The injector wiring is switched by the gas to turn off the injectors stopping the supply of petrol to the engine. From memory there's a wire for each bank that is cut normally at the ECU,if you find these and rejoin the original wiring this will show if the fault lies within the gas systom or it is a petrol problem. Remember to turn the gas system off on the controller if your trying this.
I've seen this problem on a 4 cylinder engine that would run on gas and not petrol, turned out to be a corroded conection on the emulator box. Depending on your system a V8 has 2 emulator boxes, one for each bank, to shut off the injectors.
Best of luck,
Stevie.