cbaxter

I have a 2000 Expedition, I went to start it and it began making a loud "popping" sound. The sound is coming from the engine compartment, but the exaust from the tailpipe is puffing out in sync to the popping sound, which is 3-4x/per second. When looking at the engine compartment one of the hoses is bouncing and it goes into the enginee block (down from where you add oil). The hose pulls out and has a metal cap like piece on the end, however when you look at the hole where the holes goes, it is threaded, but the metal cap is not.
Standing in front of the car looking at the enginer: It is in the back left section of the engine. The hose enters (connects to the engine) 6-8 inches directly behind the place where you add oil. I think it may be called the header?? The hose then runs behind the engine to the right, but I cant see where is goes. I need help....