Turbocharger: Testing and Inspection
Exhaust Turbocharger Check On The N63/N74 Engine
1. Visual inspection
Visual inspection of all lines, hoses, connections and cables should serve to provide quick discovery of obvious faults.
2. Check blow-off valve
If a blow-off valve does not close, i.e. is stuck open, sufficient charging pressure can normally not be built up. The blow-off valves are electrically activated. The piston of a blow-off valve is not pre-tensioned with a spring but rather moved by air pressure. Through current supply, the blow-off valve is closed against this air pressure. A blow-off valve which is jammed open is possibly indicated by whistling noises. A blow-off valve which is jammed closed is possibly indicated by noises (fluttering) when the foot is taken off the accelerator pedal.
3. Active diagnosis
The active diagnosis is a DME function. The function runs within a temperature window from 80-105°C. The function generates an artificial load. This facilitates a diagnosis only in the charged mode. However the engine generates heat during this and the electric fan is therefore activated. This component reacts slowly, therefore the function may possibly abort near the two limits. The function increases the engine speed to generate load. The DME then alternatingly activates the wastegate of the exhaust turbocharger. During this, the pressure histories are monitored by the pressure sensors. According to the pressure histories of the individual exhaust turbochargers, the DME evaluates the behavior of the charging system. At the end of the function, a message about the status of the charging is displayed. If the charging system is found to be OK and there is only one customer complaint an additional troubleshooting is unnecessary.
4. Check the exhaust flap
The function of the exhaust flap affects the charging at different operating points through the generated counterpressure in the exhaust system. A continuously closed exhaust flap can lead to charging faults. The exhaust flap is activated by vacuum. A vacuum line which has been pulled off can suck in particles such as dust, salt water etc. and transport these to the vacuum pump. This can cause damage to the vacuum pump.
5. Check the electropneumatic pressure converters (=EPDW)
The electropneumatic pressure converters are activated individually so that -450hPa is routed to the wastegate. The adjustment of the wastegate can be partially observed from above. During the activation, the vacuum can be checked using a manometer, if necessary. If the vacuum line is disconnected, a delay of the pressure build up is to be observed.
6. Check the differentiated air intake system for leaks with auxiliary diagnosis equipment
For discovering leaks, the use of auxiliary diagnosis equipment 81 29 0 426 464 is mandatory. Please also observe the repair instructions RA 11 61 730. The seal plugs must seal the differentiated air intake system airtight.- No leaks are to be found through fizzing noise.- Larger leaks are normally visible or the pressure cannot be built up using the auxiliary diagnosis equipment.
7. Check wastegate and blow-off valve
If a wastegate or a blow-off valve does not close, i.e. is stuck open, sufficient charging pressure cannot normally be built up. Wastegates that are stuck closed normally generate overcharge faults; blowoff valves are normally indicated by noise (fluttering). The wastegates are closed through vacuum. For this, -300hPa must be sufficient.
If the wastegates first close at low pressures, they are stiff. For additional wear, the flaps no longer close completely or jam in their seat. The blow-off valves are supplied with vacuum by means of an electropneumatic pressure converter and thus opened.
8. Check catalytic converter and turbo module
Catalytic converters can influence the charging through modified exhaust gas counterpressure. This is normally detectable through melting or combustion in the honeycomb structure. Annealing colors on the outside of the catalytic converter can also indicate this type of damage. Damages to the exhaust turbocharger are normally visible through, e.g. broken turbine wheel, stuck turbine shaft or oil leakage. For oil leakage, the catalytic converter must absolutely be checked for subsequent damage.