TM 10-3930-669-34 4. EXCESSIVE BLACK OR GREY SMOKE (CONT). KNOWN INFO TEST OPTIONS Injection pump OK. Visual inspection. Injection pump timing OK. Engine compression OK. REASON FOR QUESTION POSSIBLE PROBLEMS If valves or valve springs are faulty, engine will exhaust black Valves or valve springs faulty. or grey smoke excessively. Piston ring(s) faulty. KNOWN INFO TEST OPTIONS Injection pump OK. Visual inspection. Injection pump timing OK. Engine compression OK. REASON FOR QUESTION Valves and valve springs OK. If piston ring(s) is faulty, engine Possible problems will exhaust black or grey smoke . excessively. Piston ring(s) faulty. 2-44 (Para 3-6 or 3-5). (Para 3-7 and 3-13  or  3-13