Service Bulletin

Mack Trucks, Inc.

Greensboro, NC USA Trucks
Date Group No. Release Page

5.2011 230 252 01 1(11)

Fuel System, Design and Function

MP7, MP8, MP10 US2010

Fuel System, Design and Function

This information covers the design and function of the fuel system on the MACK MP7,
MP8 and MP10 US2010 emissions engines.

Contents
• “Fuel System”, page 2

Note: Information is subject to change without notice.

Illustrations are used for reference only and can differ slightly from the actual vehicle
being serviced. However, key components addressed in this information are represented
as accurately as possible.

PV776-89019970 USA48779
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Service Bulletin 5.2011 230 252 01 2(11)

Design and Function

Fuel System
When fault tracing, it is important to understand the
function of the system in order to avoid replacing
non-defective components.

Fuel System Overview

The fuel system is electronically controlled (EMS). Fuel
injection is performed by injectors, one for each cylinder, at
high pressure. The high pressure is created mechanically
by the overhead camshaft and rocker arms. Regulation
of the fuel amount and injection point are electronically
controlled by the engine control module (ECM), which
receives signals from a number of sensors.

The engine is equipped with a hand pump, located on the

fuel filter housing.
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Service Bulletin 5.2011 230 252 01 3(11)

Fuel System Operation

W2066119

The fuel is drawn by means of the fuel pump (1) through a manual fuel pump (12) is being used, so that the fuel can
strainer (2) in the combined tank unit, up through the cooling be pumped more easily by hand.
loop (6), which cools the engine control module (ECM) (16),
and then down to the fuel filter housing (3). There the fuel The fuel filter housing (3) also has a built-in bleed valve
passes through a non-return valve (11) and a prefilter (4) (10). The fuel system is vented automatically when the
with a water separator (13). The task of the non-return engine starts. Any air in the system flows, together with a
valve is to prevent fuel from running back to the tank when small amount of fuel, back to the tank (2) via a pipe.
the engine is switched off, or when pumping by hand. When changing filters close valves (18 and 19) to prevent
The fuel pump (1) sends fuel to the fuel filter housing (3) fuel leaking out when the fuel filter is removed. Air bleeding
and through the main filter (5) up to the longitudinal fuel rail of the filter when changing filters is controlled by valves (18
(9) in the cylinder head. This rail supplies each injector (8) and 20) in the filter housing and the bleed valve (10).
with fuel via a ring-shaped channel around each injector in There is a fuel pressure sensor (21) in the fuel filter housing
the cylinder head. Overflow valve (7) controls the pressure which measures the fuel pressure after the fuel filter. A
of the fuel feed to the injectors. diagnostic trouble code (DTC) is shown on the instrument
When the aftertreatment hydrocarbon doser opens, fuel panel if the fuel pressure is less than the specification. The
flows into the valve block (26) via the fuel line (27) and on plugged outlet (22) in the fuel filter housing is used for fuel
to the doser (28). When the doser closes fuel flows back pressure measurements with an external pressure sensor
via the valve block and on through the return line (29) to or gauge.
the fuel tank.
There is a level sensor (23) inside the water separator (13)
Return fuel from the cylinder head fuel rail (9) goes through which sends a signal to the driver if there is water in the
the overflow valve (7) back to the fuel filter housing (3). The system. Draining is performed by means of a stalk (24) on
through channel in the fuel filter housing mixes the return the steering column. This opens an electrical drain valve
fuel with fuel from the tank and draws it on to the fuel pump (25) via a command from the ECM.
inlet (suction side).

There are two valves in the fuel pump. The safety valve
(14) allows the fuel to flow back to the suction side when
the pressure becomes too high, for example when the fuel
filter is blocked. The non-return valve (15) opens when the
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Service Bulletin 5.2011 230 252 01 4(11)

For the draining process to be activated, the following remains as long as the “water in fuel” indicator is above
conditions must be met: the warning level.
• Level sensor (3) in the water separator shows a high As an extra accessory there is also a fuel heater (26) that is
water level installed in the lower part of the water separator.
• Engine switched off/starter key in the drive position
The hand pump (12) is located on the fuel filter housing and
• The vehicle is stationary is used to pump fuel forward (with the engine stopped) in
• The parking brake is applied case the fuel system has been emptied.

