ARMY TM 9-2815-256-24 AIR FORCE TO 38G1-96-2 MARINE CORPS TM 2815-24/5P Table 3-2.  Troubleshooting - Continued MALFUNCTION TEST OR INSPECTION CORRECTIVE ACTION Step 4. Defective fuel injection pump. a.    Remove and test fuel injection pump.  Refer to paragraphs 3-27.1.  and 3-27.7. b.    Repair or replace fuel injection pump.  Refer to paragraph 3-27. 12.  BLUE EXHAUST SMOKE. Step 1. Check for blocked air intake system. Remove blockage as found.  If no blockage is found, do step 2. Step 2. Check for defective intake or exhaust valve seals or valve guides. a.    Repair or replace defective components.  Refer to paragraph 3-34. b.    Disassemble and  inspect  valve  seals  and  guides.   Refer  to  paragraphs  3-34.3.  and  3-34.4.   if  not defective, replace engine. 13.  ENGINE KNOCKS. Step 1. Improper fuel injection pump timing. Check fuel injection pump timing.  Refer to paragraph 3-28.  If improperly timed, do step 2. Step 2. Check for defective fuel injector. a.    Remove, clean, and test fuel injectors.  Refer to paragraphs 3-29.1., and 3-29.2., and 3-29.3.  If not defective, do step 3. b.    Replace fuel injectors.  Refer to paragraph 3-29. Step 3. Check engine compression. a.    Check compression.  Refer to paragraph 3-5. b.    If engine defective, replace engine. 14.  ENGINE MAKES ABNORMAL NOISE. 3-11