Turbocharger: Testing and Inspection
Turbocharger Check On The N54 Engine
1. Visual inspections
Visual inspections of all lines, hoses, connections and cables are intended to help locate obvious defects quickly.
2. Active diagnosis of the turbochargers
The active diagnosis is a DME function. The function runs within of a temperature window of 80 - 95 °C .
To decouple the two turbochargers, the connecting line (low pressure hose) between the two electropneumatic pressure converters (= EPDWs) must be disconnected (air-tight) by means of a special tool (see illustration). The function generates an artificial load. Only then is diagnosis in the charged mode possible. However, the engine generates a great amount of heat here, which is why the coolant pump and electric fan are activated. These components react sluggishly, which is why the function possibly aborts in the vicinity of the two limits. The function increases the speed to generate a load. Subsequently, the DME alternately activates the wastegates of the turbochargers. In the process, the courses of pressure are monitored by the pressure sensors. In accordance with the courses of pressure of the two decoupled turbochargers, the DME evaluates the behavior of the turbocharger system.
At the end of the function, a message regarding the status of the charge is displayed.
If the turbocharger system is judged to be "OK" and there is only a customer complaint, further troubleshooting is unnecessary.
3. Check the exhaust flap
The back pressure generated in the exhaust system means that the function of the exhaust flap affects the charge in various operating points. A permanently closed exhaust flap can lead to charge faults.
The exhaust flap is vacuum-controlled. A disconnected vacuum hose can draw in particles (dust, salt water, etc.) and deliver then up to the vacuum pump. This can damage the vacuum pump.
4. Check the electropneumatic pressure converters (= EPDW)
The electropneumatic pressure converters are activated individual in such a way that -450 hPa is fed to the wastegates. Some of the adjustment of the wastegates can be observed from above, but it is better to observe from below (underbody panelling removed).
During activation, if necessary, the partial vacuum can be checked using a pressure gauge. If the vacuum hose is disconnected, there will be a delay in the vacuum build-up.
5. Check the intake system for leak-tightness with the diagnosis device
To find leaks, be sure to use diagnosis device 81 29 0 426 464. In this context, consult repair instruction RA 11 61 730. The seal plugs must close off the intake system and make it air-tight. - Small leaks can be found because of hissing noises. - As a rule, larger leaks are visible or the pressure cannot be built up with the diagnosis device.
6. Check the wastegate and blow off valve
If a wastegate or blow off valve does not close, i.e. jams open, it is usually not possible to build up adequate charge-air pressure. Wastegates that jam closed might generate overload fault; blow off valves might produce noises (vibrating).
The wastegates are closed by partial vacuum. -300 hPa must be sufficient for this. If the wastegates are only closed at lower pressures, they are difficult to move. With further wear, the flaps no longer close completely or jam in their seats.
The blow off valves are force-opened by partial vacuum from the intake pipe after the throttle valve.
7. Check the catalytic converter and turbo module
Catalytic converters can influence the charge due to changed exhaust-gas back-pressure. As a rule, this can be seen by traces of melting or burns in the honeycomb structure. Smeared colors on the outside of the catalytic converter can also indicate damage of this nature.
As a rule, damage to the turbocharger is visible, e.g. broken turbine wheel, jamming turbine wheel shaft or oil spillage. In the case of oil spillage, the catalytic converter must be checked for consequential damage without fail.