I have a 2000 E-150 with a 4.6 with coil on plug ignition. There is a bad stumble / misfire when accelerating. The problem is most noticeable when the throttle is slightly open as when driving in city traffic. If the engine downshifts the stumble is gone or at least much less noticeable. There is never a check engine light.
I took it into one of the major tune-up chains in my area and they diagnosed the problem to be a bad fuel pump because they are seeing that the fuel pressure is low (35 PSI) and drops off to almost 0 when the engine stumbles.
This van has only 36,500 miles on it and drives fine except for the miss under acceleration. The van has a new fuel filter and I have always kept the tank above 1/4 tank since I bought it new, so I am skeptical that the fuel pump is bad already.
My question is - if I had a bad spark plug or coil causing the misfire, would the ECM toggle the fuel pump to eliminate damage to the catalytic converter?