Mercury 3.0 Liter Service Manual download pdf (Page 41)

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Miscellaneous Checks

Mechanical Checks

Marine engines are, by the nature of their environment, engineered to be

trouble-free, durable power plants. The experienced mechanic, when

investigating a possible marine engine problem, will isolate boat related

support systems from the marine engine. This can be accomplished through

the use of a remote fuel tank filled with fresh fuel and utilizing a known good

fuel line/primer bulb assembly. If the engine runs properly after being

connected to the remote fuel tank, the mechanic’s troubleshooting time will be

spent in the boat checking for pinched/damaged fuel lines, stuck anti-siphon

valves, plugged filters or draining fuel tanks of poor quality fuel.

If the engine does not run properly on the remote fuel tank, the mechanic can

sometimes further isolate the problem by squeezing the fuel line primer bulb. If

the engine runs properly, the problem lies in fuel delivery – defective or weak

mechanical fuel pump, electric fuel pump, plugged filters or leaking fuel lines.

Poor running characteristics of a particular outboard can usually be identified

as the result of a problem in one of three areas: Mechanical, Electrical, or Fuel

Management.

Before disassembling and replacing EFI components, the experienced

mechanic will isolate the problem(s) to one (or more) of the 3 aforementioned

areas.

Mechanical – A compression check should be performed with the powerhead

warm (if possible), all spark plugs removed, the throttle shutters held wide

open and a fully charged battery employed for cranking duties. Normal

compression psi should be within specifications. Inspect powerhead for

leaking seals, gaskets or broken/disconnected throttle spark linkages.

Due to the precise fuel delivery characteristics of electronic fuel injection and

its dependency on many sensors to determine the correct fuel/air ratio during

all conditions, IT IS IMPERATIVE THAT SET-UP PROCEDURES BE

FOLLOWED EXACTLY AS STATED IN FACTORY SERVICE LITERATURE.

Fresh Quality Fuel

Using a remote fuel tank containing a major brand of premium unleaded

gasoline, test run the outboard to eliminate any problems related to restricted

fuel supply (clogged lines, malfunctioning anti-siphon valve, etc.) and/or

marginal gasoline.

Notes

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Mercury 3.0 Liter Service Manual Page 41