Mercury Fuel Pump Assembly 861155A3

Mercury MerCruiser Quicksilver 861155A3 is a genuine OEM low-pressure electric fuel pump assembly used on select MerCruiser sterndrive and inboard fuel systems. Mercury describes it as a low-pressure boost pump kit that includes the pump, lead wires with multi-pin connector, and fittings.

Key Features

• Genuine Mercury MerCruiser Quicksilver OEM part
• Low-pressure electric fuel boost pump assembly
• Kit includes pump, lead wires with multi-pin connector, and fittings
• Commonly described as a low-pressure pump for select sterndrive and inboard installations
• OEM-threaded low-pressure pump assembly.

Engine Compatibility
Current public listings consistently tie 861155A3 to select MerCruiser sterndrive and inboard applications. Multiple sources specifically list use on MCM/MIE 4.3L, 5.0L Gen+, and 5.7L Gen+ carbureted applications, and also note boost-pump use on some MPI applications including 5.0L MPI, 350 Mag MPI, MX 6.2L MPI, and 496 Mag / 8.1S families. Because listings vary by fuel-system layout, fitment should still be confirmed by engine serial number and the installed fuel-system configuration before ordering.

Serial Number Fitment Notice
Fitment should be confirmed by engine serial number and fuel-system configuration, not by engine family alone. This pump is used across multiple MerCruiser applications, and correct use depends on whether the engine is using it as a primary low-pressure pump or as a boost pump in the matched OEM system.

When This Part Needs Replacement
Replace when the fuel pump becomes noisy, fails to prime, delivers inconsistent fuel pressure, causes hard starting, stalling, hesitation, or shows leakage or connector damage. Because this is a low-pressure fuel-delivery component, weak output can lead to poor fuel supply and driveability problems. The low-pressure role is directly supported by current OEM and OEM-focused listings.

Installation Notes
Install only on the correct MerCruiser application and verify the replacement matches the existing pump style, fittings, connector, and system role. Public listings describe this as a low-pressure pump assembly and note it includes connector leads and fittings; one current source also notes it should not be used in EFI fuel-cooler applications, so application confirmation is important before ordering.

Alternate / Superseded Part Numbers

• 861155A3
• 861155A2
• Sierra 18-8868
• Sierra 18-8868-1
• Mallory 9-35432
• EMP 1397-97000
• Pro Marine 1155

Parts Desk Insight
The key detail on 861155A3 is that it is a low-pressure fuel pump, not a generic electric pump. That matters because MerCruiser used it in more than one fuel-system role, and several listings show both carbureted primary-pump use and boost-pump use on certain MPI setups. Matching by serial number and existing pump layout is the safest way to avoid ordering the wrong fuel pump.

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