Will a 1994 Ford F-150 5 liter engine fit in 1990 F-150?

While both are Ford F-150s and use similar architecture, a direct swap of a 1994 5.0L (302 cubic inch) engine into a 1990 F-150 isn't a simple bolt-in affair. There will be compatibility issues. While the engine itself *might* physically fit, you'll encounter problems with:

* Engine Mounts: The mounting points might be slightly different, requiring modification or custom mounts.

* Wiring Harness: The 1994 harness will be different and incompatible with the 1990 system. You'll need to either rewire extensively or find a harness from a similar year 1990s 5.0L truck.

* Computer (ECU): The 1994 engine's computer is specific to its year and will not work with the 1990 truck's wiring and sensors. This requires significant modification or swapping to a compatible computer.

* Emissions: Depending on your location, emissions regulations might make this swap difficult or impossible to pass inspection.

In short, it's *possible* with significant mechanical and electrical knowledge and fabrication skills, but it's not a straightforward swap. It's a project that requires considerable time and effort. You'd be better off finding a 1990s 5.0L engine and related parts to keep compatibility simpler.