How do I know when to replace the fuel filter?

That's easy. When a hole rusts through it and starts spewing gas, that's when.

 

[BigRondo]

That's easy. When a hole rusts through it and starts spewing gas, that's when.

I'd say that's a good sign. You may have jinxed it with your log in name though! :

 

[RustySJohnson]

I'm afraid that's my real name!

"log in name" :

but I don't have red hair.

 

[BigRondo]

But you did have a rusty fuel filter!

 

[ramren16]

just put duct take on it, it will be good as new

 

[RustySJohnson]

....and, how do I know when to replace a Fuel Injector?

Same way I know to replace the filter, when it spews fuel.