1. Poor Quality Fuel
Remove the fuel from the fuel tank. Install a new fuel filter element. Put a good grade of clean fuel in the fuel tank.
2. Fuel Pressure Is Low
Make sure there is fuel in the fuel tank. Look for leaks or severe bends in the fuel line between fuel tank and fuel transfer pump. Look for air in the fuel system. Check fuel pressure. The outlet pressure of the fuel transfer pump at full load speed is 205 ± 35 kPa (30 ± 5 psi).
If fuel pressure is lower than above pressure, install a new fuel filter element. Inspect the fuel bypass valve for free movement. Install a new fuel bypass valve if necessary.
3. Air In The Fuel System
Find the air leak in the fuel system and correct it. Remove air from the fuel system. Make reference to Removing Air From Fuel System in Testing & Adjusting.
4. Leaks In Air Inlet System
Check the pressure in the air inlet manifold. Look for restrictions in the air cleaner.
5. Wrong Fuel Setting
Make adjustments as necessary.
6. Governor Linkage
Make adjustment to get full travel of linkage. Install new parts for those that have damage or defects.
7. Defect In Timing Advance Unit
Replacement of timing advance unit is needed.
8. Wrong Valve Lash
Make adjustment according to Testing & Adjusting.
9. Defect In Fuel Injection Nozzle
Run engine at rpm that gives maximum misfiring or rough running. Then loosen a fuel line nut on the injection line for each cylinder, one at a time. Tighten each fuel line nut before loosening the next one. Find the cylinder where loosening the fuel line nut does not change the way the engine runs. Test the fuel injection nozzle for that cylinder. Install new parts where needed.
10. Wrong Fuel Injection Timing
Make adjusting to timing.
11. Fuel Shutoff Solenoid or Shutoff Linkage Causing A Restriction In The Travel Of The Shaft For The Sleeves
Check for correct full power with solenoid removed. If the engine has full power with the solenoid removed, the problem is in the solenoid or the shutoff linkage. Check for free travel of the linkage.
12. Constant Bleed Valve Stays Closed
Replace constant bleed valve.
13. Turbocharger Has Carbon Deposit
Inspect and repair turbocharger as necessary.
14. Fuel Ratio Control Has A Defect
Check fuel ratio control setting. Adjust if necessary. Check diaphragm in fuel ratio control.