Cummins 4B3.9-G2 Troubleshooting
| Engine Model: Cummins 4B3.9-G2 |
| Engine Type: 4-cycle inline 4-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 239 cu.in (3.9 L) |
| Rated Engine Power: 47-100 Hp (35-75 kW) at 2200 rpm |
| Aspiration Type: Naturally aspirated |
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| Engine difficult to start or will not start |
Fuel filter element is dirty - Clean the filter or install new filter element.
Air in the fuel system - Air bleeding.
Defective or clogged injection nozzle - Test injection nozzles and change if necessary.
Defective fuel injection pump - Rebuild or replace pump.
Unadjusted valve timing - Use correct valve timing adjustment.
Clogged fuel pipes - Service or replace fuel pipes.
Incorrect injection timing - Use correct injection timing adjustment.
Worn cylinder or piston rings - Change faulty components.
| Diesel starts but stalls immediately |
Dirty fuel filter - Change filter element.
Faulty fuel injection pump - Repair or install a new fuel pump.
Intake air restriction - Clean or change the filter.
Nozzle opening pressure is improper - Set it correctly.
| Engine stalls while running |
Improper fuel injection timing - Adjust as recommended.
Fuel filter element is dirty - Install new filter element.
Engine is not warmed up to the required temperature - Warm up the engine.
Injection nozzles are jammed or clogged - Check injection nozzles and replace if required.
Low idle speed setting is not correct - Correct low idle adjustment.
Valve clearance is not correct - Check and adjust.
Fuel injection pump failure - Repair or install a new fuel pump.
Damaged or dirty injection nozzles - If necessary, replace with a new nozzle.
Restricted fuel lines or hoses - Fuel hoses and lines must be clean.
Restricted intake air - Service air cleaner.
Blown cylinder head gasket - Change cylinder head gasket.
Incorrect injection timing - Adjust injection timing as required.
Faulty fuel injection pump - Rebuild or change fuel pump.
One of moving engine parts is faulty - Repair or replace defective parts.
Radiator fins are clogged or radiator cap is faulty - Clean radiator or change cap.
Lack of coolant in cooling system - Fill radiator to proper level and check components for faults.
Loose or damaged fan belt - Fan belt must be replaced.
Engine oil level low - Check and refill engine oil.
Cylinder head gasket is blown - Install new cylinder head gasket.
Injection timing is improper - Use correct injection timing adjustment.
Engine oil level low - Add oil to the engine crankcase.
Oil pump is damaged - Remove and inspect oil pump.
Dirty oil filter element - Replace or service engine oil filter.
Stuck or defective relief valve - Replace or clean relief valve.
Excessive oil clearance of crankshaft bearing - Check and change or repair defective parts.
Crankpin bearing clearance is excessive - Check and change or repair defective parts.
| Engine oil consumption is too high |
Oil leakage: Worn seals or gaskets - Worn parts need to be replaced.
Wrong oil viscosity - Use oil of proper viscosity.
Stuck or worn piston rings - Change the piston rings as required.
Damaged valve stems or valve guides - Change the valves.
Cylinder liners or pistons are scored - Check pistons and liners, install new parts as required.
| Abnormal engine noise or knocking |
Engine is not warmed up to the required temperature - Warm up to required temperature.
Low engine oil level - Add oil to the engine crankcase.
Fuel injection pump timing is not adjusted - Check the fuel injection pump timing adjustment.
Pistons are scored or worn - Replace the pistons as required.
Connecting rod is defective or misaligned - Align or change connecting rod.
| Starter motor cranks slow |
Low battery voltage - Battery is drained, charge it.
Battery is draining quickly - Service or replace the battery.
Disconnected cables or faulty battery terminals - Check cable connections and replace or service terminals.
Battery is discharged or worn - Recharge or change battery.
Wiring is improperly connected or disconnected - Check wiring and connect properly.
Low battery power - Charge the battery.
Damaged starter motor - Change or repair starter.
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