gross polluter

There are lots of sensors on a 1993 3.3. I can think of at least nine just off the top of my head. You don't just "replace them" at random. Sounds like your van probably needs diagnosis and repair, but you haven't given enough info for anyone here to help you.

If you replace them all, whether they need it or not, you still might not remedy the problem at hand. It could also need a new catalytic converter, even after you replace sensors that might not ALL need replacing.

As mentioned, get a tech to use a CHRYSLER scanner (not an aftermarket version as such) to pull the codes and see what's going on. If something's that bad, it should have the "Check Engine" light blazing--unless somebody took it out.

Don't rely on what an auto supply says their scanner says your vehicle needs either. Some sensors might show "bad" when the code they are supposed to have can be caused by another sensor not being good. Fix the original one and the other codes might disappear. Just as in the "old days", some things can interact to cause issues that make some good things operate badly, so you need to know how these things relate to each other.

Or, you can continue as desired and spend your money on your vehicle and still not get it completely fixed. The dealership diag fees might sound high, but it can be less expensive than the total cost of a bunch of sensors that you didn't really need to replace.

Just some thoughts,

C-BODY