I have a 93 XJ-S with a 4.0 that I bought non running two years ago. It had no compression on two cylinders so I replaced it with a used engine. For what ever reason I don't have spray from my injectors. If I jump power and ground direct to the injector it will spray. I have good 12v power on the pink and blue wire. I have a ground signal on the pink and black but it is faint, obviously not strong enough to let the injector fire.
Good spark, and weak signal on the injector, tested with noid light and test light, so having a signal would lead me to believe that the crank sensor is good. I also have a spare motor for the car and have changed crank sensors with the same results. Car will start on ether.
Am I correct in thinking that it is a computer problem, other than the two years i have owned it, i know very little of the car history. Supposedly the guy that had it before said that it had gotten hot so he parked it.

 

I had a no start with no power to the injectors
It turned out to be a faulty relay in the passenger side front fuse box. The relay has a blue base and I believe is called the engine control module relay.
It might be worth a try checking to see if this relay is good.

 

I have power, and ground actually, but the ground signal is weak. While removing the injectors earlier I actually bent the fuel rail, which wasn't an issue since i have a spare sitting here. So I put the other fuel rail and injectors in and it started... Wtf! They are both green stripe injectors, and the same plugs, so I wouldn't think that would make any difference. They other thing I did was put the charger on 200 amp boost. I have read these cars can be sensitive to battery voltage but I have had it on that setting before.

Maybe all I needed to do was post on here!