>> When I start up my van in the morning, I sense only 3 pistions are
>> firing.  When I rev it a  little, it's even more obvious not all 4
>> pistons are firing.

While I don't know what this sounds like, it could be a stuck lifter.
The engine sounds horrible until the lifter gets unstuck, then it sounds
fine. Try an oil change and see if that makes it go away.

Scott
'85 Westie
Seattle