TM 10-3930-671-24 C. Engine Runs "Rough" With Excessive Vibration NOTE A characteristic of a fuel injection pump is that if engine misfiring occurs, and it is traced to a certain cylinder in which no combustion is taking place, the cause might be an injector sticking open in the cylinder which immediately precedes that cylinder in the engine firing order. During injection to the cylinder which has the injector sticking in the open position, the fuel rushes into that cylinder with no restriction whatsoever, causing a scavenging effect in the pump distributor rotor and a void which cannot be recharged to a sufficient degree to provide opening pressure of fuel to the following injector. Hence, no combustion can take place. Please note this well, as knowledge of this characteristic might provide a great saving in service time in such a situation. 1. Misfiring cylinder(s) Loosen fuel line to injector one at a time. No noticeable change indicates that cylinder is misfiring. Clean and test injector for pressure, leakage, and spray pattern. 2. Too low operating temperature Check thermostat. (below 1650F) 3. Air in fuel lines Check connections; bleed fuel system. 4. Clogged air cleaner Clean and service air cleaner; tighten connections. 5. Engine idles too slowly Adjust to correct idle speed specification. 6. Poor fuel Use diesel fuel that meets specifications. 7. Faulty head gasket Replace. D. Loss of Power 1. Wrong injection pump timing Retime pump to engine per specifications. 2. Air in fuel lines Check connections and bleed fuel system. 3. Clogged or dirty fuel filters Clean primary filter and replace secondary filter, if necessary. 4. Restriction in air flow Service air cleaner and connections. 5. Poor fuel Use recommended diesel fuel specification. 6. Poor compression See recommendations under item G. 7. Injector nozzles faulty Clean and test faulty nozzle for pressure leakage and spray pattern. 8. Injection pump faulty Remove and have checked at an authorized service center. E. Overheating 1. Lack of coolant/low coolant level in Add coolant. Tighten hose connections; repair leaks as required. radiator 2. Engine oil level is low Add oil; inspect for cause. 3. Fan belt(s) slipping Inspect belt condition; adjust tension. 4. Fan installed backwards Remove and install correctly. 5. Radiator fins plugged (dirty) or core Clean cooling system or replace radiator. clogged 6. Rust and scale buildup in radiator or Clean cooling system or overhaul. engine block 7. Overloading of engine Reduce load. Keep engine speed up. 8. Thermostat sticking or inoperative Remove, clean, check/replace thermostat. 9. Fuel injection timing wrong Retime pump per specifications. 10. Excessive back pressure in exhaust Inspect/clean muffler and exhaust system. system 11. Leaking exhaust pipe Repair or replace. 12. Water pump faulty Repair or replace. F-69