1993 Ford Escort fuel injectors

car ran great till it quit one day last week.
ruled many things out
plugs wires coil pack all ok. gets good spark
fuel pressure on rail is 41psi. had hoped it was pump!
filter new.
injectors not firing for some reason. plugs are dry
how many things control these injectors?
all 4 can't be bad.
going to replace pressure sensor on rail today.
if cam position or belt, wouldn't it not have spark.
is their a "brain box" failing, bad ground wire? i have't looked in a book yet or tried a garage. thanks for help