A little history first. About 6 months ago the crank pulley went out. While pressing the new one on we had to tap on the new pulley, press further, and tap some more. About a month later, the 4.0 developed a slight tap that was in unison with rpms. The tap was light, and many said it was probably excessive end play. Today, under slight acceleration, it sounded like something let loose and a very loud tap has developed. No chage in idle, oil pressure, or temp. But it is very loud, loudest on slight acceleration, meaning at no throttle(coasting) or medium throttle it quiets down. I drove approximately 60 miles like this, babying it all the way, but at highway speed. It got no worse during or after the trip. I'm guessing rod bearing??? I will try to find out more tomorrow by pulling plug wires to isolate a cylinder. My question is... because of my stupidity during the crank pulley repair, is it worth trying to fix one cylinder? Are the others far behind? Or am I totally off base. Any input will be greatly appreciated, as this is my DD. Oh, and yes oil is fairly new and level is good. Thanks.