Misfire And Not Sure What To Try Next?
 

Out of nowhere my 04 4.6l V8 has started misfiring sporadically with a very violent rough idle. This only seems to happen whilst 'coasting' around a corner, at idle / stopped at lights, or after I reverse up my drive (slight gradient).

I can get around 50 misfire counts in a matter of seconds and only on cylinder #5. Some days I'll drive for 20 minutes and get 300 misfires, other days that can be as much as 1500 misfires. All other cylinders seem to be fine.

I have had a rich code triggered on bank 2 at -37.5% fuel trim. I can smell gas when it starts to idle rough.

So far, I have tried the following:

- Swapped all injectors between banks (injectors were new motorcraft around 10k miles ago).
- Swapped coils from cylinder #5 to #1.
- Installed new plugs.
- Compression and idle cylinder balance is pretty even and fuel trims are perfect (according to my mechanic).

Neither me nor my mechanic knows where to go next with this and I feel that my cats are getting a beating from this... Any suggestions?

Have you checked the condition of your FPDM?

No I have not, but why would this cause a misfire on 1 cylinder only at idle or low revs and high engine load?

What about the COP and or boot and spring ?

He swapped cops between 5 and 1.....My guess is after swapping injectors and cops, that there is a chaffed wire going to cylinder 1.

I have looked at the wires but can't see anything too obvious. Anywhere specific to look?

Usually it will be where the wires enter the COP plug.