I have an 89 F250 It had a 302 in it, and I had it made into a 347 stroker, and put a larger cam in it that is suppose to work with the computer. We can get it to start right up and it runs great when its cold, but when it warms up it runs pretty rough. The guy helping me with it says when it goes into closed loop is when it starts to run rough. It will back fire through the intake if you rev it up fast also when its warm. Any ideas, thanks

 

Camshaft specifications? If you did not stay near a 114 degree LSA then you will have problems using the factory tune with a Speed Density system. Even with a tune going much under that number can be difficult to deal with.