Group 23 EMS 2 Design and function
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Fuel control
The engine’s fuel requirement is analyzed up to 100
times per second (depending on engine rpm). The en-
gine’s injection amount and injection timing is con-
trolled electronically via fuel valves on the unit injec-
tors.
This means that the engine always receives the cor-
rect volume of fuel in all operating conditions, which
offers lower fuel consumption, minimal exhaust emis-
sions etc.
The control module checks and controls the unit injec-
tors so that the correct amount of fuel is injected into
each cylinder. It calculates and sets the injection an-
gle. The control is primarily performed using the speed
sensors and the combined sensor for boost pressure/
charge air temperature.
The control module affects the unit injectors via an
electronic signal to the unit injectors’ electromagnetic
fuel valve, which can open and close.
When the fuel valve is open, fuel flows past, through
the unit injectors’ holes and continuing out through the
fuel channel. Fuel is not sprayed into the cylinder in
this position.
When the fuel valve closes, pressure starts to build
from the unit injector’s mechanically operated pump
plunger. When sufficient pressure has developed, fuel
is injected into the cylinder via the unit injector’s injec-
tor section.
The fuel valve is re-opened and pressure in the unit
injector decreases at the same time as the fuel injec-
tion to the cylinder stops.
In order to determine when the fuel valve shall open or
close, the control module has access to signals from
sensors and switch contacts.
Calculating amount of fuel
The amount of fuel that is sprayed into a cylinder is
calculated by the control module. The calculation de-
termines the time that the fuel valve is closed (when
the fuel valve is closed fuel is sprayed into the cylin-
der). The parameters controlling injected amount of
fuel are:
• Rpm requested
• Engine protector functions
• Temperature
• Charge air pressure
Cylinder balancing
When idling, the control module can supply the cylin-
der with different amounts of fuel. This so the engine
will have a more even idle. At higher rpm, this problem
does not exist, and the cylinders receive the same
amount of fuel.
Altitude correction
The control module is equipped with an atmospheric
air pressure sensor and altitude correction function for
engines that operate at a high altitude. This function
limits amount of fuel depending on ambient air
pressure.The control module is equipped with an at-
mospheric air pressure sensor and altitude correction
function for engines that operate at a high altitude.
This is to prevent smoke, high exhaust temperature
and to protect the turbocharger from over-speeding.
Diagnostic function
The task of the diagnosis function is to detect and lo-
cate disturbances within the EMS 2 system, to pro-
tect the engine, and to provide information about prob-
lems that have developed.
If a malfunction is discovered, this is announced by
warning lamps, a flashing diagnostic lamp or in plain
language on the instrument panel, depending on the
equipment used. If a fault code is obtained as a flash-
ing code or in plain language, this is used for guidance
in any troubleshooting. Fault codes can also be read
by Volvo’s VODIA tool at authorized Volvo Penta
workshops.
In case of serious disturbances, the engine is shut
down completely or the control module reduces the
available power (depending on the application). Once
again, a fault code is set for guidance in any trouble-
shooting.

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