Will a 1994 Dodge truck engine 5.9 Cummins twelve valve fit in 2003 dually?

While both are Cummins 5.9L 12-valve engines, a direct swap from a 1994 Dodge truck into a 2003 Dodge dually is not a simple bolt-in affair. There will be significant compatibility issues. Here's why:

* Engine Mounts: The engine mounts are different. You'll need to fabricate or find custom mounts.

* Wiring Harness: The wiring harnesses are completely different. You'll need a custom harness or extensive rewiring. This is a major undertaking.

* Transmission: While both trucks likely used automatic transmissions, the specific transmission, bellhousing, and adapter plate may not be compatible. You may need a different transmission or adapter.

* Electronics: The 2003 truck's PCM (Powertrain Control Module) is likely incompatible with the older engine. You'll need significant adaptation or potentially a stand-alone engine management system.

* Exhaust System: The exhaust system will likely need modification or replacement.

* Accessories: The location and type of accessories (alternator, power steering pump, etc.) might differ, requiring modification or replacement.

In short, it's a major engine swap requiring significant fabrication, electrical expertise, and potentially a substantial parts budget. It's not a project for a novice mechanic. It's far more feasible to rebuild or replace the engine already in the 2003 truck than to do this swap.