Rough run. Trim errors. Hidden cause

The most woe of N43/N53 series engines: uneven operation – is well known to all interested, enthusiasts and repairers.

Yes, sometimes spark plugs, ignition coils and injectors are ones to blame. But one tricky cause is hiding, and nobody mentions of it. What could it be?

 

But now – step by step about everything.

 

The chart describes the relation between NOx system problems and increased fuel consumption, rough run, shivering, fuel trim errors.

N43 and N53 series engines are the most advanced everyday use engines in BMW history. They are No.1 in all aspects: they are the most complicated, but also – the most responsible, with the largest power (100 hp/1 liter) and an excellent torque curve.

These engines can work in 3 completely different fuel injection modes:

  • Homogeneous mode (in this mode all “regular” petrol engines are working);
  • Homogeneous lean mode;
  • Stratified charge fuel injection.

Last two fuel injection modes in the BMW engine family are used only for N43 and N53 series engines. These injection modes allow to save fuel (15 .. 25%) and provides an excellent responsibility of the engine. Unfortunately, while working in these specific modes, the engines are emitting an increased amount of NOx content in the exhaust. For the engine to correspond to Euro4/Euro5 ecology requirements, they are equipped with a NOx catalytic converter, which reduces amount of the NOx (emitted in the environment), and with NOx sensor, which continuously measures the amount of NOx in the exhaust and follows up the performance and well-being of the NOx catalytic converter.

If at least one of the NOx system elements is damaged, the engine management disables Homogeneous lean and Stratified charge modes. The engine switches to a “simple” (actually – emergency) – Homogeneous mode, because in it the NOx content in the exhaust is low enough even without using the NOx system. Fuel consumption increases. But, if the Stratified charge mode is turned off, the owner of the car can expect a series of “pleasant” symptoms:

  • the idle of the engine becomes uneven – persistent vibration can be felt;
  • when driving – vibration can be felt; the feeling, that some of the cylinders are not working properly, is not leaving;
  • quite often serious problems with a cold start of the engine appear – the engine shivers, shakes;
  • in the DME error message memory the error messages regarding fuel mixture, misfires, Lambda probe trims appear;
  • typically – in KOMBI the EML (Check Engine) lights up;
  • very often – also the error messages regarding reduced efficiency of the CO catalytic converter are stored;
  • the engine doesn’t give full power, it is clumsy and unresponsive;
  • if the vehicle is equipped with an automatic gearbox, it is switching very awkward;
  • the engine tends to shiver even switching on and off AC; switching on and off any powerful consumer (blower, heating of rear window or seats, etc.).

All these symptoms stubbornly don’t disappear after replacing all possible culprits, for example: ignition coils, spark plugs, injectors.

 

Cause of all these symptoms – problems with the NOx system!

 

Why exactly the NOx system causes this series of problems?

A stratified charge is the main fuel injection mode of these complicated engines. Exactly due to this mode, these engines have a list of fundamental innovations:

  • this is Direct Injection engine with a Rail pressure 150 .. 200 Bar;
  • for fuel injection, this engine uses piezo injectors.

Piezo injectors are very fast – this is a necessity, which allows executing the injection of Stratified charge and very economical performance. Unfortunately, these injectors have an Achilles heel – they week spot is a wide parameter dispersion in idle, low load and middle load modes. For example, in idle their parameters (amount of injected fuel) can differ for 3 .. 4 times!

To solve this problem of parameter difference, DME regularly performs measurements of the each injector for each driving conditions (creates multi-dimensional adaptations maps for each injector), and, when the data regarding each injector are known, compensates the differences of their parameters. DME is very smart, if, for example, can even detect, if the rich fuel mixture in some of cylinders is due to leaking of the injector in a closed state, or the injector is slightly late with the closing!

But all most advanced measurements are possible only in Stratified charge mode. If this mode (due to problems of the NOx system) is prohibited – there are no necessary injector measurements, there are no data regarding differences of their parameters, the compensation of the parameter difference is not possible.

If Stratified charge is prohibited, with each driving sessions the existing situation gets more and more different from an ideal one (the last injector measurements and data, which are given by the manufacturer). With each driving session:

  • the fuel mixture disbalance between cylinders increases – in several cylinders the fuel mixture is rich, at the same time in some – lean: due to this, vibrations and misfires appear;
  • DME can not predict the behavior of the engine in conditions of variable loads; due to this – vibrations appear when some consumer is switched on or off;
  • DME can not create the long-term fuel adaptation maps (LTFT) – for this reason, the problems with a cold start appear, also the shivering of the engine on the run;
  • yes, DME sees, that the fuel mixture is not correct, so it records the error messages regarding it, but is not able to fix the situation because there are no data regarding injectors and their behavior;
  • due to this incorrect fuel mixture, the load of the CO catalytic converter increases, they are overloaded – so there are the error messages regarding them too;
  • due to incorrect fuel mixture, the car has problems to pas the TI: when the exhaust gasses are checked, an increased amount of CO/HC is detected.

