There won’t be many pictures in this entry. The reason – the owner of the current vehicle lives 2000km from our location and practically all the information about the problems I received in e-mails. I had very limited access to the information – I received only as much as the owner “dispensed”. It was his choice. How it ended – read further. In my opinion, this case is very educating to not repeat the experience of this BMW enthusiast.
Around one year ago, an owner of BMW F10 approached me with a typical story: the car has mileage ~190.000km, in the DME error message memory – error messages regarding NOx sensor. The car was driving with a damaged NOx system for a long time already, problems of uneven performance were “solved”, replacing all possible hubs. When the ideas for chaotic replacement of different hubs were finished (or – the owner of the car got fed up with a waste of money or run out of it), the owner of the car decided to try the NOXEM. Yes, the local “specialists” continued to claim that the NOx system does not affect anything, but… After a longer communication and many confirmations that the NOx system, however, is very important, the owner of the car decided to purchase and install the NOXEM.
The car came to life! Yes, some sort of unevenness was still here during the cold start but the owner of the car did not start to solve it. Probably, in his opinion, that is OK, that cold engine shivers. Probably, the local “specialists” claim that is OK.
After one year, the owner of the car got in touch with me and reported that the error message 12C401 appeared in the error message memory of the car. Deleting of adaptations don’t help.
I drew the attention of the owner of the car to the reasons why this error message is recorded in the error message memory but he was not interested in so complicated things. The local “specialists” have said: as there is an error message regarding the NOx sensor, it has to be replaced. I asked to send me DME live data to find out the reasons, why the Stratified charge is forbidden – unfortunately, the owner of the car did not give any information.
After a short moment, the owner of the car sent me a message that he has installed an OEM sensor and the shivering of the warm engine is gone now. Problem solved!
Excuse me? Shivering of the warm engine? This problem was new to me. A pity. If I would know about it I would suggest the solutions. But it was the choice of the owner of the car, regarding which problems to inform me and which problems to elide.
In his opinion, the problem is solved, but I claim – new problems are caused, EUR 500 is spent useless, and the “funniest” is only to come!
Why I have such a belief?
1. Most part of parameters (Lambda linear, Lambda binary, temperature) NOXEM measures and sends to DME in real-time mode. In addition, DME requires the regular and immediate following to the commands of the management. If even one parameter will be incorrect, DME immediately will record a list of error messages regarding defects of the NOx sensor (12C501; 12C502; 12CA01; 12CA02, etc.). Obviously, the signals, measured by sensor, correspond the truth. The NOx signal instead is calculated mathematically and can not be “damaged” during the time. If for a year DME “satisfied” with such signal but now suddenly something has changed – I believe, even for a technically not educated person is clear, that something has changed on the “side” of the car.
2. In my experience (several thousand of these current engines) I have seen only 2(!), for which the NOx converter was in working order after reaching the mileage of 200.000km. Both of them were driving on German highways and were maintained in a perfect technical condition. Accordingly, theoretically the possibility that the NOx converter of the current car (described in this entry) is in working order, is 0.1%. In reality, such a possibility is 0, because the car was driving with a damaged NOx sensor for a long time before installing the NOXEM. For such car, when installing an OEM NOx sensor, the Stratified charged is turned off immediately and is never turned on again, because DME receives information regarding bad NOx catalytic converter! Yes, N53 series engines of F series do not inform the user of the car for such a problem (such strategy of hiding problems was chosen by BMW to reduce the number of reclamations).
3. I have no reason to not believe the owner of the car that after installing the OEM sensor (regardless it’s new, used, able to work or with a hidden typical defect) shivering of the engine disappeared. Why so? The owner of the car informed me about the shivering of warm engine post factum – already after performing the “repair”. It’s a pity because if he would do it before, he would save EUR 500. One (and typical) of causes of the problem – misfires. Misfires are one of the reasons why the car shivers and why DME (seeing such “shivering”) forbids Stratified charge time by time, but the error message 12C410 is recorded in the DME error message memory. A paradoxical situation is emerging: the sensor, which informs regarding an excellent performance of the NOx catalytic converter, causes the shivering of the engine, but the sensor, which informs regarding damaged NOx catalytic converter, “solves” the problem?
