As mentioned it could be a lot of issues, but the Fitech sets codes, look on your controller and see what if any codes have been set, if no codes are set, I would look at ignition system first. The other thing to check is that there is a filter screen on the pressure regulator valve if you take it out. I have had the one on mine get clogged and it caused it to run bad. The injector drivers in the computer will shut down if you have to much fuel pressure, it takes more amperage to lift the pintle off the seat of the injector.