TROUBLESHOOTING
TESTING AND ADJUSTING
TM 5-3805-263-14&P-2
3. MISFIRING OR RUNNING ROUGH
Cause
Air In The Fuel System
Fuel Pressure is Low
Leak or Break in Fuel Line Between
Injection Pump and Injection Valve
Defect in Fuel Injection Valve(s) or
Injection Pump(s)
Fuel System Not Timed Correctly to
Engine
Run engine at rpm that gives maximum misfiring or rough running.
Then loosen a fuel line nut on the injection valve for each cylinder,
one at a time. Find the cylinder where loosening the fuel line nut does
not change the way the engine runs. Test the injection pump and
injection valve for that cylinder. Install ‘new parts where needed.
Make adjustment to timing if necessary.
Wrong Valve Clearance
Make adjustment, See the Subject VALVE CLEARANCE in Test-
ing and Adjusting.
Bent or Broken Push Rod
Replacement of push rod is necessary.
Worn Valve Seat or Face of Valve
Reconditioning of cylinder head is needed.
Correction
Find air leak in the fuel system and correct. Remove air from fuel
system. See FUEL SYSTEM in Testing and Adjusting.
Make sure there is fuel in the fuel tank. Look for leaks or bad bends in
the fuel line between fuel tank and fuel transfer pump. Look for air in
the fuel system. Check fuel pressure at the fuel injection pump
housing. If fuel pressure at high idle is lower than 105 kPa (15 psi),
install a new filter element. If fuel pressure is still low, check the fuel
bypass valve and the check valves in the fuel transfer pump.
Install a new fuel line.
4. STALL AT LOW RPM
Cause
Idle rpm Too Low
Correction
Make adjustment to governor so idle rpm is the same as given in
FUEL SYSTEM, Testing and Adjusting.
Defect in Fuel Injection Valve(s) or
Fuel Injection Pump(s)
Run engine at rpm that gives maximum misfiring or rough running.
Then loosen a fuel line nut on the injection pump for each cylinder,
one at a time. Find the cylinder where loosening the fuel line nut does
not change the way the engine runs. Test the injection pump and
injection valve for that cylinder. Install new parts where needed.
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