For the fuel injected cars, I have found Redline fuel injector cleaner works well.

I use STP oil treatment regularly in my 82. She burns and leaks oil, so to help prolong the life before the eventual rebuild....

I add 2 stroke oil to the diesel in the 2000 Powerstroke. Helps lubricate the injectors. When I don't use it the injectors clatter.

I Seafoamed a Jeep Cherokee and the smoke from the exhaust was enough to bug fog the entire neighborhood. Jeep ran better after....

Never tried MMO, but have put ATF in the engine oil to clean a motor out.