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Have a 93 4.0. Engine has a knock only when it's ideling and in gear (it's an automatic) When it's ideling in park, no nock. When your driving, no nock. The sound is like a tapping coming from lower part of engine. Have not had time to really listen and find exactly where its coming from, but I know it's not lifters.
Any one had this before. Engine has 134,000 and oil has always been changed, every 3 to 4 months.
Some 4.0's have a soft/dull knock sound that is caused by the piston rings. Ford says this is normal. There is a TSB out there covering this; you may wish to do a search and see if it applies to you. FWIW, I bought my Ranger with a 4.0 new and have had a very slight and occasional sound at idle for maybe the last 120,000 miles (181,600 total on truck). It's hard to pinpoint it since it's subtile. I'm not too worried about it.
Just how loud is the knock you're getting? Is it as loud as a lifter?