If, as you say, you had a 2.3 injector then you had the wrong size. You need, as you have discovered, a 2.1 (most likely properly installed on your other unit) in order to work.
The 2.3 nozzle works from 4 to 6 GPM on 50' of hose. If you are longer it will not work.
The 2.1 nozzle works...