Will a 3.8 liter engine out of 1992 Pontiac Bonneville fit into 1996 Bonneville?

It's highly likely, but not guaranteed, that a 3.8L engine from a 1992 Pontiac Bonneville will fit into a 1996 Pontiac Bonneville. Both cars used the same generation of 3.8L V6, so the engine block itself should be largely compatible.

However, there are crucial things to consider:

* Specific Engine Code: Even within the same displacement, there were variations in the 3.8L engine over the years. Different engine codes signify different internal components and potentially different mounting points or accessories. You *must* verify the engine code from the 1992 engine and compare it to the engine code in the 1996 Bonneville. Slight differences could cause compatibility issues.

* Accessories: The placement and type of accessories (alternator, power steering pump, A/C compressor, etc.) might differ slightly between the two years. You may need to adapt or swap some accessories to make it work.

* Wiring Harness and Computer: The wiring harness and the engine control module (ECM) are not interchangeable. You will absolutely need the wiring harness and ECM from the 1992 car, or possibly have a custom harness made.

* Exhaust System: The exhaust manifolds and possibly the catalytic converter might not be directly compatible.

* Mounts: While the engine block might fit, the engine mounts themselves may require attention.

In short: While the basic engine block is likely compatible, a direct swap isn't a guaranteed plug-and-play affair. You'll need to carefully compare the specific engine codes and anticipate needing to adapt various components, including the wiring harness, computer, and possibly exhaust and mounts. A mechanic with experience in such swaps would be invaluable.