OK guys this is what i have found with the 91 ford f150 i have. i looked up the casting numbers and found out the kid i got the truck from replace the engine with a 5.0L engine from a 1987 f150 and now i am finding that the engine will not work with the 1991 pcm and some one told me that i should get a pcm from the junk yard for the 1987 motor and see if that would work. has anyone ever ran across anything like this before? if so did you find a fix?

 

The engine should work. The pcm should work, all mtors from 85-94 use speed density, the only thing is maybe some sensors are different. Give it a try. The basic engine from the manifold down didnt change much.

 

At some point in '93 they went to roller cams with a different firing order. But yes I agree with dirtcrew51m. The motor should work just fine. At one point I had a '87 motor in my '93. I just had to change the cam to match the '93 firing order.