2000 Duratec misfire

[DjDio]

I have a 2000 SEL with the 3.0 Duratec. The car idles and runs rough. Once in a while on acceleration it runs better and you could feel it kick and it runs good but very rare. I keep getting a code for misfire on cylinder 4. It has coil on plug. When i take the spark plugs out # 4 always has carbon on it. I swapped out the coils from one cylinder to the other that i knew were good and # 4 still misfires. While the car is running if i unplug # 4 coil it makes no difference at all but if i unplug one of the other coils it runs rougher. I also took a good coil and put a plug in it with it not in the motor and plugged it into # 4 and started up the car and it has a very weak spark compared to the other cylinders and i did this in the dark. So far this is what i have done.
1. Replaced spark plugs
2. Replaced coils
3. Replaced both the cam and crankshaft sensors
4. Fuel filter
5. Intake gaskets
6. Air filter
7. PCV and hose
BTW the 2000 Duratec has a coil on each plug with no traditional spark plug wires going to one coil or a coil pack.

[shorod]

Have you checked the primary voltage to the coil for cylinder #4? Since it's triggering I don't suspect it's an issue with the camshaft position sensor.

-Rod

[DjDio]

I was planning on getting a tester tomorrow morning and checking the voltage. I have the wiring diagram for the ignition system and the wire for coil 4 going to the PCM seems to be fine. But lets say the voltage that goes to the coil is low, what would cause that? Could the computer be bad? I don't think it's a compression problem because sometimes driving it does run great. Has all it's power. Although it always misfires at an idle. Like when i compare the spark on the end of the plug with one known good coil #4 is always week. When i rev it steadily at 2500 rpms or so i can see the spark firing intermittingly on the plug. From dim and weak to bright and blue volts.

[shorod]

If you have low primary voltage to the coil for the cylinder I'd suggest you check all connections and, when possible, check for continuity. If you have a loose or dirty connection under load there will be a voltage drop through that loose/dirty connection.

-Rod