I need a new engine for a 91 Trooper MT. The junkyard search engines say that a 2.6 from a 94 Rodeo is incompatible and a 97 truck engine is also incompatible, not only with the 91 but also the 94. What makes these engines different from each other? Is it because of OBDII? What would I need to do to get a newer engine to work?