Air Mass System Test For Diesel Engines

Air Mass System Test For Diesel Engines

Air mass system
The air mass system consists of several component groups that ensure the optimum fresh air supply to the engine at every operating point. Malfunctions in these component groups cause a variety of disturbances in driving operation, for example lack of power, black smoke, etc.

The air mass system test runs an overall check of the air mass system and thus allows clear pinpointing of the cause of the fault to the defective component group(s).

Component groups of the air mass system
The air mass system consists of:
- Charging pressure sensor
- Intake air temperature sensor
- Charge air temperature sensor
- Air mass meter
- The exhaust-gas recirculation (EGR) actuator comprises the EGR valve with position sensor, pressure converter, pneumatic and electrical activation of the pressure converter (N47 EURO4)
- Electrical exhaust-gas recirculation actuator, includes the EGR valve with electrical actuator (N47 EURO5, EURO6, N57)
- Electric exhaust-gas recirculation actuator (N57)
- Charging pressure actuator, comprises turbocharger with adjustment, electrical activation of the charging pressure actuator
- Swirl flaps with electrical actuator (not on N47D20u0 and N47C)
- Air filter, air hoses, pipes, charge air cooler, exhaust system, etc.

Test sequence
1. The charging pressure sensor is checked for indication of plausible values.
2. The intake air temperature sensor and charge-air temperature sensor are checked for signal plausibility
3. The air mass meter is checked at cutoff speed and idling by a comparison between measured and theoretically calculated air mass (exact description, see procedure and function test instructions "Mass air flow meter").
At the same time, there is a check as to whether the system builds up the charging pressure quickly enough and to a high enough level.
4. Functional check of the exhaust-gas recirculation actuator and the charging pressure actuator/turbocharger by means of the following automatic test procedure:
- Activation of the charging pressure actuator at minimum pulse duty factor (TV)
- Gradual opening of the exhaust-gas recirculation actuator, measurement of the air-mass change
- Closure of the exhaust-gas recirculation actuator
- Activation of the charging pressure actuator at maximum duty cycle
- Gradual opening of the exhaust-gas recirculation actuator, measurement of the air-mass change
The idling speed is automatically increased for this test.
5. The measured changes in air mass flow are automatically analyzed. They are compared with one another in such a way that conclusions can be drawn as to the function of the exhaust-gas recirculation actuator, the charging pressure actuator and the turbocharger.

Evaluation of the test
The program automatically evaluates the test and specifies the procedure for any further troubleshooting.

NOTE: If incorrect measured values are specified for the air mass meter and at the same time for another component group, the fault on the mass air flow meter is likely to be a secondary fault. For this reason, fault elimination must be started at the other component group. In cases of doubt, the function of the throttle valve and swirl flaps should be checked.

The air mass system test must then be repeated in order to check the mass air flow sensor once again.

Evaluated and displayed measured values
The measured charge-air values are also displayed.

Influence of the swirl flaps
A malfunction on the part of the swirl flaps has only a slight effect on the air mass system test.

However, a malfunction of the swirl flaps can lead to fault entries with regard to plausibility of the air mass.

When driving, a malfunction of the swirl flaps has the following effects:
- Swirl flaps stick in closed position: lack of power at high engine speeds
- Swirl flaps stick in closed position: deterioration of exhaust emissions

Requirements for the air mass system test
In order to ensure that the air mass system test delivers a meaningful result, the following requirements must be met:
- The engine must be at operating temperature
- All additional loads, e.g. air conditioning system or seat heating, must be switched off
- No electrical faults in the following systems may be stored in the DDE fault memory:
- Air mass meter
- Exhaust-gas recirculation actuator
- Charging pressure actuator
- Charging pressure sensor
- Intake air temperature sensor
- Charge air temperature sensor
- Ambient pressure sensor
- Throttle valve
- Swirl flaps
- The air intake duct and air filter must be OK
- Diesel particle filter must not be clogged
- Regeneration of the diesel particle filter may be active or requested
- The throttle valve and swirl flaps must be functional