If the engine is started during the draining process, the Note: The hand pump must not be used while the engine
draining will be stopped. A warning on the instrument panel is running.
Mack Trucks, Inc. Date Group No. Release Page
Service Bulletin 5.2011 230 252 01 5(11)

Fuel System Components

Injectors

T2054876

The unit injectors are of type E3 with two solenoid valves The ring shaped chamber for fuel supply (4) around each
for more precise injection. This ensures better combustion injector is sealed by two O-rings (5 and 6).
and minimizes particle emission, producing cleaner exhaust
gases. A unit injector principally consists of three parts:

The injectors are placed vertically at the centre of each

• Pump section
cylinder, between the four valves, and are held in place by • Valve section (actuator)
a yoke (1). The lower part of the injector is held against the
coolant jacket in the injector sleeve (2) and with O-ring (3).
• Spray atomizer section
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Service Bulletin 5.2011 230 252 01 6(11)

Within the valve section are two solenoid valves — the receives electric current and opens the needle valve (8).
waste valve (7) and the needle valve (8) with solenoid coils This releases the high pressure on to the needle valve
(9 and 10 respectively) and return springs. piston and the nozzle pin (13) opens. Atomized fuel now
sprays out at extremely high pressure into the engine
In the filling phase the pump piston moves upwards and
combustion chamber.
fuel from the cylinder head fuel rail is forced into the unit
injector. Fuel injection is stopped by opening the waste valve again,
In the waste phase the pump piston moves down and fuel which causes the pressure on the piston (12) to drop and
is forced back out into the cylinder head fuel rail. During the nozzle pin (13) closes.
this time the solenoid valve coils have no current and the The complete injection process is controlled by the engine
waste valve is open, so no pressure can build up in the fuel management system (EMS).
channel to the spray atomizer.
There are three markings on the injector electrical connector
In the pressure buildup phase, the waste valve solenoid
(16) — part number (17), trim code (18) and manufacturing
coil is energized and the waste valve closes. This allows
number (19). When replacing one or more injectors, the
a high pressure to be built up in the fuel channel (14).
engine control module (ECM) must be programmed with
Pressure also increases in the chamber (15) behind the
the new injector trim code, since each injector is unique
needle valve, which affects the needle valve piston (12)
and the engine is trimmed for optimal fuel injection and as
and prevents the needle valve (8) from opening the nozzle
low emission as possible. The trim code is programmed
pin (13).
in using the parameter programming section of Tech
Once the desired fuel pressure has been achieved, the Tool. Programming only needs to be carried out for the
injection phase begins. The needle valve solenoid coil replacement injector(s).
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Service Bulletin 5.2011 230 252 01 7(11)

Fuel Filter Housing

W2066130

There is a hand pump (1) in the fuel filter housing, which is

used to pump fuel forward if the system has been emptied,
and a non-return valve to prevent fuel from running back
to the tank when the engine is switched off. The electrical
connections (2) are for the level sensor (3) and the drain
valve (4) in the water separator (5). The prefilter (6) filters
the fuel before it passes through the feed pump, it is on the
suction side. The main filter (7) filters the fuel after it passes
through the feed pump, it is on the pressure side.

The system is equipped with a large fuel filter located on

the left-hand side of the engine. The filter insert consists
of a corrugated filter paper with a high resistance to water
and very good filtering properties. In addition, a fine-gauge
net filter on the fuel suction line in the fuel tank separates
any possible solid impurities before the fuel is pumped up
into the system.
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Service Bulletin 5.2011 230 252 01 8(11)

Fuel Pump

W2066129

The fuel pump is of the gear type and mounted on the power
steering pump (4). The fuel pump is driven by the shaft (3)
passing through the power steering pump. Sealing between
the two pumps uses an O-ring (2) positioned in a groove
in the power steering pump flange. Power transmission
between the pumps is via a floating follower (1). The pump
housing (10) and the cover (8) are cast iron. The drive gear
shaft and the pump wheel run in needle bearings (9 and 6
respectively). The pump safety valve (11) is located in the
pump housing and the non-return valve (7) in the pump
end cover. Fuel which leaks past the pump drive shaft is
drawn back to the suction side in the pump via a channel
(5). The capacity of the pump has been adapted to give
the correct pressure and flow to the injectors. Filling the
injectors requires relatively high pressure. The flow must be
large enough to even out any fuel temperature differences
in the cylinder head fuel gallery.
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Service Bulletin 5.2011 230 252 01 9(11)

Engine Control Module (ECM)

The cooling loop on the left side of the engine cools the
engine control module (ECM) using fuel from the suction
side of the fuel pump.

The engine control module (ECM) is the central part of the

injection system. It is located on the left-hand side of the
engine. The ECM receives continuous information from the
accelerator pedal and from several other sensors on the
engine. It calculates the amount and the time to inject fuel
into the cylinders. Electrical wiring to the injectors transmits
control signals to the injectors from the ECM.
W2003778
The ECM uses the flywheel sensor to monitor engine
rotation and engine speed variations during a revolution.
This allows the ECM to ensure that each injector receives
exactly the correct amount of fuel. The ECM stores
information when a fault occurs or if something in the
system is abnormal. Intermittent faults are also stored and
can be traced at a later time.

