About today’s topic, I have received quite many questions.
Uneven performance of the engine – can the air mass meter be one to blame? Does it have to be cleaned?
Here, for example, a video, how one “specialist” cleans air mass meter:
At first, some facts regarding N43/N53 air mass meter:
- air mass meter is a thin wire, which is not supposed to be touched to avoid its damage;
- this wire is cleaned automatically every time when the engine is turned off (it’s temporarily heated to 800 oC);
- any cleaning agents (aggressive chemicals) can do irreversible damages (and also they do);
- if these chemicals will get in the electronics management unit of air meter, it will be irreversibly damaged!
- “cleaning” of air mass meter is the main cause, why also the sensor of inflow air temperature (its wires are damaged with aggressive chemicals of cleaning agents) is damaged.
A little bit about data processing of air mass meter.
For modern engines, the air mass meter is used in “different” way as in first M series engines. If for first M series engines (M10/20/30) the amount of fuel to injected was calculated, using online data of air mass meter, then for N series engines this calculation is done in a different way. The amount of fuel is calculated in accordance with the mathematical model of the engine – theoretical calculation, which is affected by data of the sensors. A mathematical model is created by BMW engineers, researching the performance of the engine in a wide variety of different conditions and modes, this model is affected by many measured (true, characteristic to a current engine) parameters: the opening of the throttle, data of sensor of inlet manifold pressure, etc.). Air mass meter is only one of sensors, whose data are taken into account. Even more – data or air mass meter can be checked all the time (and also are checked), using data of other sensors. Additionally, in case of swift changes of the engine mode (for example, swift pressing of the accelerator pedal), data are taken only from mathematical model (virtual calculation, which is obtained, “learning” from previously collected data), not sensors (it is done to ensure, that reaction to pressing the accelerator pedal will be momentous, not delayed, awaiting when stable and correct data from sensors would be received – for example, while the air pressure in the inlet manifold becomes even). The mathematical model knows, how to “predict” behavior of the engine, not waiting for the data from sensors. In turn, in case of even mode, a continuous reciprocal check of all data (for example, throttle, air mass meter, air, and fuel pressure sensors, data of Lambda probes, etc.) and creation of sensor adaptations are performed. Accordingly, if data of any sensor are different from ideal, the adaptation maps will correct the data (eliminating technological differences from ideal).
This cleaning of air mass meter has come from times of M10/M20/M30 engines when air mass meter was a mechanical element. Time has gone forward, and the anemometric type air mass meters of new engines have nothing in common with “old” type air mass meters, in which the air flow moved mechanical shutter, which, instead, was turning potentiometer.
There is no need to clean the air mass meter! Such “cleaning” can only damage it! In case of a defect of air mass meter (its damage or inappropriate data) definitely, the corresponding error will be recorded! The air mass meter will not be the one to blame if the engine performs unevenly, but there are no error messages regarding air mass meter.
Even, if we theoretically assume, that the air mass meter data suddenly started to differ from correct ones, DME knows, how wide is the opening of the throttle, sees the pressure in the inlet manifold, sees the true proportion of the fuel mixture – inappropriate data will be spotted immediately. Accordingly – the air mass meter will be “locked out” from a number of sensors, from which the data are taken, the engine will start to perform in one of many emergency modes – without using this sensor. Moreover, as I already mentioned before, the data from air mass meter are used to manage slow processes, from example, to calculate the relative amount of oxygen in the air and its absolute pressure (taking into account changes of air, for example, when driving in mountains – in conditions of low air pressure or in case of high CO content). But – these are slow adaptation processes, which can not cause swift (several seconds or even shorter) unevenness in the performance of the engine.
If you are worried about the performance of indications of air mass meter and temperature sensor of inlet air, you can check corresponding data:
../F5/F2/F6, where you can see the used amount of air and calculated pressure of the surrounding environment;
../F5/F2/F3, where you can see the data of the inlet air temperature sensor.
In the end – a small comment regarding inlet air temperature. MSV/MSD engine management systems are comparing the data of outside temperature sensor (which is located in the front of the car) with data of the sensor, who measures the temperature of the air, which floes in the engine. Due to this cause, an abnormal performance of the engine can be spotted (“slipping” of the fuel adaptations and similar), if the outside temperature sensor is damaged.