1990 jeep wrangler with the 2.5l 4cyl engine. it was rebuilt about 10 years ago its got 100,000 ish on the engine. About 4 years ago it started making this noise. Some people thought it was a diesel engine. oil pressure test confirms somethings up. The needle was some what jumpy. It only does it when the engine is warmed up. I suspect its a lifter issue or a spark knock.
Any ideas?