2003 Expedition 4.6 Rough idle/Miss/Blowing Fuses
 

Hey guys.. New to the forum... Have a couple of questions...
I have a 2003 Expedition with the 4.6Liter V-8.... 157,000 miles...
It has been running SUPER rough lately.. The check engine light came on so I brought it to Auto Zone to have the codes read... Well they couldnt get the port to show power so they told me to check the fuse.. I did, it was blown.. I replaced the fuse and they read that there is a Cylinder 7 misfire...
I JUST replaced the plugs and boots on the coils about 5 months back.. so I purchase a coilpack.. The old coil pack shows the same resistance as the new one.. So I put the old one back on and bring it back to Auto Zone for another read... Fuse is blown AGAIN.. Replace it and they read it again.... Same thing, I asked the guy if the old coil pack is showing the same resistance as the new one if it could still be bad.. He said that yes, that there are two ways of checking a coil.. if the resistance shows fine then they can "stress test" the coil... He suggested I go ahead and replace the coil... I bring it home and put the new coil on.. On acceleration it IS running better, but still has a smaller miss, and during the idle it idles ROUGH!!! Didnt idle this rough before the coil was replaced... Could the bad coil have done something to the spark plug??? Fouled it out?? I removed it and it looks dry, not a lot of black carbon, but it has what looks like a red or rust colored dry cover over the whole surface of the plug... ???
What could be the reason for the miss, and why would the fuse for the port keep blowing?? Does that fuse operate anything other than the port that you plug the scanner into???

Thanks guys...

wes032,

I wish I could hlep you. I've had to have all 8 coilpack replaced on my 2003 expedition one at a time over the past 14 months. I did not have any problems with fuses which leads me to a question... Where exactly is the fuse panel on this vehicle? I blew a fuse this weekend trying to replace the radio and I haven't been able to locate the fuse box?

Thanks...

DelKoman

If I remember correctly, which is not too often, there is a fuse panel under the hood on the driver's side and also one inside the vehicle under the driver's side instrument panel.
Owner's manual should tell which fuse controls what.

I had a similar problem with my 2002 Navigator equiped with a 5.4L 32 valve engine. The car started to idle rough, so I took the car to my mechanic. The computer code poited to the #8 coil pack and he recomended to be replaced. After the coil pack was replaced the engine was still running the same. So I took the car back to him and he did a compression test and found out that the #8 cyclinder did not have as much compression as the rest. So it turned out to be a burnet valve.

You have my curiosity going now, was there any explanation as to why the valve was burned and only one?

I suspect that thes reason the valve went bad was due to not using the specified octane fuel in the vehicle. The owner's manual called for a 91 octane gasoline and I used the lower octane ones. Also, I used the vehicle for towing a boat to Colorado river for 600 miles of round trip several times a year with tempratures over 115 degree. Even though, the car never overteated. As far as why only one cyclinder was affected, not all valves go bad at the same time. Since the cost for valve job for this engine was $3,500, I unloaded my Navigator before the rest of the valves went bad.

Again, you should have your cyclinder's compression check, it's a simple process and it might point out the problem.