Ok, so guys, I too am experiencing the same herky jerky motion about 45 mph, but...I can also feel a misfire. A definite miss when I put the engine under a load, if i gently put a load on, herky jerky, if I bury the pedal miss fire. I was totally convinced that it was ignition. So I pulled every coil, every plug, and of course it was not until the very last plug I found a boot with a hole burned through it. I was so satisfied that I found the smoking gun, but that wasn't it! This thing still jerks around and misfires and does not throw a code, if anything its worse. I have tried so many combinations to make it throw a code and it wont do it. I have ran the scanner in the pending mode, nothing. I hate the idea of pulling each COP one at a time to eliminate the problem, most likely because I don't think I will find the problem like that. I have read vacuum leaks? weak coils, a positive charge in the freakin anti freeze? I just don't know that to do next. Thanks for letting me rant.
Now it's time to listen.
You have at least one low output coil.
Again, here is the reason you have the miss.
At speeds between 45 and 60, the EGR system opens and causes a very lean air to fuel ratio.
This come about because the program that calls the EGR into operation causes a very lean fuel to air mixture by commanding the fuel injection to cut back as well as advance the ignition timing in addition to the exhaust being gated into the intake making the mix leaner yet. Exhaust gas does not burn the second time..
The results of this "normal" condition is a rise in coil voltage requirement because.the mix is in the 20 to 1 range and must have higher coil reserve voltage to fire the mix. A failure to fire is a missfire at that time.
This situation is not a "hard fault" so does not set a code because it is cancelled in memory as soon as the operating conditions change.
So, the next time this happens you get the same result over again;
it is a proven fact.
If you do not approch the fault in the proper way, have fun and enjoy the missfires.
Replace the offending coil or have them tested for output to find the one causing the hassle.
You may see this stored in another part of the program then again you may not.
It takes a good scanner not a reader to see anything and to "TRAP" the fault while running when it happens.
Exact same symptoms as my 98 had. Had a bad plug wire. Agreed, you will find a bad/weak coil. It emulates trans shudder when it first starts going bad but, in my case anyway, it deteriorated rapidly to way worse than shudder could ever be.
Bluegrass, thanks for the info. I am listening and you make total sense. A couple of weeks ago I pulled all the COP's and plugs. When I read the plugs I saw a very lean running engine. It surprised me. So again, what you are saying makes total sense to me. I have a mix of OEM and aftermarket COP's There is 130k+ on the OEM's. I dont know that would make a difference because many say to stay away from the aftermarkets. So I ask, does that hold true for some of the performance aftermarket COP's, say like the MSD's. I think someone earlier in this thread or maybe another said to replace the entire set! I freaked because thats like $750 worth of coils from the dealer. I found a pretty good deal on ebay for an MSD set. Thats why Im asking. For $300 and free shipping I would spend that much at the dealer for them to TS and replace one COP. Then like some other guy said, another coil fails two weeks later. Hey, thanks for your help.
Yea!!! Bluegrass! I replaced the COP's, new o-rings on the injectors and all is good. I did not replace the plugs because I installed Motorcraft Platinum plugs less than 30k ago and they looked fine.