Mercury V8 250 User Manual

1 - Port fuel rail
2 - Starboard rail and injectors
3 - Fuel inlet from vessel
4 - Starboard rail hose quick‑connect
5 - Filter to fuel supply module (FSM) hose
6 - FSM
7 - Manifold reference base hose
8 - FSM T‑fitting
9 - Manifold reference quick‑connect
10 - Port rail hose quick‑connect
11 - Port rail hose
12 - Water‑separating fuel filter
13 - Manifold reference
14 - Starboard rail hose
15 - High‑pressure to fuel rails
16 - Fuel pressure regulator
17 - Fuel cooler
18 - High‑pressure fuel pump
19 - Siphon tube
20 - Fuel cooler
21 - Fuel lift pump
22 - Recirculation check valve
Fuel Supply Module (FSM)
Fuel Supply Module (FSM) Description
The FSM contains the fuel lift pump, high‑pressure fuel pump, fuel pressure regulator, and the fuel cooler. The filling of the
FSM is provided by the positive displacement fuel lift pump. Modulation of the fuel lift pump is not required.
The volume of entrained air in the FSM, high‑pressure fuel line, and fuel rail must be purged to allow the fuel to reach the top
fuel injector on the fuel rail. When the FSM is properly purged, it is almost always completely filled. The fuel lift pump and the
high‑pressure fuel pump are both powered by the same electrical circuit inside the FSM. Power from the fuel pump relay
activates the fuel lift pump and the high‑pressure fuel pump. Fuel pressure is controlled by the fuel pressure regulator located
inside the FSM.
Cooling of the fuel occurs with a bi‑level heat transfer. Inside the FSM are four metal tubes: two that are large diameter and two
that are smaller diameter. The smaller diameter tubes are inside the large diameter tubes. The large diameter metal tubes pass
water that cools the reservoir fuel and the fuel that passes through the smaller diameter tubes from the high‑pressure pump
and fuel pressure regulator.
a - Fuel pressure regulator manifold reference port
b - High‑pressure fuel out port
c - Fuel cooler water out port to the water pump indicator
d - Fuel lift pump (from vessel)
e - Fuel cooler water in port from strainer
f - Fuel cooler fuel tube
c
f
a
b
c
d
e
e
c
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Fuel System
90-8M0146617 eng JULY 2018 © 2018 Mercury Marine Page 7A-7

Mercury V8 250 Specifications

General

Brand	Mercury
Model	V8 250
Category	Outboard Motor
Language	English