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| Home / Outboard Engines / Mercury Engines / Mercury 20 MLH |
Mercury 20 MLH Troubleshooting
| Engine won't start or difficult to start |
No fuel in fuel tank - Fill gasoline up.
Wrong grade of gasoline - Change fuel.
Air trapped in fuel system - Bleed air.
Spark plug wiring connection is defective - Inspect spark plug wiring connection, change or repair.
Damaged spark plug - Change spark plug.
Plugged fuel filter - Fuel filter needs changing.
Fuel lines clogging - Fuel lines must be clean.
Discharged or worn battery - Recharge or replace battery.
Bad harness connections - Check wiring harness connections.
Defective ignition system - Check ignition system components and change if necessary.
Pulse fuel pump is defective - Pulse fuel pump need to be replaced.
Electric fuel pump is faulty - Replace electric fuel pump.
ECM failure - Replace ECM.
| Engine starts and then stalls |
Faulty spark plug - Spark plug need to be replaced.
Ignition coil is defective - Ignition coil must be replaced.
Pulse fuel pump is defective - Pulse fuel pump need to be replaced.
Fuel system clogging - Fuel system need to be cleaned.
Final fuel filter is dirty - Install new final filter.
Defective electric fuel pump - Replace electric fuel pump.
| Engine runs unevenly |
Ignition system is defective - Inspect ignition system and change failed components.
Clogged or defective fuel pump - Service or change fuel pump.
Restricted fuel lines - Service fuel lines.
Dirty fuel filter - Fuel filter needs to be replaced.
| Engine overheating |
Engine overloaded - Reduce engine load.
Wrong ignition timing - Ignition timing needs to be set properly.
Faulty thermostat - Change thermostat as required.
Faulty water pump - Water pump need to be replaced.
| Engine knocking or noise |
Stale or low octane fuel - Use correct fuel.
Engine overloaded - Reduce engine load.
Incorrectly adjusted low idle speed - Correct idle settings.
Fuel pump is faulty or clogged - Service or change fuel pump.
Worn crankshaft or main bearings - Change or repair worn components.
Worn cylinder bore or piston rings - Replace faulty parts.
| Engine power is insufficient |
Fuel pump is dirty or defective - Check fuel pump and change if required.
Ignition failure - Inspect ignition system and change failed components.
Faulty powerhead parts - Defective parts need to be replaced.
Failed switch box, stator, or coil - Change faulty components.
Low compression - Correct.
Fuel delivery problem - Check and repair.
Manifold fuel leak - Repair leaks.
Vapor separator is flooded - Normalize vapor separator functions.
| Excessive fuel consumption |
Loose or defective spark plug - Re-tighten or replace spark plug.
Sleeve, rings, or piston are damaged - Change faulty components.
Engine is overloaded - Reduce engine load.
Clogged or defective fuel injectors - Clean or replace fuel injectors.
| Trim motor runs but system does not move |
Oil level is low - Check oil level and add oil as required.
Damaged pump assembly - Inspect pump and change as required.
Manual release valve leaking - Close the valve fully or replace it.
Motor or pump driveshaft faulty - Change worn component.
| Trim does not fully up or down |
Defective pump assembly - Replace pump.
Tilt ram piston ball is not positioned correctly - Clean or repair.
Tilt ram piston O-ring is worn - Install new O-ring.
Lack of oil - Checking oil level and add if necessary.
Lower check valve is not properly secured in port side trim ram - Install valve correctly.
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