1989 Ford Probe Puzzled?

My dad is helping me with repairs he has a lot of experience with repairs but mostly on much older vehicles and is currently stumped by what seems to be some kind of fuel injection issue. The engine turns but the car wont start. We checked the fuel inertia switch it was entirely removed it appears by a previous owner and the wiring bypasses it. The car has run for months without it. He re routed wiring for the fuel pump as it wasnt getting power at first but its now working at the car still wont start. We checked the fuel pressure and it is adequate as well. He has been able to start the car by directly sparaying starter fluid into it but as soon as he stops spraying it stops running. Any ideas where to look next for the issue? Injectors? And how are those tested?