Expedition & Navigator1997 - 2002 and 2003 - 2006 Ford Expedition and Lincoln Navigator
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Nice, most likely it is the coil. I had the same problem but cylinder #4. Your lucky cause it's #3. That one is the passenger side of the motor; third plug back. Take the 7mm bolt off and pull the coil/boot assembly out and replace. You might get away with just replacing the boot, but I doubt it. Have fun
Remember on some models the heater hose to heater tube is directly over the #4 coil. The hose clamp from the factory was not properly tightened and seeps antifreeze on the #4 coil assy, and kills it. This was a big problem. Replace the clamp, dont try to tighten it.
I moved coil from cyl3 to cyl1 and moved the problem! now P0301.
FYI: Standard Motor Products now makes a repacement boot part number SPP39, Advance Auto Parts has a listing online but no instore stock. For now I will spend the $50 on a coil, research is just the boot bad later.
My son replaced the plugs and wires about 8,000 miles ago, with no problems at all during that time. Then about 1,000 miles ago, the "check engine" light came on and stayed on. I rechecked the wires and checked for vacuum leaks, and found nothing wrong. AutoZone ran the codes and we first got a code P0300, which is a "random multiple misfire". Not much to go on. They reset the computer and a couple weeks later the "check engine" light came on again. A code P0303, "plug 3 misfire" popped out of the computer. I checked plug 3 and found nothing wrong. The weird thing is that this afternoon the "check engine" light went out, and has not come on again after about 50 miles of driving.
My son-in-law, a Ford mechanic, had previously told me to run some injector cleaner through the engine because he thought the number 3 injector was clogged. Turned out he was right. I ran Lucas injector cleaner through three tanks of gas and the "check engine" light mysteriously went out this afternoon. This may be of help to you if your "check engine" light comes on again and you get a code P0303.
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