will a 93 ford explorer engine work in a 99 ford explorer ???

This post assumes both engines are 4.0's. The 93 was a member of the first generation. The 4.0 engine went through at least six (I know of) revisions up to 1999. Even if the engines swap out you will have PCM issues which will have to be addressed. Besides, if any mechanic has to do engine work in the future, you will have to tell him which engine is currently in the 99 so like internals can be purchased, mane parts are not interchangeable. Ford offers a crate engine for the 99 4.0 OHV engine for 2600 bucks, minus installation. The crate engines comes with intake, water pump, engine oil and spark plugs all installed in the crate engine. You'll have to install new injectors at about forty bucks a piece (motorcraft).