TM   9-2815-202-34 2-5. MALFUNCTION, PROCEDURES TEST  OR  INSPECTION,  AND  CORRECTIVE  ACTION (Cont) MALFUNCTION TEST  OR  INSPECTION CORRECTIVE  ACTION 3. ENGINE  ROTATES  BUT  FAILS  TO  START Step 1. Check main fuel supply line valves are open and fuel supply level inadequate. Step 2. Check fuel pump for damaged drive shaft or drive coupling. insert end of 1/8 inch diameter  wire  through  one  of  the  pump  flange  drain  holes.  Crank  engine momentarily ;note if slight vibration is felt in wire. If wire vibrates, drive shaft is all right. If no vibration is felt, replace fuel pump. WARNING Fuel spraying on hot components is an extreme fire hazard.  Control  leakage  immediately  to  prevent  injury. Step  3.  Check  for  air  in  fuel  system. a. Disconnect fuel return line and drain into a bucket. WARNING Protective fan screens must be installed prior to doing maintenance  in  the  engine  compartment  when  engine is running or when engine is in ground hop mode. Contact  with  rotating  fan  can  cause  injury  (reference FM   21-11). b. Crank engine momentarily. Observe fuel return flow. Uneven flow or bubbles in fuel indicate air in fuel system. Step 4. Check for contaminated fuel (water in fuel). a. Drain and clean fuel strainer and filter. b. Replace with new element as required manual). (Refer  to  vehicle  type-20  maintenance 2-4 Change 1