I had this similar problem with my 97 F-150 4.6 L, it ended up being a plug that was going bad. The SES light never came on, finally after it did they were able to diagnose the problem.

 

COPs is your answer. I went through all of the same issues, changed this and that, cleaned this and that, over thought many of my symptoms trying to avoid the cops and plugs. Finally changed them out and it runs great now. You can pick them up on ebay for about $20 a piece versus 90 at Ford.

 

I am sure you can check the COP's via resistance, but being that this problem was intermittent I opted for the trial and error method. I broke down and bought one COP. I installed it on the #1 cylinder then took a test ride. This didn't fix the problem. Replaced the #2 COP with the original #1, again did not fix the problem. Did the same thing for #3. Due to accessibility, I jumped over to #6 and bam, the hesitation went away. I could not believe it only took four tries. I drove into work today without the aggravation of surging, bucking etc. Now that the truck runs 99.9% better but I can feel a slight skipping at idle and it seems that I do not have 100% power on top end. Could be my imagination.

Is it common to replace all of the COP's when one goes bad?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>

 

Common? Yes, when a mechanic talks you into it because they are making money on each COP

Buy another one, and round-robin it again.

 

You've probably heard this diagnosis before, but I don't see it here. I had a miss under a load (showed up as engine warmed) for the last two years. If you search under 'miss under load' my post comes up near yours. I have a 99 F250 with the 5.4 and had a plug blew out at 109,000 miles. I had to have the head heli-coiled, and when I did I had Autolite plugs installed.

Well, I moved to Colorado and a few months after being there it started this miss under a load thing. Check engine light came on, and Auto Zone showed it was a bad EGR valve. Replaced it, no change. In fact, I still get a code from that, but that's another story. Well, two weeks ago I decided I'd had enough of the miss and since it was getting worse was afraid it was about to leave me stranded somewhere. I went to the dealership and bought 8 new Motorcraft plugs. In the process of installing them, I found all of the COP boots in good shape with the exception of the #7 boot. It was cracked at the top.... bad. In fact, the guy who did the work I mentioned earlier had apparently siliconed it instead of replacing it. I guess when I got to the dry-cold climate of CO it was too much, and the silicone separated from the boot, and the arching began....and has persisted 'til now. I changed the plugs, but they weren't the culprit, it was a bad boot. Put on a new one, 15.00 bucks form Advance.....MISS GONE.

Sorry so long, but it's a good chance this is your issue to.

 

Issue was resolved - bad COP on #6 cyl. Truck runs great, however the Check Engine Light decided to come back on. Auto Zone says its is poor EGR flow.