89 Dakota 3.9. I put back the stock cap. Had a locking cap on there. Never worked right and the fuel door area was always getting black around it. Now, whenever I fill up, big release of vapor buildup. Did not do it with locking cap and can't remeber if the stock cap did it before. Do I need a new cap, or it it normal?

the black is a mold from the ethynal in todays gas. it lives off the fumes or something like that. grows where fuel is vented or around the filltube.

I have to wash my yellow truck often to keep it off the front fender on driver side where my fuel reg is mounted, my nice shiny braided hose is now a dull growing black fungus looking crap. my alum fuel cel is turning black from it.

kinda hard to kill off unless you go back to non-ethynal gas...then it will slowing die off. from what I have read anyways????

sound like you need a vented cap and have a non vented cap on it.

the tank vent could be pluged if it does not have a vented cap when new.

Your evaporative emissions control system must be plugged. Vented gas caps disappeared on new cars decades ago, way before 1989.

R.

That's funny, my 92 Dakota started doing that recently
And yes there is black around the filler cap area

Putting back the locking cap until I figure it out.