1998 ford expedition 4.6 litre?

[bill]

can a faulty gas cap or catalytic conv. cause check engine light to come on?
can faulty gas cap cause check engine light to come on?
can faulty gas cap cause check engine light to come on?

 

[Charles]

and also number 3 coil over plug goes bad on that year.have the parts store check the codes..

 

[Frank]

both of these things as well as many other things can cause the check engine light to come on...if you post what the codes are, i can tell you what system those codes relate to.