I think you should buy a basic handheld oscilloscope from amazon and start probing your injector lines off the ECU, if those appear to be fine then prob your fuel pump circuit.
Oscilloscopes are great tools because they are like a multi-meter that plots changes over time, so you can see how...
As stated previously the spark plug tubes are NOT replaceable. The seals are.
I'm never a proponent of firing the parts cannon at a rig unless you are baselining it. True diagnosis takes time to understand how to do and time to actually perform, but the payoff is not spending money on parts...