I changed the eng on this Jeep, and it ran fine but knocked. I took it back out and replaced a bad piston. Then it would not fire. I T/S down to when the fuel pump relay is out it fires fine. I tried jumpering the fuel pump from the batt and as soon as 12v is put on the output side of the fuel pump relay, firing stops. (from coil lead). This is the same with the fuel pump disconnected at the tank. The diagram shows this output going to the A/C sys but is not specific. I have tried disconnecting the A/C and turning it off.

Help?