Yanmar 4TN78T Troubleshooting
| Engine Model: Yanmar 4TN78T |
| Engine Type: 4-cycle 4-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 100.1 cu.in (1.64 L) |
| Rated Engine Power: 39 Hp (29 kW) at 2700 rpm |
| Aspiration Type: Turbocharger |
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| Engine starts hard or will not start |
Fuel filter plugging - Clean the filter element.
Air in the fuel system - Air bleeding.
Damaged or dirty injection nozzles - Install a new kit of correctly balanced nozzles.
Defective fuel injection pump - Replace or rebuild injection pump.
Incorrect valve timing - Correct or change timing gear.
Clogged fuel pipes - Service or replace fuel pipes.
Unadjusted injection timing - Set the injection timing correctly.
Excessive wear of piston rings and cylinder - Replace faulty parts.
| Engine starts and stops suddenly |
Fuel filter plugging - Change filter element.
Defective fuel injection pump - Change pump or rebuild it.
Air filter is clogged - Service air cleaner.
Improper nozzle opening pressure - Adjust as recommended.
| Engine stalls after running |
Timing of fuel injection pump is incorrect - Adjust according to specifications.
Fuel filter element is clogged - Service the filter.
Coolant temperature is low - Warm up to required temperature.
Stuck or burnt injection nozzle - Clean or replace injection nozzles.
Wrong adjustment of low idle speed - Correct the settings.
Incorrect valve clearance - Adjust to proper valve clearance.
Fuel injection pump failure - Repair or install new pump.
Faulty or dirty injection nozzles - Install a new kit of correctly balanced nozzles.
Restricted fuel hoses or lines - Clean fuel hoses and lines.
Clogged air filter element - Clean or replace element.
Blown cylinder head gasket - Install a new gasket.
Incorrect injection timing - Adjust injection timing as required.
Fuel injection pump failure - Rebuild or install a new injection pump.
One of moving engine parts has broken - Replace or repair damaged components.
Dirty radiator core or defective radiator cap - Install new cap or clean radiator.
Insufficient coolant fluid - Fill radiator to proper level and check components for faults.
Fan belt is worn or faulty - Fan belt must be replaced.
Lack of engine oil - Add oil to the engine crankcase.
Cylinder-head gasket is leaking - Replace cylinder head gasket.
Incorrect injection timing - Check injection timing adjustment.
Not enough oil in the engine - Add oil to the engine crankcase.
Oil pump is defective - Inspect and change as required.
Engine oil filter is plugged - Replace or clean engine oil filter element.
Relief valve is stuck or broken - Change or clean relief valve.
Excessive oil clearance of crankshaft bearing - Check and replace or repair defective parts.
Excessive crankpin bearing clearance - Check and replace or repair defective parts.
| Engine consuming too much oil |
Oil leaking: Gaskets or seals can be faulty - Change worn parts according to specifications.
Improper oil viscosity - Use oil of proper viscosity.
Stuck or defective piston rings - Piston rings replacement required.
Damaged valve stems or valve guides - Replace the valves.
Worn pistons or cylinder liners - Check liners and pistons, change as required.
Coolant temperature is low - Warm up engine as required.
Engine oil level low - Fill up the oil to required level.
Incorrect adjustment of fuel injection pump timing - Check the fuel injection pump timing adjustment.
Piston wear or scoring - Pistons replacement required.
Misaligned or defective connecting rod - Align or replace connecting rod.
Low battery capacity - Recharge the battery.
Battery won’t hold charge - Service or replace the battery.
Disconnected wires or corroded battery terminals - Connect wires properly or change terminals.
| Starter motor is not working |
Battery is discharged or defective - Replace or charge as required.
Battery cables are disconnected or improperly connected - Inspect cables and connect properly.
Battery voltage is low - Battery is drained, charge it.
Starter motor failing - Starter should be replaced.
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