The 5.4 Litre Engines = Nightmares in some situations. I had the identical power plant in my 2006 F150 . I would say there is very little chance that your misfire is coming from bad piston rings. Your engine has 8 separate coil packs---one for each cylinder. I will bet one of those coils are bad causing a misfire...and it may be an intermittent thing too. Are you getting a check engine light? if so, take it to Auto Zone and get a reading. Often, a reading can pin point exactly which cylinder is misfiring.
Now, this engine is famous for spark plug issues as well. The factory two piece spark plugs are famous for breaking off in the cylinder head during the removal process (In fact, there is a Ford Service bulletin addressing this exact issue) If by chance you are considering changing the plugs, follow the service bulletin EXACTLY before attempting to remove the plugs. Make sure you have read numerous articles and watched the available YouTube videos on this exact situation. It can be a nightmare if the plugs break off. In fact, I off broke 6 of 8 plugs when I attempted mine. If you are unlucky enough to break off the #4 or #7 or #8 cylinder plugs, these are a real issue to remove.
I visited a local Ford dealer to ask for help or suggestions on this issue. The service manager took me in the work bay area and showed me an Expedition with the entire body removed from the chassis. The removal was required to gain access to the cylinder heads because of the broken spark plugs still inside. He told me this was a $4000 job.
Get a second opinion....maybe a third. You make get lucky
Now, this engine is famous for spark plug issues as well. The factory two piece spark plugs are famous for breaking off in the cylinder head during the removal process (In fact, there is a Ford Service bulletin addressing this exact issue) If by chance you are considering changing the plugs, follow the service bulletin EXACTLY before attempting to remove the plugs. Make sure you have read numerous articles and watched the available YouTube videos on this exact situation. It can be a nightmare if the plugs break off. In fact, I off broke 6 of 8 plugs when I attempted mine. If you are unlucky enough to break off the #4 or #7 or #8 cylinder plugs, these are a real issue to remove.
I visited a local Ford dealer to ask for help or suggestions on this issue. The service manager took me in the work bay area and showed me an Expedition with the entire body removed from the chassis. The removal was required to gain access to the cylinder heads because of the broken spark plugs still inside. He told me this was a $4000 job.
Get a second opinion....maybe a third. You make get lucky