Injectors wont fire on start up and cuts out at certain RPM.

If you have not verified that the injectors are not firing, it is just speculation at this point. When it won't start, you can isolate what is not present by first checking for spark at a plug or two. If there is spark, spray some carb cleaner, or other accelerant(starter fluid) in the throttle bore. If it fires, you have a fueling concern. Next would be to check for fuel pressure. This all can be streamlined at the time of the no start, by installing a spark tester, and an injector test light, while cranking. If you have neither spark, nor injector fire, you may have a faulty crank sensor, or ECM. On the earlier models, a bad injector(s) can cause the driver in the ECM to shut down due to over-current. This usually is accompanied by a stall condition, and subsequent no start.