* Engine Management: The 1996 318 uses electronic fuel injection and a sophisticated engine control module (ECM). The 1986 D150 likely has a much simpler carburetor-based system. The wiring harnesses, sensors, and ECM are completely incompatible.
* Transmission: The transmissions are different. You'd need to swap the transmission as well, and even then, compatibility is not guaranteed without significant modifications.
* Mounting: The engine mounts and accessories (alternator, power steering pump, etc.) are different. You'd need custom motor mounts and potentially significant fabrication.
* Exhaust System: The exhaust system is completely different and would need to be replaced.
* Wiring Harness: As mentioned, the wiring harness is completely different and would require extensive rewiring.
While technically *possible* with a massive amount of custom fabrication and engineering expertise, it's not a practical swap. The cost and effort involved would far outweigh the value of the result. It would be much simpler and cheaper to find a suitable engine for the 1986 D150, or rebuild its existing engine.
