Recently did the oil pan on my rx7. After I started to put oil in, I noticed the hose under the filler neck came off. Where is that hose supposed to go?

 

Download the Factory Service Manuals (FSM) they have hose routing guides.
there are 2 hoses by default in stock engine. 1 near the top by the oil fill cap and another near the base close to the housing.
each have different functions. upper is emissions, lower is for oil that is pushed up the filler neck and routes to the charcol canister.

 

That hose connects to one end of the PCV (Purge Control Valve), which is a small plastic valve that is vacuum controlled. The other end of the PCV connects to the intake manifold. The PCV is an emission device that basically recycles engine blow-by back into the combustion chamber.

 

Is it possible that the PCV could have broke off? How far under the intake does it go?

 

The PCV is connected to the oil filler tube with a short (~6") rubber hose. Here's a link with a photo of the PCV valve (https://www.atkinsrotary.com/store/7...0-20-950A.html). The larger nipple connects to the oil filler tube. Not sure were the smaller nipple (on same side) connects to but it looks like to the intake. The single nipple on the other side connects to the dynamic chamber. Attached are a couple pages from the '89 FSM with an explanation/diagram.