My check engine light comes on every time my fuel level gets down to approx half a tank. It stays on until I fill the gas tank full again. this only happens to the truck in the warmth of the summer. come winter there are no check engine lights at all. Got misfire on Cyl #2 diagnosed so we changed the coil over to another cyl and there was no problem( I guess because of the reset of the computer). Someone mentioned that this could have something to do with EGR. But, thats beyond my scope of knowledge. Any opinions would be great.

2003 F150, 4.6 100k

 

I'm confused, was the warm weather CEL a misfire on #2 or something else?

 

Sorry for the lack of clarity. Yes, the CEL only lights up in warmer weather.

 

I think I remember this happening to people who needed a new gas cap, because the old one wasn't venting properly.