Greetings from a newbie...
I have a 4D55 in an '86 Ranger. Recently, it has aquired a nasty vibration. At first, the vibration came and went with a periodicity dependent upon engine RPMs.
A few days later, the vibrations mostly faded away.
But it is now back (at least at some RPMs) and more of a steady vibration.

There are some other occasional noises - something more of a brief screech. Not horribly different than the sound of somebody dropping a screwdriver on the valve cover. (Nope, no miscellaneous screwdrivers lying around in there.) <img src="/forums/images/graemlins/shame.gif" alt="" />

Per mechanic advice (primarily a gas mechanic), the truck has a new turbo. The muffler has also been removed.

The vibration is present whether I'm in gear or not.
There are no obvious motor mount problems.
Motor was rebuilt about 40K miles ago, tranny about 2K ago.
Best MPG pre motor rebuild: 34 <img src="/forums/images/graemlins/kewl.gif" alt="" />
Best MPG post motor rebuild: 27 <img src="/forums/images/graemlins/frown.gif" alt="" />
Don't think it has the power it should have, either.

So now I come to all of you, looking for advice.