I have a 2006 5.4L F150.

I am encountering a misfire on the #3 plug.

I have checked the plug, and it looks pretty good.

I have recently changed all COPs.

I have removed the wire connector from COPs and checked the voltage while the vehicle is running.

The #3 connector is measuring around 13.6V

The #1 and #2 voltage at COP connectors is 0.17V.

While the voltage at #5 and #8 COP connectors is around 0.4V.

I brought it in to a mechanic and he indicated the computer needs to be replaced, no signal was getting to COP.

Any ideas a to what the problem is?

thanks,

 

So, what appears to be happening is the ground wire going to the #3 COP is not opening and closing, and just staying in closed, hence why I get the 13.6V. The other signal wires from computer are working properly, since the low voltage reading. I still need to verify this with led tester.

I also know this is the same thing at connector as well as right near the ECU.

So, if the computer is keeping this neg signal wire closed all the time, does this mean the computer is surely faulty, or could it still be something else keeping this #3 COP signal wire closed?

Is it the cam that makes this negative signal wire open and close?

 

I have hence gotten a LED test light and verified the other COP connector wires cause the test light to flash, while the #3 COP wire connection to just stay on all the time, mo blink signal.

The only OBD error messages I receive are from misfire on #3, no other faults.

The engine sounds pretty good, maybe a slight tick sound. But the misfire wobble is apparent.

I figure I will change the computer at this point, since it appears this is where the issue is.

What else could interfere with the COP neg signal?