04 F150 4.6l had check engine light and misfiring coil. Changed battery. Code gone. Misfire still there but no code??? Do I just have to buy and swap all 8 coilpacks?

 

The fault codes and check engine light for misfires only occur when the misfire rate exceeds a calibrated threshold. If the misfires are not severe enough for that, you have to use a scan tool or equivalent to look at the Mode $06 misfire per cylinder to see which is having the current issue. Otherwise, you're left with loading up the parts cannon and hoping you get lucky.

Disconnecting the battery resets the PCM and clears codes until the next time.

 

If it's like my 02 5.4L, it has to misfire for a while before it sets a code.

 

As I said, "The fault codes and check engine light for misfires only occur when the misfire rate exceeds a calibrated threshold.".

 

I just went through this on my 02 and it misfired a heck of a lot before it met the "calibrated threshold". I was afraid I was going to melt the cats before it finally threw a code to let me know which cylinder was misfiring. I had two cylinders do this over a few hundred miles. Sooo, I replaced all of the plugs and cops using Motorcraft cops from rockauto.
By the way, I really appreciate your knowledge and participation in the forum! "Thumbs Up"