1994 Explorer engine tapping loudly on idle when warm

[abrush]

It's been close to 2 years since I dropped this 1994 Explorer engine in my 1988 Bronco II. Up until this time I have been driving trouble free. I have put 20,000 miles on the engine since the swap with it currently having 170,000. However about a week ago I noticed that when I come to a stop with the engine just idling I hear a very loud tapping sound. The engine only does this when fully warmed up and only when idling. When I rev the engine or accelerate it immediately stops. I don't have any loss of power or have noticed any other symptoms. Everything I researched had the opposite effect with the engine tapping on acceleration. I'm getting a little worried I might be throwing my second 4.0 in this Bronco II. Anyone have any advise as to what could be causing this noise? I'm having a hard time telling if it is coming from the top or bottom end but I'm thinking more on the bottom side.

 

[IMenriched]

try changing the oil and filter....maybe you've got a compromised filter

 

[abrush]

I have never heard of that one before. I pulled off the driver side rocker cover the other day to see if there was any play in the rocker arms in case it is lifter noise but there wasn't on that side. I will have to pull off the other side to check as well. The more research I've done I have found these motors had premature lifter wear because of poor oil circulation so I am thinking this could be my problem. Any one else have any ideas?

 

[dangerranger83]

Dirty lifters mabey. ATF fluid should clean them up right up.