Unfortunately, even the replacing of the injectors don’t solve this problem – after a short moment, all previously mentioned symptoms and problems return!

 

Only restoring of the working capacity of the NOx system and restoring of the Stratified charge fundamentally will prevent the problems, mentioned before.

 

The NOx system has to be maintained not only by this reason, that it is one of the conditions for driving to be comfortable and economical. If the fuel mixture is not optimal, following problems appear:

  • the workload of the CO catalytic converters significantly increases, they get damaged quickly. Unfortunately, these catalytic converters are critically necessary for the car to pass the TI (for the exhaust gasses to fit in the norm);
  • if the car is shivering (misfire problem), the unburned fuel is thrown in the exhaust and explodes there – both CO catalytic converters and Lambda probes are getting damaged.

CO catalytic converters for these cars are expensive, there are no alternative products. If you want to save yourself from bill of several thousands of EUR or at least “zoom-out” the problems with CO catalytic converters – repair the NOx system immediately!

 

NOx system problems. Affected vehicles. 538 vehicles inspected. Data: MSD80 history memory log.

Disclaimer: data represents situation monitored in current area and driving conditions and may vary into other areas/driving conditions and may not represent data monitored by BMW AG. For illustrative purposes only.

BMW N53 NOx system problems graph

Properly working NOx system is a critical requirement. Restoring the Stratified charge (which fundamentally solves the problem) for N43/N53 series engines is not possible in  “cheap & easy” way. In addition:

  1. you can’t downgrade the engine to “older” version (version without Stratified charge) by reprogramming because for this engine the Stratified charge mode is a basic fuel injection mode, which is not possible without functioning of NOx system;
  2. erasing of corresponding error message codes from error message map also does not helps. Error messages don’t appear anymore, but all problems remain;
  3. disconnecting the NOx sensor don’t help;
  4. the simple (by programming) simulation of NOx sensor is not possible (it’s connected with loCAN and does not receive necessary data from dCAN);
  5. if the insufficient efficiency of NOx catalytic converter is determined (30E9 error message appears), “cheating” with the registration of “new” NOx catalytic converter also doesn’t help – MSD80 realizes (very quickly), that the converter’s performance is inadequate and renews active status of 30E9.

 

NOXEM – solution for NOx system problems: NOx catalytic converter and NOx sensor.

Detailed information about NOXEM 129

Detailed information about NOXEM 130

 

P.S. Why the adaptations are critically important to correct fuel mixture? You can read more about this on adaptation and compensation topic, but shortly:

each component has it’s technological tolerance, usually not less than +/- 5 .. 10%. Accordingly, high-pressure fuel pump, injector, VANOS solenoids, sensors, etc. have such tolerances. Such inaccuracy (which are very common already to new spare parts, can overcome this tolerance, when parts wear out) in the worst case can sum in more than defined (allowed by STFT) 10 .. 12%. Exactly by this reason adaptations are used – this long-term additional correction (stored in engine management controller between driving sessions) significantly wider permissible tolerance of mechanical and electrical components.

 

And now the list of error messages for problem described above:

2AEC Nitrogen Oxide Sensor Self Diagnostics

2AF0; 2B05 nitric oxide sensor, heating

2AF2; 2B06; 2B09 nitric oxide sensor, Lambda linear

2AF4; 2B07; 2B0A NOx sensor, electrical

2AF6; 2AFB; 2B0B nitric oxide sensor, Lambda binary

2AF9 nox sensor, nox signal: coast mode check

2EAE NOx sensor message missing (timeout)

30D6 nitric oxide sensor, plausibility

30D8 NOx sensor, Sensor damaged

30DA NOx sensor, heating time

30DC nitric oxide senor, heating

30DE NOx sensor – Lambdaprobe before catalyst, Korrelation

30E0 NOx sensor, Offset

30E2 nitric oxide sensor, thrust test

30E4 nitric oxide sensor, aging

30E6 nitric oxide sensor, dynamics

30EA nitric oxide catalytic converter, sulphurized

30E9 nitric oxide catalytic converter, aging

 

Related entries:

Stratified charge performance check

Components of NOx system

STFT and LTFT

How I perform adaptations

Replacing NOx sensor

NOx catalytic converter regeneration and desulfation