The engine injection mode (and accordingly – Lambda, VANOS and parameters of other hubs) are defined by DME. The NOx sensor defines, would the DME allows a Stratified charge or not. The rest is up to DME. Accordingly – the NOx sensor does not cause the shivering of the engine. It’s caused by a Stratified charge!
Now we reached the most interesting part – why warm engine shivers in Stratified charge but does not shiver in Homogeneous mode.
Actually – the engine shivers also in Homogeneous mode, for example – cold engine, or – when increasing the required torque (kick-down mode). These are the conditions that are harder to ignite the fuel than in low load mode. This car was for sure shivering for a longer time in cold start mode (the information I received from the owner). It is possible, that the owner of the car considered such “behavior” of the engine as normal. Even from “specialists” of BMW dealer centers I have heard statement – it could be for these engines. No, it is NOT normal! The N53 series engine, which is in technical order, even in -25oC starts perfectly! No vibration or shivering!
Returning to the shivering of the engine in Stratified charge – this mode is more demanding to the performance of the ignition system elements and initial parameters of the injectors than Homogeneous mode in low load mode.
There are several reasons for it.
a) In Stratified charge mode, the average fuel mixture is very lean (Lambda 2 .. 3.5). Such a lean fuel mixture doesn’t burn. To solve this problem, the fuel is ignited right next to the spark plug – there the fuel mixture is more rich, in other parts of the combustion chamber – lean. Unfortunately, if the injector “makes mistake” and the fuel mixture on the vicinity of the spark plug is not rich enough, misfire happens.
b) For guaranteed ignition of the fuel mixture, in these BMW engines, specific spark plugs are used – they have a much wider air gap than for “regular” engines. Also, the injection coils are with much higher voltage and power. Increased power increases the load on these components and raises demands to the performance of them, and also shortens their lifespan.
c) If the injector injects the fuel even a bit too close to the spark plug, the spark plug gets wet and misfire happens. Unlike in Homogenous mode, the fuel is ignited in the moment of injection, it has no time to mix with air, and the spark plug has no time to dry. Here, the image from BMW, which shows how close to the spark plug the injector injects the fuel.
The defect of any of the previously mentioned components (spark plugs, ignition coils, injectors) can cause misfires. In addition, these elements are not eternal. The spark plugs serve 20 .. 30.000km (much less, if the engine has increased oil consumption of any injector is leaking or misfiring), ignition coils – can “quit” even after several tens of thousands of km. Also, the injectors of the 11-th release are not without surprises – it happens, that some hard part (rubble, piece of rust, which got in the fuel system) gets in the injector nozzle and the injector starts to leak soon after replacement.
What will be the consequences for the owner of the car?
1. With the OEM sensor, DME does not allow a Stratified charge. And will never allow it again. Unfortunately. With each driving session, the injector adaptation maps will move away from the correct ones. There will be no new data of injectors, their adaptations maps will not be updated. Reason – the most important (for example – leaking and reaction time) injector measurements are done directly in Stratified charge mode. For some time DME will try to work with the old adaptation maps, but when it will not succeed – vibrations of the engine will increase, also the unevenness of the performance and also the load on the CO catalytic converters. After a long time, the car will not be able to pass TI, later – it will not be possible to drive it normally.
2. Even performance, which was mentioned by the owner of the car, is an illusion. The problems are not disappeared, they are not solved. The car shivers during the cold start, after a short while it will shiver also with the warmed-up engine. Already now the unburned fuel of the cold start gets in the exhaust system and permanently damages the CO catalytic converters and Lambda probes.
3. For granted, the car will have increased fuel consumption. If the owner of the car will drive fast enough for DME to start the desulfation session, the average fuel consumption and load to the exhaust system (on already mocked CO catalytic converters especially) will increase even more. The price of the CO catalytic converters is around EUR 1500, cheaper alternatives, unfortunately, are not available.
In my opinion – the owner spent EUR 500 completely uselessly and has caused many problems in the future.
I assume, that after some time when the vibrations appear and problems with misfires increase, the owner will repeatedly start to replace all spare parts, including injectors, because – the error messages in the DME memory will be regarding the performance of the separate cylinders, not the problems of the NOx system… Yes, the “performance” of the BMW with hiding the problems is not correct. Yes, the diagnostics of these engines is difficult. It is true. But exactly for this reason – to save your spendings of unjustified repairs, I have created this blog. Of course, you have a choice – use this information in your favor or do directly the opposite.
