Will late model 08 f150 4.2l v6 work in a 99 4x4 with original engine?

No, a 2008 4.2L V6 from an F-150 will not directly work as a replacement for the original engine in a 1999 F-150 4x4. While both are V6s, there are significant differences that make it incompatible:

* Engine Management System: The 2008 engine uses a far more advanced engine control module (ECM) and associated wiring harness than the 1999 truck. The 1999 system simply won't be able to communicate with the 2008 ECM.

* Wiring Harness: The harness connectors are different. A massive amount of rewiring would be needed, making the swap impractical.

* Transmission Compatibility: The transmissions used in those years are not interchangeable without major modifications. Even if you could get the engine running, you'd likely need a different transmission.

* Mounting Points: While the engine bay might seem similar, the exact mounting points and accessories (alternator, power steering pump, etc.) likely differ enough to create serious problems.

In short, the complexity and cost associated with adapting the 2008 engine to the 1999 chassis far exceed the benefits. Finding a used engine of the same year or a compatible model for your 1999 F-150 would be a much more feasible and cost-effective solution.