[who fan]

I Dont know what the hell interior pumps are. But my 93 F150 ran rich turned the plugs black I changed the coolant temperature senser for 20.00 dollars at Advaced auto parts fixed my problem. This senser is right next to the thermostat. you will need to drain aproximently 1 gallon from your radiator. PS mine is the 302 so your may be different. I do know one thing most mechcanics have become relaint on check engine lights because thay are trained that way. No check engine light = bad ECM, NOT SO!