Uneven run. Regeneration

In this entry – about quite a specific problem, which is typical only for N43/N53.


Symptoms of the problem: unevenness of the engine, separate misfires, which can appear periodically (interval – several tens of seconds .. several minutes). Symptoms can be spotted:

  • for partly warm (more expressive) and warm engine;
  • in a range of average load, when driving evenly.

This problem is characteristic, when the engine works in Stratified charge (in case of larger load – in Homogeneous lean mode), but disappears by load above 60% of inquired torque (when the engine switches to Homogeneous mode). Problem is more pronounced for vehicles with a manual gearbox. For vehicles with automatic transmission, in lower speeds, the torque converter of the automatic transmission is not locked, which makes this unevenness of the engine “softer”.


These misfires don’t disappear even after replacing the injectors, ignition coils, and spark plugs. Also, preventive maintenance of other systems doesn’t help. No need to add, that all fuel LTFT, individual adaptations of cylinders are correct, all other systems (VANOS and others), according to diagnostics data – perform perfectly.

One more peculiarity in case of this problem – misfire counters are close to 0, not taking in account misfires, which can be clearly felt.


Cause of the problem – incorrect fuel mixture in short-term, while the engine performs regeneration of NOx catalytic converter, as well as when swiftly switching between work modes. As we know, regeneration of NOx catalytic converter is performed after each 10 .. 60 seconds (depending on technical condition and load of NOx catalytic converter), if the engine works in Homogeneous lean or Stratified charge mode. During regeneration sessions, the misfire detection functionality is turned off, for this reason, misfire counters will not indicate any problems in case of this defect.


This problem is typical for earlier software releases of MSD80/81. For later software releases, the regeneration of NOx catalytic converter (also algorithms of switching of other engine modes – Homogeneous, Homogeneous lean, Stratified charge) is updated. Undoubtedly – engineers of BMW AG at the time have indicated and eliminated the problem.

Note: last (newest) MSD80/81 software releases are dated with Year 2010/2011.


In the images below I will compare, how does it “look alike” the regeneration of NOx catalytic converter for earlier releases and after elimination of the problem.

Earlier releases: on the left; after the elimination of the problem: on the right.

As we see, in the upgraded version the switching between modes is performed much slower and evener. At first evenly (during 1 .. 2 seconds)  Lambda is reduced to 1.00, then follows long enough (0.5 .. 1.0 second) pause in Homogeneous mode, only then – the regeneration session for each bank. After that – again pause on Homogeneous mode, very smooth restoring of Lambda, when returning to Homogeneous lean or Stratified charge mode. Regeneration time of each bank has not changed (it’s around 1 second long for each bank), but the total time of all phase of regeneration is increased from 3 to around 5 .. 6 seconds.

It’s only a logical question – why the BMW AG already initially didn’t order such “correct” algorithms? One of the explanations could be, that such switching increases fuel consumption.

In addition to these changes, in later releases one more correction have been done – the minimal time between regenerations of NOx catalytic converter was reduced from 15 to 10 seconds. Obviously, the BMW AG engineers noticed, that the real lifespan and efficiency of NOx catalytic converter are worst than initially planned, the error messages 30EA and 30E9 appear often.

Probably, one to blame – increased amount of sulfur in the fuel, possibly – the profile of driving. But this reduction of this minimal interval (between regeneration phases) together with prolonging the switching time means, that average car, which has driven around 50’000 km and more, regenerations would take almost half of time!

It’s clear, that during regenerations the fuel consumption is higher – the engine switches to Homogeneous mode, additionally, for a short moment the engine around 20% “spits” in the exhaust system to quickly heat up the NOx catalytic converter.

Note: wear of the NOx catalytic converter is indicated very approximately and its performance in current conditions can differ. Unfortunately, even in most optimistic scenario – with perfect driving profile (long driving sessions in even conditions with high average speed), as the practice shows – by 80 .. 100.000 km the performance of NOx catalytic converter reaches the level, when the regeneration happens max often, desulphation sessions – not less than after each 700 .. 1200 km.


Here, how the average car (with the average wear of NOx catalytic converter and OEM NOx sensor) work profile looks – in the upper part of the image:

In the bottom part of the image – so looks the engine profile, if NOXEM is installed (not depending on the condition of the NOx catalytic converter).

With OEM sensor the regeneration happens after each 10 .. 15 seconds, almost half of all time Stratified charge actually is not turned on, accordingly – the efficiency of this mode is not used in full amount. In turn, with NOXEM the regeneration happens for around 5 times less often (after each 55 .. 60 seconds), which also ensures lower fuel consumption, because at least 90% of all time the engine works in Stratified charge.


