Mercury 250XL Troubleshooting
| Engine Model: Mercury 250XL |
| Engine Type: 4-stroke 8-cylinder DOHC 32-valve gasoline outboard engine |
| Total Displacement: 279 cu.in (4.6 L) |
| Rated Engine Power: 250 Hp (186 kW) at 6000 rpm |
| Fuel System: Electronic Fuel Injection (EFI) |
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| Engine doesn't start or difficult to start |
No gasoline in tank - Fill gasoline up.
Wrong grade of gasoline - Change fuel.
Dirty fuel lines - Inspect and clean.
Spark plug wire is disconnected or loose - Check spark plug wiring connection, repair or change.
Spark plug is damaged - Change spark plug.
Clogged fuel filter - Fuel filter needs to be replaced.
Vapor separator needle valve is bend or wear - Change vapor separator needle valve.
Dirty fuel lines - Fuel lines must be clean.
Fuel tank air vent clogged or closed - Fuel tank air vent need to be opened or cleaned.
Defective fuel feed pump - Replace or repair fuel pump.
Throttle cable is adjusted incorrectly or damaged - Adjust correctly or change the cable.
Valve clearance is incorrect - Adjust to proper valve clearance.
Valve timing is improper - Adjust valve timing as required.
Low fuel pressure - Check low pressure fuel pump or check system for fuel leaks.
Dirty or faulty fuel injector - Clean or install new injector.
Fuel regulator malfunction - Install new fuel regulator.
ECM failure - Replace ECM.
| Engine stalls after starting |
Defective spark plug - Install new spark plug.
Damaged or wear vapor separator needle valve - Change vapor separator needle valve.
Ignition coil is damaged - Ignition coil must be replaced.
Fuel tank air vent clogged or closed - Fuel tank air vent need to be opened or cleaned.
Fuel pump defective - Repair or change fuel pump.
Choke system malfunction - Check and repair choke system.
Valve clearance is incorrect - Need to adjust valve clearance.
Incorrect valve timing - Set the valve timing properly.
Bad or broken valve springs - Valve springs need to be changed.
Stuck valves - Valves must be cleaned.
Poor compression - Check and replace worn parts.
Dirty fuel filter - Fuel filter needs changing.
Dirty or faulty fuel injector - Clean or install new injector.
Not enough engine oil - Add oil to the engine crankcase.
Defective oil pump - Change oil pump as required.
Dirty water intake screen - Need to wash or clean.
Damaged thermostat - Replace thermostat.
Defective water pump - Replace water pump.
Ignition failure - Inspect ignition system and change faulty parts.
Dirty or damaged fuel pump - Check fuel pump and replace if necessary.
Worn or damaged vapor separator needle valve - Install new needle valve.
Dirty fuel lines - Fuel lines must be clean.
Closed or restricted fuel tank air vent - Open or service air vent.
Clogged fuel filter - Replace fuel filter.
Intake manifold air leaks - Change intake manifold gasket.
Dirty water intake screen - Need to wash or clean.
Throttle valve and throttle link are defective or worn - Replace faulty components.
Damaged or clogged fuel injector - Clean or install new injector.
Engine overloaded - Load reducing required.
Fuel injector or fuel pump is clogged - Replace or clean if necessary.
Ignition timing is wrong - Adjust ignition timing correctly.
Faulty thermostat - Replace thermostat.
Faulty water pump - Change water pump as required.
Propeller selection improperly - Install correct propeller.
Damaged or improper size of propeller - Replace propeller.
Outboard engine is positioned too low or too high - Position the engine correctly.
Not enough engine oil - Checking oil level and add if necessary.
Faulty oil pump - Change oil pump as required.
Dirty water intake screen - Wash or clean as required.
Valve setting is wrong - Set the valves properly.
| Abnormal engine noise or knocking |
Stale gasoline - Change gasoline.
Engine overloaded - Reduce load.
Wrong adjustment of low idle speed - Correct idle settings.
Fuel pump is clogged or faulty - Service or change fuel pump.
Main bearings or crankshaft wear - Change or repair worn components.
Worn cylinder bore or piston rings - Replace defective parts.
Fuel lines clogging - Fuel lines must be clean.
Defective fuel injector - Replace fuel injector.
Fuel pump is clogged or faulty - Test fuel pump and change if necessary.
Defective ignition - Check ignition and replace faulty components.
Cylinder head gasket is defective - Install new cylinder head gasket.
Powerhead parts are worn out - Replace defective parts.
Burned or stuck valves - Clean or change valves.
Improper propeller diameter or pitch - Install correct propeller.
Damaged or bent propeller - Replace propeller.
Outboard motor mounting height is set incorrectly - Adjust the engine to correct transom height.
Incorrect trim angle - Make the correct trim angle adjustment.
| Engine uses too much fuel |
Fuel injector is faulty or clogged - Clean or replace as required.
Spark plug is loose or defective - Spark plug need to be tightened or replaced.
Worn piston, rings, or sleeve - Change faulty parts.
ECU is faulty - Change electronic control unit.
Damaged or bent propeller - Replace propeller.
Propeller shaft damaged - Propeller shaft needs to be replaced.
Weeds clogs the propeller - Remove weeds from propeller.
Engine mounting bolt is not tightened - Tighten the bolt as required.
Damaged or loose steering pivot Tighten or replace.
Low battery capacity - Battery is drained, recharge it.
Battery discharges quickly - Battery needs service or replacement.
Disconnected wiring or bad battery terminals - Check wire connections and change or service terminals.
Faulty starter motor - Repair or change starter.
| Trim motor runs but trim system does not move up or down |
Insufficient oil - Fill up oil.
Defective pump assembly - Inspect pump and change as required.
Leakage of manual release valve - Close the valve fully or replace it.
Faulty pump driveshaft or motor - Replace worn component.
| Trim cannot be fully up or down |
Defective pump assembly - Replace pump.
Tilt ram piston ball is displaced - Service or repair.
Damaged tilt ram piston O-ring - Replace O-ring.
Oil level low - Fill up oil to required level.
Lower check valve is not properly secured in port side trim ram - Secure valve properly.
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