Overflow Valve
The overflow valve on the cylinder head controls the
pressure in the low pressure system, which supplies fuel to
the unit injectors and at the same time cools them. The
overflow valve has a built-in bleed valve for the fuel system.

Always replace the fuel line compression sealing

washers when:
• Troubleshooting for fuel aeration and/or
• Performing any service procedure that requires the
removal of engine fuel lines.

W2066132
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Service Bulletin 5.2011 230 252 01 10(11)

Aftertreatment Hydrocarbon Dosing System

The aftertreatment hydrocarbon doser injects diesel fuel into
the exhaust stream to increase the exhaust gas temperature
(EGT) to the range needed for forced aftertreatment diesel
particulate filter (DPF) stationary regeneration when passive
DPF regeneration is insufficient to prevent a high soot level
in the filter. The engine control module (ECM) notifies the
driver that a forced stationary regeneration is needed so the
driver can start it with a switch on the dashboard. A service
technician can start it manually in a safe location. The
aftertreatment hydrocarbon doser is also used when the
vehicle is moving to heat up the system and quickly get the
engine in compliance with US2010 emissions requirements.
At idle this is done by adjusting the engine timing and fuel
delivery to increase EGT.

Aftertreatment Hydrocarbon Dosing System Components (Previous Version)

US2010 emissions compliant engines have a continuous
air purge system which removes any fuel remaining in the
doser after aftertreatment DPF regeneration. When the
engine is operating, there is a constant flow of air through
the doser. The secondary vehicle air system, which is
off when the engine is off, supplies the air. The main
components of the previous system are:
• Chassis-mounted pressure regulator with inlet filter
• Doser-mounted check valve assembly
• Air and fuel supply tubes and hoses
• Air dryer cartridge with coalescing element
• Air shut-off valve
The secondary air system sends air to the in-line filter W2006759

mounted on the pressure regulator inlet. The pressure

regulator lowers the air pressure from chassis pressure, 1 Air Line
620-825 kPa (90–120 psi), to approximately 220 kPa (32
2 Fuel Line
psi). Air from the regulator flows through a one-way check
valve with a filter screen, which prevents back-flow to the 3 Coolant Line
regulator. Air then flows through the doser and into the
engine exhaust stream. Fuel is also sent to the doser check
valve through a one-way check valve. The ECM controls air
and fuel flow to the doser. The shut-off valve prevents air
leakage into the fuel system when the ignition switch is in
the OFF position. A valve block mounted on the cold side
of the engine contains an aftertreatment hydrocarbon fuel
pressure sensor and shut-off valve.

W2066122
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Service Bulletin 5.2011 230 252 01 11(11)

Aftertreatment Hydrocarbon Dosing System Components (New Version)

The main components of the new system are: The secondary air system sends air to the in-line filter
mounted on the pressure regulator inlet. The pressure
• Aftertreatment hydrocarbon dosing module
regulator lowers the air pressure from chassis pressure,
• Aftertreatment hydrocarbon doser 620-825 kPa (90-120 psi), to approximately 220 kPa (32
psi). During air purge operation, the engine control module
• Air and fuel supply tubes and hoses
(ECM) sends a voltage signal to open the aftertreatment
• Chassis-mounted pressure regulator with inlet filter purge air valve. This allows air pressure to flow into the
aftertreatment hydrocarbon dosing module. The ECM then
• Air dryer cartridge with coalescing element
sends a signal to the aftertreatment hydrocarbon dosing
The aftertreatment hydrocarbon dosing module contains control valve that allows purge air pressure to be monitored
three non-serviceable valves, the aftertreatment fuel shutoff by a signal from the aftertreatment fuel pressure sensor to
valve, aftertreatment purge air valve and aftertreatment the ECM. The engine control module (ECM) uses this input
hydrocarbon dosing control valve, and a serviceable to determine if the system is operating correctly.
aftertreatment fuel pressure sensor.
During DPF regeneration, the ECM sends a voltage signal
to open the aftertreatment fuel shutoff valve. This allows
fuel to flow into the aftertreatment hydrocarbon dosing
module. The aftertreatment fuel pressure sensor monitors
the fuel pressure value and sends a reference signal to the
ECM. The ECM then sends a signal to the aftertreatment
hydrocarbon dosing control valve that regulates the amount
of fuel delivered to the aftertreatment hydrocarbon doser
through the air/fuel line.

W2064628

Aftertreatment Hydrocarbon Dosing Module

W2064631

Aftertreatment Hydrocarbon Doser