Ford Repair: Poor running engine and an engine warning light that goes on and off, ford conversion van, warning light

Question
I have a 1993 ford conversion van equipped with a 302 engine with an auto trans. It has 83000 miles on it. The engine runs rich and gas can be smelt by the exhaust pipe.It runs rough. I have taken it to my mechanic who has told me that since the "check engine" light does not stay on all of the time the codes cannot be read! I just had an exhaust manifold replaced and the plugs replaced. I still have the problems. Any help will be appreciated.

Answer
Hello and thanks for the question...I'll try to help.
Even though the check engine light isn't on all of the time....when it does come on fault codes are stored. Have your mechanic check the computer system and go from there.
Hope this helps,
Erik