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The OM 904 LA/ OM 924 LA (4-cylinder) and OM 906 LA /OM 926 LA (6-cylind er) engines are water-cooled four-stroke d ie-sel injection engines.
The cylinders are arranged in-line and have separate fuel-injection pumps (unit pump s) with a short high-pressure fuel-injection line to the multi-hole nozzle locat-ed centrally in relation to the comb ustion chamber. The unit pumps are mounted di-rectly on the crankcase. They are driven by the camshaft roller tappets. Each cylinder has two inlet valves and one exhaust valve.
The engin es are equipped with an exhaust gas turbocharger (sometimes with charge-pressure limiting) and intercooler as stand-ard. The engine can be optio nally equipped with an engine brake* (throttle and con-stantly-open thro ttle valves).
Thanks to its fully electronic control
sys-The control system comprises an en gine-resident control module, an engine control (MR) and an application-related vehicle control unit (FR) o r an adaptation module (ADM), all interconnected via the Control-ler Area Network (CAN).
Description of the engine
General
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The flame-start system is a cold-start aid for starting at low outside temperatures. It reduces the white smoke emission after the en gine is started. In ad dition, it reduc-es the strain on the starter motor and bat-teries by shortening the startup time.
Fuel can be ignited by a flame glow plug tegrated in the charge-air pipe from the in-tercooler. The fuel is supplied to the flame glow plug via a solenoid valve with a dosing jet.
Flame-start system
The flame-start system is primed after a preglow time (maximum 20 seconds) which is dependent on the outside temper-ature. After this time the flame-start sys-tem indicator lamp goes out.
Once the engine has started, the flame-start system is supplied with fuel by the en-gine's fuel delivery pump.
Flame-start system indicator lamp
The flame-start system is only operational if the engine is started within 30 seconds of the flame-start system indicator lamp going out.
Flame-start system*
Before commissioning
GeneralSee also the "Diesel fuels" section
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( see page 60) and "Coolant" section ( see page 63) for operation of the en-gine at low outside temperatures.
The grid heater is a cold-start aid for start-ing at low o utside temperatures. The chargeair is preheated by a heater strip in tegrated in the chargeair pip e from the in -tercooler. In additio n, it reduces the strain on the starter motor and battery by short-ening the startup time.
The white smoke limit is reduced by a run-on heating time of up to 180 secrun-onds after starting the engine.
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If the flame-start system indicator lamp does not go out after more than 20 sec-onds there is a malfunction in the flame-start system.
Grid heater*
General
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To increase braking power, the engine can be equipped with an engine brake valve on the exhaust gas turb ocharger in conjunc-tion with constan tly-open throttle valves on the cylinders.
While the exhaust gas back pressure from the engine brake valve is used to increase the braking power, the constantly-open throttle valves cause a pressure reduction in the working cycle (3rd cycle), while com-pression (2nd cycle) is practically unaffect-ed.
The constantly-open throttle valves are small valves in the cylind er head and locat-ed on the side opposite the exhaust valve.
When open, they form a connection from the combustion chamber to the exhaust port.
Constantly-open throttle valves on a 4-cylin-der engine
When the en gine brake* is applied , the constantly-op en throttle valves are pneu-matically pressurised on the 4-cylinder en-gine and hydraulically pressurised on the 6-cylind er engine. This opens the valves.
At the same time, the engine b rake valve on the exhaust gas turbocharger is closed.
The constantly-open throttle valves are not controlled at lower engine speeds (900/
1,300 rpm) or at temperatures belo w 40 °C. When the power unit is being used, these limitations must be taken into ac-count under braking conditions.
Exhaust brake/ constantly-open throttle valve*
Before commissioning
General3
The engine brake* is controlled b y the drive co ntrol un it ( page 31) or the ADM.
The engine brake* is always disab led be-low 900 rpm to prevent the engine from stalling. The engine brake* is also auto-matically deactivated if the position sensor is triggered (e.g. if the accelerator pedal is depressed).
The engine has a fully electro nic control system, which, in addition to the engine and related sensors, also comprises:
an engine control unit, and
a drive control unit and/ or other vehi-cle-specific control units or ADM.
Both are interconnected via a CAN (Con-troller Area Network) line which exchan ges all the necessary d ata / information.
The engine control monitors itself as well as the engine. A safety and emergency run -ning program is selected automatically de-pending on the malfunctions /failures occurring ( page 39).
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In emergency running mode (constant engine sp eed), the engin e brake* can only be activated in o verrun mode at a higher engine speed. The engine brake* is automatically d isabled again once the constant engine speed has been reached .
Telligent® engine system
General
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Engine control unit (engine-resident) The engine control unit is located on the left-hand side of the engine.
Engine control unit
The engine control unit pro cesses data coming from the drive control unit or the ADM, such as the position of the setpoin t value sensor (accelerator pedal), the en-gine brake* or enen-gine start/ sto p, etc.
This data is evaluated along with data from the sensors on the engine, such as those for:
charge-air pressure and temperature
coolant temperature
fuel temperature
oil pressure
These parameters are compared with the characteristic maps and graphs stored in the engine contro l unit.
Start, duration and amount of injection are calculated from the graphs and the unit pumps are controlled accordingly via the
solenoid valves. Control unit type plate
1 Data record 2 Certification no.
3 Engine plate 4 Equipment code
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All the information on the control unit type p late is required to obtain a re-placement engine control unit.
The type plate is located on the engin e control unit in the upper right-hand cor-ner.
Before commissioning
General3
FR (drive control) unit or ADM (appliance-resident)
The engine can be adapted to meet the various application-sp ecific requirements by means of the FR (drive control) unit or adaptation module (ADM).
Drive control unit
The FR (drive co ntrol) unit or the ADM unit stores data for specific applications, such as idling speed, maximum working speed and speed limitation.
The FR (drive control) unit and the ADM re-ceive data from the
operator (position of setpoint value sensor, engine start/ stop)
engine brake switch*
other systems (e.g. traction control)
engine control unit (e.g. oil pressure and coolant temperature)
From this data, the instructions for the MR (engine control) unit are computed and transmitted to it via the CAN line.
The drive control unit and the ADM control various d isplays, e.g. the electronics warn -ing lamp, the engine brake* and the con-stantly-open throttle valves*.
General
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If the Telligent® engine system detects a fault, this is stored as a fault cod e in the control units and can be read using the ap-prop riate diagnostic equipment (STAR DIAGNOSIS o r Minid iag 2).
In addition, the electronics warning lamp is switched on.
Diagnostic socket
Organisationa l measures
The Operating Instructions and Mainte-nance Booklet must b e given to the per-sonnel resp onsible for operating the engine or carrying out work on the en gine, and should be kept in an easily accessible place where the engine is used.
Personnel must be instructed in how to work on the engine using these Operating Instructions. In particular, the safety notes must be explained. This is especially im-portant for personnel who only work on the engine occasionally.
In addition to these Op erating Instructions, the country-specific legal and all other binding regulations for accident prevention and protection of the environmen t must be observed.
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The DaimlerChrysler diagnostic testers can be connected to the equipment-resident, 14-pin diagnostic socket.
Both the malfunction memory and the stored engine data can be read with
this equip ment. Risk of accident and injury
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Before operating the engine, please read these Operating Instruc tions and other rele-vant doc umentation, such as the operating instructions for the vehic le or the machine the engine is installed in.
You c ould otherwise fail to recognise dan-gers and could injure yourself or others.