Cadillac Repair: fuel injecters for a throttlebody, test light, light probe

Question
i have a 89 deville with a 4.5 and one injecter wont work but if you switch the plug from the front injester and put it on the back injecter then that one works and the front one dosent. Put a new ecm in and it still has the same problem but the only code that shows up is E-30 witch is a RPM error to great. and what does that mean to?

Answer
There are 2 wires on each fuel injector.

each one has battery voltage on one of the wires and the other is the ground that is grounded by the ecm to fire the injector.

remove the 2 wire connectors from both injectors and Check to see that each injector has battery voltage on one of it's wires, Then using a test light put the test light ground and the test light probe on one set of the injector wires and when you crank the car the test light should flash ON and OFF. Repeat this on the other set of wires.

If you have battery voltage on one wire of each injector and when you use the test light on each set of injectors and one set does not flash ON and OFF as you crank the car you have an open on the ground wire of the injector that is not flashing.