TM 10-3930-669-34 4.  EXCESSIVE BLACK OR GREY SMOKE (CONT). KNOWN INFO Injection pump OK. injection pump timing OK. Engine compression OK. Valves and valve springs OK. Piston ring(s) OK. POSSIBLE PROBLEMS TEST OPTIONS Verify repair. REASON FOR QUESTION If   engine   does   not   exhaust   black   or gray    smoke    excessively,    fault    has been corrected. 2-46