When youtry to locate the exact source of the noise, try using a long socket extension or long screw driver like a stethwscope. Sound travels better and faster through dense objects. Since steel is much denser that air, when one end of the extension is held against the injector and the other end against your ear, youcan zero in on the cylinder. This is also effective for identifyiong the source of bearing whine in the belt driven component train.

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Deezel
87 300TDT
150,000 miles