1991 Dodge Shadow Runs on 3 cylinders

Engine Performance problem
1991 Dodge Shadow 4 cyl Front Wheel Drive Automatic

1991 Dodge Shadow ES 2.5 Turbo. The car runs on 3 cylinders. When we let the car idle it makes a knock noise every once in a while. But when we disconnect the fuel injector harness to that cylinder you don't hear the knock. We replaced the fuel injector and it still runs on 3 cylinders. The car has spark at that cylinder too and it has good compression.