1994 Ranger xtra cab
4x4
v6 4.0
5-speed
113K miles

Just bought this truck. When I test drove it no "check engine" light came on, but after purchase driving home is came on and then off many times. It only comes on at high rpm/speed. I have my trusty ODBII scanner but realize that this 1994 was pre-ODBII.

How can I figure out what the CEL is about?

 

do search here and look for the topic on checking the codes. You need a flasher/light and to count the number of flashes then read the code numbers off. Forget who posted but its been many years. I know the plug is down by the emerg brake but thats about it. I dont know where you are at but I had the last ones in cold weather. If this is it it might be a bad tstat. Block off the rad with a piece of paper/cardboard if its cold weather related and see what happens. Mine was on the interstate and going up hill where it was colder.

 

You'd be throwing away ~$20, but if you are scared of the test light/paper clip method, there are still OBD 1 testers on the market. Do a quick Google search and they are still available. Just make sure you get one specifically for Ford, as the Chevy model won't connect.

 

I second Kruse.