1997 F - 150
I lost the Cap for the Schrader Valve on the fuel rail. Can I replace it with a cap for a valve stem off a tire?
I am changning the fuel filter and I got one fuel line disconnected no problem, but the other side coupler seems to be seized up. Can I spray penetrating oil on it to loosen it up?

 

The Scrader valve cap merely keeps "crud" out of the valve.I believe the original one had an o ring in it,but any cap will do.Concerning the penetrating oil question,yes...wd-40 comes to mind....