Hi. I'm a big DIY mechanic and have been reading how-to posts on this page for years but have yet to make a post.

I have a 2003 F-150 with a 4.2L. There is a narrow red vacuum line that starts out on the passenger side of the engine compartment and is routed behind the intake manifold until it ends up on the driver side of the truck. Does anyone know where it attaches to? It has a fairly strong suction when the engine is running, but I can't figure out where it attaches.

I will try to post a picture.

 

View image: vacuum

 

I don't have a 4.2 but it may be for the egr sol or evap. If you let the line lay natural it should be close to a barb fitting on a sensor or solenoid.