1991 Ford Explorer Help Replaced fuel injectors and still n

I bought this ford explorer from my former boss and he said it ran when he parked it, the only issue he said was his nephew took out the PCM to put in his truck (don't know what kind) and he said it was a two wheel drive. When I first looked at the truck and tried to get it running it had no spark and I had to change the crank sensor to get fire from the coil pack. All I checked at the time was the fuel going to the fuel rail so I thought it was fine as far as the injectors were concerned. Well my mechanic friend told me that the injectors were probably bad so we took it apart and check them (injectors) and he said that they needed to be changed. Well I bought all new injectors and even took the coil pack and crank sensor off of a running vehicle and installed everything and now I only get spark every now then and I still don't think the fuel is going past the fuel rail or injectors. What do you think I should do about my problem? Is there a way to see if the wiring harness that goes to the coil pack and the injectors are good? What do you think I should do? Also it has the 4.0 motor.