I'm going through this truck problem by problem. Picked it up a month or 2 ago. Since then, I replaced the leaking exhaust manifolds and egr system, thanks to other threads I posted and the great help I got from all you out there.
The truck is a 1997 F250 light duty extended cab with the 4.6 triton v8.
The motor appears to run smooth and idles good, from my perspective. It accelerates smoothly, as well, and seems to cruise at an otherwise smooth rate. Until I hit around 50. Then it transitions right into a shake, or vibration. I know I need to be more specifc with the symptoms here, but it's pretty hard to feel where it's coming from. I feel it in the steering wheel, but also, it feels like the whole truck. My dog, oddly enough, will look at the center floor with his head tilted, when it starts to vibrate, as if he's saying, " What the hell is that?" lol. I know he's got a better sense of hearing then me.
So, up to about 60 and over that it seems to go away. Sink back down below 60, vibration is back. below 50, seems to go away. It does it in and out of overdrive, does it when I pop it into neutral, but when truck speed goes down below 50 or over 60 for the most part, under various said stimuli, the vibration fades away. I'll also add that the vibration increases substantially with greater acceleration...The more gas I give it, the worse it seems to get, but still, only within the 50 to 60 range. Not as bad when cruising and/or coasting, but still vibrates regardless. Otherwise, acceleration from dead stop and over 60 is good.
So far, I rotated the tires and only difference I noticed after this was a little bit of a shimmy at 40 to about 43 mph that wasn't there before I rotated the tires. They probably need to be balanced, but the vibration at 50 to 60 doesnt seem to be tire related. The 50 to 60 mph thing is more like an overall vibration. I'm thinking driveshaft maybe? I checked the u-joints and they seem pretty tight...no movement I could feel by hand. I also check the front end a little bit, and tried to see if anything looked or felt funny, like any excessive play in the ball joints or tie rods, etc. That all appeared okay. So, for now, I just try to avoid 50 to 60 mph. Harder then one would think...you end up either getting tailed or tailing someone. I guess that's all for now. If you need more info, I'll try to get it to this post as soon as I get a chance. Also, not sure of the trans I have. You all probably know better then me, but once I get a chance to check, will let you know. I don't think it's trans related or torque converter. Im not slipping or knocking, but forgot to check the trans fluid, which I will also update the condition of that when I get a chance. Also, engine seems to run smooth. I didn't change out the plugs or wires per what I would think normal maintenance, but have nightmares of doing the plugs and breaking one. especially on these tritons. I had a e350 with the 5.4? that blew a plug and stripped out the threads. pain in the...
this 4.6 doesnt look any friendlier to navigate, with the fuel rails in the way and all. But if that is the problem and needs to be done, well, I'll get it done if I have to. But, like I said, idles well and accelerates up to 50 fine...no ticking or unusual sounds, at least that I notice.

 

sounds like you checked the right places but here goes....
U-joints, remove the driveshaft and "feel" the u-joints there should not be any binding. if you feel any binding, replace them. Have all 4 tires balanced, by the way what kind/size tires do you have? How many miles on your truck?

 

You have a misfire in that driving range.
Faulty coil, or plug wire.
.
Why: In that driving range the EGR opens.
This operation causes a very lean mixture.
One of the coils cannot supply a high enough voltage to fire the lean mixture.
.
How to find it; use a Scanner able to look at live data and call up mode 6, test 53.
This will show you the misfire monitor for each cylinder.
The one with the high count, out of limits is the misfiring cylinder.
It will not set a code because it's not a hard fault but comes and goes with driving conditions.
Good luck.

 

Sorry, should have put that info in the first post…the tires are Uniroyal lorados 245 75r16. The truck is a 97 and has about 152,000 miles on it. I also forgot to mention it is a 4x4. I definitely wanna replace the tires, so was holding off on doing anything to these (I.e. balancing), rather put the money into new tires.. Now, I don’t have an accurate history of the truck. I do know it sat for quite a long time with very little use. here and there. Aside from that, not sure of how it was serviced and taken care of, or what repairs were made.
That being said, from sitting for a while, the tires have some dry rot, and I know that’s an issue. I rotated the tires, and although I got a new vibration at 40 mph from doing so, the 50 to 60 vibration was still the same, making me think it was a separate thing from the tires, otherwise I would have felt the vibration move around or change? .But, tires are on my list to get done and still could be the vibration problem…not ruling that one out, so thanks.
As far as a misfire, that also makes sense. I did not inspect or change the plugs or wires, which is usually one of the first things I do on a new-to-me vehicle. They aren’t coil packs or coil on plugs, so the cost shouldn’t be too bad if I were to replace the wires and plugs. My only fear is it being a triton motor. Lol. I had ane350 with the 5.4 and had a plug blow on me. And then I read everywhere that the plugs are real easy to snap off in the thread. I guess I’ve been avoiding that for obvious reasons. Plus, it just looks like a bear trying to get to the plugs, with all the crap on top and in the way, especially the further back ones. But it can be done and is probably something I should do eventually. While on the topic, I read you should be careful on what plugs you use…what is recommended? But I was also thinking, I get the vibration worse when accelerating, at 50 and up to 60, which, the idea of the leaner mix when the egr opens, would make sense (btw, would have never thought of that…good idea!) But it still vibrates without giving it gas, which would make me think it’s not that. But let me ask you this, if that was the case, and, say, I cut power to the egr solenoid so it wouldn’t open the egr valve when it was supposed to, if I noticed any change in the vibration, that would pretty much point to what you are saying, right, and it would be ignition related, like a bad plug or wire).
Another thing I wanted to try was take this little camera I have (it’s like a gopro knock off I got for 20 bucks). Was gonna put it in different places to see if I can locate more specifically where the vibration is coming from. It’s hard when your dealing with a speed related issue…but with the camera, I can put it close to say the driveshaft or the trans, etc and see if I hear anything.
Thanks so far for the replies and will keep you all posted if I find out anything new.

 

I SEEN YOUR POST AND I HAVE THE SAME EXACT PROBLEM I HAVE A 2001 E-350 SUPER DUTY 5.4 L 2V. I WAS DRAWN TO YOUR POST FOR THE SIMPLE FACT OF I HAVE ALWAYS THOUGHT IT WAS IN THE DRIVE SHAFT. WHAT REALLY BLOWS MY MIND IS I HAVE A 1998 5.4 L 2V SAME VAN ONLY THE 2001 IS SUPER DUTY BOTH CARGO VANS AND THEY BOTH DO THE EXACT SAME DAM THING THE NOISE THE VIBRATION EVERYTHING I HAVE DONE I HAVE COME UP SHORT ON GETTING THIS NOISE TO GO AWAY AS FAR AS TIRES BEING THE PROBLEM I JUST DONT SEE THAT BEING THE ISSUE BEING I HAVE HAD DIFFERENT TIRES ON BOTH VANS. THE 2001 HAS A COMPLETE NEW FRONT IN "DUE TO THE ISSUE" SO IT BEING TH FRONT IN IS OUT OF THE ISSUE IN MY MIND AND WHEN I SAY ALL NEW FROM BALL JOINTS TO TIE RODS TO PITMAN ARM BUSHING STABELIZER BUSHING ROTORS CALIBERS BRAKES EVERYTHING IS NEW ALL MOTORCAFT ALSO CAUSE THAT ALL I EVER PUT IN MY VANS. ANY IN PUT WOULD BE GREATLY APPERCIATED THAT IS FROM FROM PEOPLE THAT KNOW FORDS!! NOT JUST MANUAL READERS THANKS