Pretty likely dirty injectors.They will spray crooked, sideways, not at all, and do it in the blink of an eye.It can cause a lot of trouble.I would dump in a few cans of injector cleaner, like chevron techron.It will take some driving for it to work as it cleans when it goes through the injectors.Not while the engine is off, naturally.
I have a five gallon bucket with a fuel pump in it, I mix A can of chevron techron in about 1.5 gallons of gas. Then I disable the vehichle fuel pump, and disconnect the fuel lines and hook to the bucket/pump.Then restart the previously warmed up car, prop the throttle at about 2200- 2400 rpms, and stand back and just listen to it. You will hear the engine misfire then start to clear up, cylinders coming to life and as it cleans the engine will pick up rpms from where you initially set the throttle at. usually takes about 20-30 minutes, to run it through.
It cleans faster than driving, but dosing the fuel heavy with the cleaner and driving for a while should provide results, usually enough for you to dtermine that it is the problem.
The early EFI fords were pretty notorious for having dirty injector trouble.