This might be a silly question to ask. I noticed that in the FASS owners manual that it states not to fill up, with the truck still running. Is this something you MUST not do. Or will it hurt anything if it has been done a couple of times before I noticied that I shouldn't.
thanks

 

On some (or most, I don't know) models, the return from the pump is plumbed into the filler line. So when you're filling up, the air coming out of the return line can cause fuel to spray out, or just stop the nozzle from filling. If you can fill it without any issues like this, I wouldn't worry about it.

 

I think the complete FASS system is the only one that returns into the filler neck. The standard fuel pump, without the filters, does not.

 

Easlier FASS systems installed the pump fuel return line into the filler neck. No longer done that way.
As mentioned...if you can fillup while ideling...do it. No harm done.

RJ

 

Its actually was installed in the fill neck vent tube. This is the one you can not fill with the FASS running.

We now install it into the fill neck and you can idel the truck when filling with this set up.