solenoid that may not be functioning properly.
Again, is she able to drive the vehicle? She sees a cel or mil and immediately assumes she cannot drive it. I taught her that though...
Car has been well maintained. 200,000 miles and running very well. Thank you for your help! Again, great avatar

So today I dropped the rear section (NOT easy and a few curse words)
I found 2 canisters, a solenoid (a bit rusty) and the plastic lines running up to the engine bay.
Is there a way to test the rear solenoid? I plugged it in and started the engine. I felt no pressure or suction from the plastic lines or solenoid. Should there be?
I also took off the evap solenoid under the engine bay and cleaned it out with carb cleaner. Blew in the one side and air came out. Blew on the other side and it did not come out....
.?