My Expo 4.6l has 100,000 miles like any good vehicle owner I changed the plugs
in it. First, I used bosch with I throught started the problem. Then, I was told to change them to motorcrafts and that would cure the problem. Change them out today and still the same problem a missfire under a load at about 2000rpms.
I have been probing the site for answers the most interesting thing that I have found about a solution. That people having problems like this telling them to use dielectric grease when installing the plugs. Now could this really be the problem.
Maybe something else, just seeing if some one has had I simular problem.

 

While the engine is running remove each fuel injector electrical connector plug-in one at a time when you remove one that does not cause the engine idle to drop off, then you have found where the problem is, most likely a bad wire or COP could even be that you cracked a plug while installing. (Not likely since it happens with two sets of plugs) You can also watch the tachometer and if it does not drop off when an injector connector is removed you have narrowed it down. Dielectric grease is not the cause of your missfires

 

Do you have a missfire code?
If not how do you assess there's a misfire?
When is the missfire, full time, just under load etc.

 

Good luck and welcome to the Forum.

Are you sure the boots are on the plugs good? I've had 1 back off on me twice (don't have COP) when I changed the plugs and wires.

If it ran fine before changing plugs, I don't think something else failed but then, it could be a coincidence.

 

With the bosch plugs I did get PO401 insufficient EGR flow the motorcrafts no codes as of yet. I just wonder if I damaged an injector pulling them out. It dose miss under a load between 2000 and 3000 RPMS higher than that it seams to clear up.

 

I think you have EGR problems. That will make the engine run rough but is not really a missing condition.