Originally Posted by Rzeppa
Update: She took it to a shop today, and they verified that it is indeed running on only 3 cylinders, they pulled the #4 plug wire and observed no change to idle. They also observed a good strong spark there.
So I guess the next step is to pull the injector connector and ohm out the injector. If it ohms out good, I would guess there is a faulty connection to the injector. That would be super cheap to fix if it is easy to find and get to. If it's the injector itself I still have to imagine that would be a bunch cheaper than a new cat. My recollection of pulling injectors is that they can be a PITA and need a flare wrench depending on how they're oriented and what's in the way of getting a socket over them.
Thanks again for all the helpful suggestions!
Couldn't say on the Subaru, but getting to them is a major PITA, actually getting them in and out isn't hard. The fuel rail(s) might be pressurized, I pulled the fuel pump fuse and cranked the engine to release the pressure. Otherwise pretty straightforward. Replace all the copper crush gaskets and rubber o-rings, don't be tempted to save a few dollars. :-)
Might not be any cheaper than a cat. The injectors for the 22R-E list at almost $200 and the good price is about $165. This is for a new part. Hard to say what pick-n-pull or used might be, get a couple used and figure out a way to test them maybe? I just put a Walker cat on my truck, was about $75 from Amazon. If it's like the 80 with multiple special fit ones, then catalytic converters are expensive.