Welcome to the forum!
There are hundreds, if not more, reasons the check engine light (CEL) could come on. You'll need to pull the diagnostic codes and post the specific code(s) here to get many reasonable suggestions to solve this issue.
Your Explorer is right on the borderline for the transition to OBD-II. Pretty much any parts store is able to read OBD-II codes for you at no charge. Some will also be willing to pull the EEC codes for you as well, but if not, you can do that on your own with a jumper wire or voltmeter.
The steps to pull pre-OBD-II codes can be found at the bottom of
this page along with the available codes.
-Rod