I was wondering what is the difference is between the 4.0s. I know the 87-88 had 150HP the 89-90 had 175HP and the 91+ had 190, whats the reason for the increase? Was it internal engine or something with the fuel injection? I know the 91+ fuel injection is suppose tp be better, but why? How is it different from the older style? Just wondering so that i can plan what i need to do when i rebuild or change out my engine.