I have a 1991 sho 3.0 MXT I did a motor swap and put a 89 3.0 sho in it. I had to change the motor wiring harnnes for it to run. When you try to crank it it will backfire a couple times then crank right up and no skip. Under alot of power (4500-6500) rpms it will start to backfire and cut out...