I recently bought a 89 F 250 and that system has been messed with,the divertor valves must have went bad and replaced with pipes and the pipe going to the cat is gone. Truck has a serious hesitation problem when cold and still does not seem like it has full power when warm and it got me thinking it could be the way the pump system is now hooked up,with the air going to heads and exhaust manifolds at the same time could it affect the oxygen sensor making it not run right. If the pipe going to the cat was still there I would direct the air there but now thinking about getting a shorter belt and not having the pump working.

 

Disconnecting the the air pump solved the hesitation problem,too much air going in before the O2 sensor.