Apologies in advance for the non-Toyota question, but my daughter has a new-to-her 1995 Subaru Legacy that she can't get through emissions. Her main ride is a 1984 FJ60 so please give her a pass...
I don't know the exact miles but they're fairly high. She got the car for $50, non-running. The symptom was it had died on the PO and wouldn't start, even after the PO had installed a new starter and battery. My daughter put in a new alternator and serpentine belt and it still wouldn't start. I came down and diagnosed bad battery cables. New cables and she runs great.
She failed emissions the first try, passed HC and CO, failed NxOx by about 7 out of 2.5. I followed the manual to test the EGR valve working properly and the EGR pipe is not clogged. The valve operates properly when commanded by the ECU and the engine stumbles properly when the EGR is manually operated with an external vacuum.
There is a CEL code indicating "open injector on #4". There is no obvious indication of any malfunction of the fuel injectors, and my reasoning is that even if she is only running on 3 cylinders that if the injector was not opening to let fuel in then it would not likely create NxOx. No combustion = no pollution, right?
We changed the oil and filter, and air filter last night and now she fails by 5 out of 2.5. My gut suggests that it might be a depleted cat.
My understanding of NxOx is that it is caused by excessively high combustion temperatures, and that the EGR reduces the combustion temperatures by diluting the fuel air mixture with spent exhaust.
So, my question is, IF (and that's a big if, the car seems to run fine) one of the 4 fuel injectors is open electrically and is not opening, could that cause NxOx failure? Or is it more likely a depleted cat? Or maybe something else.
Passing CO and HC seems like a huge deal in terms of eliminating a bunch of stuff.
TIA for any advice. Her paper tags expire on Friday and she's anxious to get this figured out.