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Description of operation, engine management system

Description of operation, engine management system


Starting fuel quantity calculation

The starting fuel quantity is the amount of fuel allowed when starting the engine. The function is activated when starting the engine is possible and is terminated at engine speeds above 750 rpm.

The fuel quantity is calculated using the following sub-functions:

Base value

A base value is retrieved where the starting engine speed and engine coolant temperature are the input values. The value is corrected in the starting quantity correction once the engine starts to rotate.

Starting quantity correction

The starting quantity correction is calculated from the current engine speed. The max. correction is 5 mg/combustion and it decreases with the engine speed (0 mg/combustion at 750 rpm).

Starting quantity enrichment

Starting quantity enrichment ensures problem-free starting at all temperatures. Enrichment is calculated from the pump temperature, engine speed and the time it takes for the engine to start. Different parameters are selected for cold starting enrichment depending on whether the pump temperature is above or below 10°C.

The results of these calculations are totalled and form the total starting fuel quantity.

The starting fuel quantity can be decreased or increased by 5 mg/combustion with the diagnostic tool.

Limit quantities


The sub-functions under limit quantities calculate the largest permitted injection quantity in mg/combustion for the current operating conditions. The calculated limit quantity is used to limit the requested quantity from the pedal position sensor and the cruise control if it should be necessary. The calculation is performed at fixed time cycles, independent of the engine speed.


1. The result of the calculation in the smoke limitation and torque limitation sub-functions are compared and the function that gives the lowest injection quantity is the value that is carried forward.

Example: The result of the smoke limitation is 40 mg/combustion and the result of the torque limitation is 60 mg/combustion. This means that the value from the smoke limitation (40 mg/combustion) is carried forward.

2. The result of the temperature compensation is added to the result of the calculation above.

Example: 40 mg/combustion + 5 mg/combustion = 45 mg/combustion.

3. This value is compared to the value from the boil protection and the lowest value is carried on as the limit quantity unless there is a system error.


Example: 45 mg/combustion is compared with the boil protection value 60 mg/combustion. This means that 45 mg/combustion is carried forward as the limit quantity.

4. However, if there is a system fault, 45 mg/combustion is compared with the limit quantity on system fault (rpm dependent, max. 30 mg/combustion), and the lowest value is carried forward as the limit quantity.


Smoke limitation

There is a smoke limitation function to prevent the formation of large amounts of smoke.

Smoke limitation is calculated using engine speed, absolute pressure sensor and intake air mass in mg/combustion. The function is designed so that the fuel quantity in mg/combustion always contains sufficient air mass in mg/combustion to prevent large amounts of smoke developing.

If this is not the case, smoke limitation is activated and the fuel quantity is reduced to a level at which the available air mass is sufficient to burn the fuel without the formation of large amounts of smoke. This takes place when driving at high altitudes for example, as the proportion of oxygen in the air decreases at higher altitudes.


Torque limitation

In order to adapt the engine torque, a torque limitation quantity is obtained based on the engine speed. This is a pre-programmed value in relation to the requested value from the throttle potentiometers.


Temperature compensation

A cold engine requires enrichment to ensure smooth running.

If, on the other hand, the engine is on the verge of overheating, this function will engage to reduce the fuel quantity.

Information for this control comes from:


• Oil temperature sensor

• Coolant temperature sensor

• Fuel temperature sensor



Quantity compensation

Depending on variations in the diesel fuel, it may be of different densities. A lower density of the fuel will reduce the power of the engine and a higher density will make the engine smoke more. The quantity compensation function is used to compensate for variation.

The limits are quantity compensated by multiplying them by a value between 0.95 and 1.05 mg/combustion.

The quantity compensation can be adjusted 5% with the diagnostic tool.


Boil protection

The engine will engage boiling protection if the coolant temperature, fuel temperature or engine oil temperature become too high and this will reduce the permitted fuel quantity.

The boiling protection function reduces the fuel quantity depending on the coolant temperature and vehicle speed, fuel temperature or engine oil temperature and vehicle speed. The two limitation values giving the smallest injection quantity are used.

The reduction is considerable, which means that it is very noticeable to the driver. This is so that the engine is given the opportunity to stabilise its temperature and avoid damage. The AC function is disengaged.

If the engine has been on the verge of boiling, a diagnostic trouble code will be generated that can be read using the diagnostic tool. The DTC is cleared after 60 starts with a fault-free system or with the diagnostic tool.


Requested quantity from accelerator position sensor

The requested torque is sent from the pedal position sensor to the PSG 16 control module. The control module adjusts the amount of fuel/combustion so that it agrees with the requested torque.

The pedal position sensor value is filtered when there is an increase or decrease in throttle.




Compensation for A/C compressor operation

This function is activated when the A/C compressor starts, compensating for the extra torque that the A/C compressor takes from the engine with an extra fuel quantity/combustion.

The compensation quantity from the "compensation A/C compressor operation" function is added to the value "requested quantity from pedal position sensor". The compensation fuel quantity depends on the pressure in the A/C system and is approx. 2-3 mg/combustion.

PSG 16 read the A/C pressure on the bus.


Control module calculations

The result from the calculations performed by the engine control module is sent on the P-bus and is read by the diesel pump control module, which processes the information as stated in the diesel pump description.