But, returning to the problem.

This problem will not be observed:

  • at idle (except one-time shivering of the engine in a moment, when in idle the engine one time switches from Stratified charge to Homogeneous mode);
  • in the mode of high load (because then the engine works in Homogeneous mode);
  • for the cold engine (because also then the Stratified charge is not activated).


How to recognize exactly this cause of the problem?

Turn on INPA, open fuel mixture menu ../F5/F6 or mode menu ../F9/F1 and indicate the moment, when the shivering is observed. If this moment coincides (preferably check the coincidence for several times) with the moment when the engine for short time (for several seconds) switches to the Homogeneous mode and Lambda drops below 1.00, you have got the confirmation – misfires are exactly at the moment on the switching between modes.

Additional confirmation – switching between modes (changes of Lambda: reduction from 1.4 .. 3.0 to 1.0 and back) happens very quickly (in parts of second).

Additionally: using ../F9/F1 and switching modes manually in idle, the switching process is uneven, with strong shivering of the engine.

Note: after using manual mode, don’t forget to switch back to the DME management!


What else to check, before get started to software upgrade?

For sure you have to check DISA valve (valves) and it’s (their) performance. Check the real performance – movements of the mechanical part, and also the airtightness (not only O ring, which seals intake manifold, but also O ring, which ensures the airtightness of the valve itself in a closed condition). Even small problem with airtightness of DISA valve can cause totally inappropriate fulfillment of cylinders in the swiftly changing situation (what are the regeneration session inquiries and change of engine mode)! If with DISA valve (valves) everything is in technical order, unfortunately, we have to move to a more complicated part – software upgrade.


With what to upgrade the software?

For this purpose, ISTA P and WinKPF will suit. From hardware tools: OBD/USB cable or ICOM. ICOM, in turn – China clone or OEM tool.


Advantages of ISTA P:

  • easy to use tool;
  • ensures upgrade of all car modules (upgrade of Integration level).

Disadvantages of ISTA P:

  • instead of an upgrade of one block usually, we have to upgrade all car – the process can take a significant amount of time (additionally – you have to take care for charging the battery during programming time);
  • you can not choose software versions from other FR car (this is possible only for MSD80) or older releases.

Advantages of WinKFP:

  • quick programming of DME (without exaggeration – several minutes);
  • you can program versions from other FR car (MSD80), choosing also older software versions.

Disadvantages of WinKFP:

  • a bit more complicated in using, comparing with ISPA P;
  • you have to find and import appropriate SP Daten files.


For my own car I have performed programming with OBD/USB cable – no problems, but for another car, I would suggest ICOM (this is a more safe solution).

WinKFP is not available in dealer center, only software available there – ISTA P. The dealer takes the request to update the software as a tooth-ache. Programming takes a lot of time, during it the ICOM complex is busy (it can not be used to diagnose other cars), sometimes happens to brick some block. Have to make sure, that there is a continuous charge of the battery – the work is very unpleasant. Yes, now the situation is better – ICOM costs only around 1000 .. 2000 EUR, but earlier, when GT1, later SS/SSS, were in use, the situation was much worse – equipment cost at least 10 .. 15.000 EUR! It’s clear, that for average dealer center, possibly, had only one or two sets of these tools. For this cause, the software of many cars never has been updated and DME contains very old software releases.


Several nuances, which I have observed, when programming DME:

  • MSD81 contains additional control algorithms of hardware/software, which means – “wrong” FR software programming is not possible (opposite MSD80). True thou, usually newest MSD81 software releases work relatively correctly and such programming of “foreign” release is not relevant;
  • with MSD80 can happen, that the better is not “newest/last” release, but one of previous. Accordingly – preferably use WinKFP, so you have options to choose the best version;
  • with MSD80 can happen, that better is a version, intended for some other FR (such situation indicated both for N53B30U0 and N53B30O0 engines) – for example, versions, who are intended for iX cars, turned out to be with “softer” performance (with lower sensitivity to uneven road – error message 3104);
  • if in MSD80 the software, intended for other FR, but with correct/appropriate functionality is recorded, in the error message memory (only) the error message 2FA3 is recorded. This error message doesn’t affect the performance of DME in any way;
  • if the error message 2FA4 is recorded – a signal, that the functionality of recorded software don’t correspond the exact engine, engine performance in limp mode – guaranteed;
  • if correct version (in means of functionality) is recorded, re-adapting of the engine is not required. The result can be evaluated immediately;
  • when programming with WinKFP, review all available software versions both in MSD80 and MSD81 data folders. There are SP Daten sets, where the content of these folders is switched by places.