Engine Mechanical problem
2003 Ford Expedition V8 Two Wheel Drive Automatic 121000 miles
I've replaced spark plugs, and brought to the shop several times. There weren't any codes for a while to be pulled, but when it finally did, it showed misfire on cylinder 5 (which is one of the ones I replaced). We replaced the coil and plug but still runs terrible. I have no idea where to look next. My mechanic suggested it may be the Catalytic converter, but he doesn't look into those types of issues. I don't want to spend another $100 just getting Ford to look at it. If you have any ideas what some possibilities could be, it would be greatly appreciated.
Check and test the following below: Oxygen Sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)
Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include: Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
Cap and Rotor