TM 10-3930-669-34 4. EXCESSIVE BLACK OR GREY SMOKE (CONT). KNOWN INFO TEST OPTIONS Injection pump OK. Injection pump timing check. POSSIBLE PROBLEMS REASON FOR QUESTION Injection pump timing incorrect. If injection pump timing is fault y, Low engine compression. engine will exhaust black or Valves or valve springs faulty. grey smoke excessively. Piston ring(s) faulty. 2-40 Page 2-41. (Para 4-4).