Yanmar 3TN78 Troubleshooting
| Engine Model: Yanmar 3TN78 |
| Engine Type: 4-cycle 3-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 69.9 cu.in (1.15 L) |
| Rated Engine Power: 23 Hp (17 kW) at 2500 rpm |
| Aspiration Type: Naturally aspirated |
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| Diesel hard to start or doesn't start |
Fuel filter plugging - Service or replace the filter.
Air in the fuel pipes - Bleed the fuel pipes.
Dirty or faulty injection nozzles - Clean or change injection nozzles.
Fuel injection pump is not operating properly - Replace or repair injection pump.
Valve timing is out of adjustment - Use correct valve timing adjustment.
Dirty fuel pipes - Service or change fuel pipes.
Unadjusted injection timing - Set up as recommended.
Piston rings and cylinder are worn - Change defective parts.
| Diesel starts but immediately shuts off |
Fuel filter element is clogged - Change the filter element.
Fuel injection pump malfunctioning - Rebuild or change fuel pump.
Restricted intake air - Replace air filter element.
Incorrect nozzle opening pressure - Set it correctly.
| Engine stalls during operation |
Timing of fuel injection pump is incorrect - Adjust fuel injection pump as required.
Dirty fuel filter - Clean or change the filter.
Engine is not warmed up to the required temperature - Warm up engine as required.
Injection nozzles sticking or clogged - Clean or change injection nozzles.
Low idle speed set incorrectly - Adjust the low idle speed.
Excessive valve clearance - Need to adjust valve clearance.
Damaged fuel injection pump - Replace or repair injection pump.
Damaged or dirty injection nozzles - Test injection nozzles and change if necessary.
Fuel hoses or lines are dirty - Fuel hoses and lines must be clean.
Plugged air filter - Clean or change.
Cylinder-head gasket is leaking - Replace the gasket as required.
Injection timing is improper - Set the injection timing correctly.
Fuel injection pump is broken - Replacement or repair required.
One of moving engine parts has broken - Repair or replace defective parts.
Defective radiator cap or clogged radiator core - Change cap or clean radiator.
Coolant level is low - Top up coolant fluid and check system for leaks.
Loose or damaged fan belt - If necessary, replace the belt.
Engine oil insufficient - Need to add engine oil.
Cylinder head gasket is defective - Cylinder-head gasket replacement required.
Wrong injection timing - Set up as recommended.
Low crankcase oil level - Add oil to the engine crankcase.
Oil pump is worn or damaged - Remove and inspect oil pump.
Dirty oil filter - Clean or change engine oil filter.
Worn or dirty relief valve - Replace or service relief valve.
Excessive oil clearance of crankshaft bearing - Inspect and change or repair worn components.
Clearance of crankpin bearing is excessive - Test and repair or replace worn parts.
| Engine using too much oil |
Oil leakage: Worn seals or gaskets - Worn parts need to be replaced.
Crankcase oil too light - Fill up with the correct oil viscosity.
Piston rings are defective or worn - Change piston rings.
Damaged valve guides or valve stems - Valves replacement required.
Damaged cylinder liners or pistons - Inspect liners and pistons, change as necessary.
| Engine knocking sound or abnormal noise |
Engine is not warmed up to the required temperature - Normalize the temperature by warming up the engine.
Engine oil level is low - Need to add engine oil.
Improper fuel injection timing - Set up as recommended.
Broken or worn pistons - Pistons need to be replaced.
Connecting rod is worn or misaligned - Need to change or align the connecting rod.
Low battery voltage - Low battery charging, charge as required.
Battery discharges quickly - Service or replace the battery.
Bad battery terminals or disconnected wiring - Connect wires properly or change terminals.
Battery is low or faulty - Battery needs to be recharged or replaced.
Battery wiring is disconnected or improperly connected - Inspect wiring and connect as required.
Low battery voltage - Recharge the battery.
Starter motor is faulty - Starter should be changed.
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