Little green cap?

[06FordFX4]

What is this thing? It was unscrewed so I screwed it on. What's it do? And is it sposed to be on or off? Been off since I got the truck, just figured I'd screw it on.

Any thoughts?

 

[fomoco]

a pic would be nice

 

[Diablo]

it keeps the little green things in

 

[06FordFX4]

ah ****. damn tapatalk has been ****ting the bed lately with pictures.
hang tight

 

[06FordFX4]

here ya go.

 

[fomoco]

that's to turn on the nawsssss!!!!.... I've never noticed it on my truck

 

[klinger86]

Looks to me like its a dust cap. Leave it on or take it off I don't think it will hurt anything.

 

[djfllmn]

that looks like a vac. test port

 

[rwenzing]

The green cap covers the port used to check the fuel tank and evaporative emission system for leaks. Keep it on.

 

[06FordFX4]

Interesting. Good to know. Wonder why it was off....

Been off for at least 30,000 miles haha. It's on now though.

 

[rwenzing]

On most vehicles, that port would rarely or never be used. Normally, the cap would be removed only as necessary to leak-test the evap system by injecting smoke into it. The usual reason to suspect a leak is a CEL and corresponding trouble code.

 

[06FordFX4]

Thanks for the info sir.

 

[Belvader]

I vote it keeps all of the rainbows and pretty unicorns and cupcakes stuck inside... but that's just me