02 TRD 3.4 auto Evap system

Truck with over 200k. Getting a P(mumble) code now and then for the Evap system. Just annoying at this point, but I would like to fix it eventually.

Short story, was getting several codes, all for evap, changed the gas cap and all went away but for the one that keeps coming back. I notice that when I fill up, the tank never seems to have pressure in it, which I think is not right.

The frame was replaced as well as the tank and filler neck. I've done a quick check for loose/cracked hoses and found nothing obvious. Today while doing oil/filter poked around a bit. Found the switching valve and hose clamps pretty grungy, but seem OK.

Then I noticed these two hoses with caps on them, that "dead end" near the fender well under the master cylinder. Picture is attached. One of the caps spins freely, the other is "tight". Anyone know what they are?

 

Those are breather

 

Those 2 are your trans and front diff breathers, unrelated to your evap. I would try and free the stuck one if you can. If not, replace it

I had identical symptoms and a very consistent P0442 and sporadic P0446 code. I had the overfill check valve and gasket replaced and that took care of all my issues. Tank gives that nice hiss when I open it to fill up indicating that it's holding pressure now. Your leak could be in a different area though, so before you start throwing parts at it I would have it smoke tested.

 

I managed to free them up.

Anyone know the part numbers of the solenoid valves? The truck is 4WD. I see the canister seems to be different between 2WD and 4WD. so I would assume those parts are different also.

I built a "smoke generator" but have yet to smoke test the truck. I was hoping to find a used gas cap I could adapt but may have to settle for some other means to seal the smoke generator to the filler neck.

Or is that what that screw on cap is for, the one under the hood that says evap test, "something", pressure only?