I have a 1994 f-150 XLT 102000 miles and until recently she ran like a top. Took it in for a tune up because it felt like it was running on 7 cylinders. They informed me that they think it is the transmission that is doing the vibrating. She vibrates when I accelerate, and I always baby her. Just a little on the gas and I get this vibration or chatter. If I put her in nuteral the vibration goes away. Any ideas what it could be.

 

So when you put it in neutral it goes away. What about Park? Do you do any towing with it? Is it a 302 or 300 inline 6? Is the vibration RPM or speed related? Is it worse in a particular gear? Could be a multitude of things but I would tune it up for starters. New plugs, wires, cap and rotor (I think that truck still has all that). Once you do that put it under a load (in gear foot on brake little gas until it does it) in a dark spot and look under the hood for any arcing. If it smoothes out or there is no arcing there are a few other things to try. I'm not sure about that particular year but the slightly older fords use to have a control module that was attached to the base of the distributor. They are pretty expensive (or at least used to be) so I wouldn't change it until it is a last resort. I have seen that thing cause similar problems to what you describe. It typically happens after it has warmed up though at first and then all the time and eventually it just quits working. It could be the clutches slipping in the tranny. Might drop a bottle of Lucas transmission fix in it and see what happens. If it is bands slipping the Lucas stuff should if not stop it completely at least make a huge difference and if that is not the problem it won't hurt anything being in there (it is good stuff!!). I would check the engine stuff first and be sure that it is not there because a tranny rebuild is certainly not cheap.

Hope that gives some insight.

 

First of all, it is a 351 with a trailer towing package. I use to tow a trailer, but have not in at least 4 years. Under a load (foot on brake) in drive or reverse there is no vibration. It is constant when accelerating, regardless of gear and I am talking easy accerlation, same as in cruise control or less. The engine runs VERY smooth. I have not checked for arc's but will tonight. This problem is when it is warm or cold. Driving on the e-way the vibration is there, and goes away when I take it out of gear and coast, or leave it in gear and coast.

 

I would check the plug wires and the EGR first

 

well I checked for arc's in the dead of night. There were none, but there was a clicking sound. Of course, that could have been there before.

 

351 egr valves always stick for some reason. Clean it out and try it.
Alan