F10 523 N53B30 with a NOx problem

Today’s patient: F10, 523i with N53B30U0 engine.


For short indent – basic info regarding F series and N53 series engine.

For F series vehicles, N53 series engines are used in preLCI models in 3 different power versions with model names 523i, 525i and 530i. The most powerful version reaches 205kW/320Nm, ensured full torque in a wide range of RPM: already from 1300 RPM and full power in a range of 6000 .. 7000 RPM. This is the most powerful and responsible 6 cylinders 3-liter atmospheric engine in the BMW history.
N53 series engine uses Direct injection with Rail pressure 200 Bar, piezo injectors and the fuel is injected in the special Stratified charge mode. Thanks to Stratified charge, the fuel economy of around 15 .. 25% and a perfect responsibility of the engine is reached. Unfortunately, during Stratified charge, the engine emits an increased amount of NOx in the exhaust. To reduce it, the NOx system is used: a special catalytic converter, but the NOx content is measured by the NOx sensor.
Unfortunately, the lifetime of the NOx system is averagely around 150.000 km for the catalytic converter and 30 .. 50.000 km for the sensor.

If any of these elements is damaged, the engine stops to use Stratified charge and switched to the emergency mode. What are the consequences of such a situation?
a) fuel consumption increases for 15 .. 25%;
b) the fuel distribution in the cylinders is not optimal (in some cylinders the fuel mixture is rich, in some – lean) – the load of the exhaust system (CO catalytic converters) increases;
c) vibration in partial load mode appears;
d) incorrect thermal mode of the exhaust system – the performance and lifetime of CO catalytic converters is reduced;
e) problems to pass TI – increased CO/HC in the exhaust gasses;
f) uneven performance, shivering of the engine can appear, and it can not be solved y changing ignition coils, spark plugs and even injectors;
g) the engine doesn’t give full power, it is “clumsy”.

The largest problems are created by uneven fuel distribution between cylinders. Why this problem is so huge exactly at the moment when Stratified charge is turned off (prohibited)?
The answer – the peculiarity of the piezo injectors. These injectors are very fast – it is their plus and also a necessity to make Stratified charge possible but at the same time – they have a very wide parameter dispersion for short openings: idle, low load and average load mode. In low load modes, the performance of the injectors can differ for 3 .. 4 times! To solve this problem, DME creates a multi-dimensional adaptation map for each injector – measures each injector in all possible modes. Later these data (adaptations) are compensating the differences of injector parameters. Unfortunately, a wholesome measurement of parameters of injectors (including the leaking of the injector at the closed status and action time) is possible only in Stratified charge mode. If Stratified charge is turned off, the parameters of injectors are not measured completely – there are no data for the adaptation maps, and with time the situation will get more and more different from the ideal one (last measured data and the specification of the new injector, provided by the manufacturer) – problem increases with each driving session. If the cause of the problem is not known, many services recommend to replace all ignition coils, spark plugs, injectors. When it doesn’t help (or helps for a short moment) – to replace the high-pressure pump. When the replacing of the pump don’t help, the car is declared as irreparable.

Mileage of the current car: above 220.000 km, it has been used in our country for a long while. Unfortunately, the services which have been servicing this car didn’t consider it necessary to repair the NOx system. Accordingly – for a long time the NOx catalytic converter has not been serviced (regenerated and desulfated – cleaned of the sulfur) – it is definitely damaged.

Performing the diagnostics of the engine, the performance of all its systems is evaluated:
a) air supply: live data of air mass meter, pressure sensor;
b) fuel supply: performance of the high-pressure and low-pressure pumps – their pressures and the stability/jittering of the pressures in critical modes;
c) performance of the components of the exhaust system – voltages of wideband and narrowband probes, their conformity to the real situation;
d) performance quality of the VANOS system – jittering of the positions of camshafts;
e) performance of all additional systems: TEV, EGR, etc.
All previously mentioned systems are performing excellent, so I will not spend more time on them. Not taking into account this shortlisting, this is the main part of the diagnostics. Live data and functionality check of each system give all information regarding the performance of the engine. The error messages at the DME error message memory are recorded only in case of extreme/complete damage and the amount of the information is very small in case of more complicated problems.

The error message of the car contains the error message regarding NOx sensor readings, the engine doesn’t use Stratified charge.

Unfortunately, the sensor has to be replaced, there are no other solutions to restore the performance of the NOx system. It makes no sense to install an OEM sensor because the NOx catalytic converter is also damaged – DME will notice it very quickly, and Stratified charge will be disabled again. The only budget solution: installing the NOXEM emulator. NOXEM will inform DME, that the NOx catalytic converter is in a good technical condition, and DME will restore Stratified charge.

Said – done. At the picture – the service specialist is installing the NOXEM.


And here – after installing the NOXEM, the re-adaptation of the engine is done. At first: adaptations of the flywheel.


And in this image – they are already finished. Now it’s the turn of the fuel mixture adaptations.


Here already the engine is using Homogeneous lean mixture mode with Lambda around 1.5. Why not the Stratified charge? When starting the movement, some shivering of the engine can be felt – obviously, sometimes in some cylinder, some misfire appears. DME has noticed it and turned on the “lenient” mode. This problem we will have to solve with the next step.


Here – after a moment, the engine uses Stratified charge with Lambda around 3.00


Also, offset type LTFT – correct. So – with the airtightness of the inlet manifold everything is fine.

Everything looks perfect. When creating the adaptations, several tenths of parameters are checked (offset und multiplicative LTFT; adaptations of the injectors, Rough run data, etc). Only then, when all parameters are correct, the car is considered as repaired.


When checking the error message of the DME, we have to conclude:

my suspicions regarding noticed misfires have been confirmed – here, the error message regarding the uneven performance of the engine. Yes, many services recommend replacing the injectors, if they notice this error message. Why? Because at the description of the error message the fuel injection is mentioned. But not the injection is a problem – injection is mention to identify the performance mode (Stratified charge). If the service, when you repair your car, in this situation offers to replace the injectors – change the service! Otherwise, you can expect large and completely unjustified expenses!

Note: as you see, this error message has no analog in OBD – with any of “simple units” this error message will not even be visible. Just like other data, which are seen in this blog/entry. Not even worth to say – “universal” services with “universal” pseudodiagnostics equipment are completely helpless. The BMW dealer services and authorized services are almost at the same level – they are not allowed to use INPA (although it is developed by BMW engineers for “internal” use), nor EML327.


And, finally, returning to the misfiring problem – for this purpose the EML327 adapter is used. Here are the data:

Data indicate, that at the 6-th cylinder regularly are several tenths (at least 30 .. 50) misfire events in each driving session. Typically this problem is caused by the ignition coil and/or spark plug, rarer – the injector. Statistically: the injector is one to blame in this problem in 1 .. 2 cases of 100.
Unfortunately, also MSD87 (DME, which is used in F series vehicles) has the same cause of the damage of ignition coils, which I have noticed already in MSD80 – it is not fixed. Well, the owner of the F series vehicle will have to replace the ignition coils regularly…
In any case – the diagnostics have identified the problematic cylinder. So – the work will be with only 6-th cylinder, not at the level of “all injectors/coils/spark plugs have to be replaced”.


After a few days and replaced ignition coil:

As we see – all counters are 0. The engine works smoothly and all problems are gone.