shudder at specific rpm

[marcbeaudry]

So - the shudder syndrome - it's been discussed and talked about ad nauseum - but my symptoms seem somewhat different . specifically between 1750-1950 rpm i get a shudder - doesnt matter what gear , if i accelerate hard - and the rpm's go up fast - you just 'shorten' the time when it will shudder - but it will do it in all gears - OD on or off, accelerating while holding the brake , it'll do it on decel . not in park, not in neutral.
i did all the factory recommended service maintenance to it as soon as i got it, fluid is up, fresh trans service, new vehicle to me and it's done it since day 1.

any thoughts at all ?

98' -4.6l 4x4 XLT

 

[Blwnl36]

my truck does it too. but below 1k rpm in od. When driving and steeping on the accelerator and truck wont Downshift from OD and rpms are below 1k it seem to buck. none answered me yet. Hopefully its the same issue

 

[masterhacker]

Maybe your clutches in the rear end is shot, i remember seeing a ford tsb about a similar problem

 

[98EXPY 5-0]

Not quite as specific as yours, but I had a low RPM bucking that would go away at higher RPMS (usually above 2k). Thought it was the Torque Convertor. Ended up being some bad coils. The thing that told me was that instead of babying it through the shudder, I finally just forced it to shudder, which caused the check engine light to flash.

If you have a code reader that can do pending codes, you can probably scan while driving after it has bucked a few times and see if you get a misfire code.

 

[masterhacker]

I do remeber having a similar problem now that you bring up the coils, some moisture got trapped in one of the plug boots so at low rpms it would short out, I had to blow out all my coils/spark plug holes with a air compressor and that took car of it

 

[98EXPY 5-0]

Before figuring it out, mine was so bad that I drove around in 2nd gear all the time. I would only let it go to third if I was doing 60 or more to keep the RPMs up. Then I replaced all the coils and plugs and for a month it was good. Then it started happening again, but to a much less extent. I scanned it and number 3 was misfiring. I pulled the coil and the boot had gotten hung up when I installed it and didn't fully seat. It was all deformed, so I took one of the rubber boots from another coil and replaced it. I also packed it inside and out with dielectric grease. Runs great now.