The owner of F10, 523i approached me for help. The car can not be driven normally – strong vibration can be felt for the cold and warmed-up engine. The engine does not give full power, strong shivering can be felt. This problem is stable, observed all the time. Also for the warmed-up engine, after a long drive, driving evenly (in conditions, when DME could remeasure the injectors if it would require such necessity, and prevent troubles, if possible).
Part 1. NOx system and vibration
Checking the error message memory, I detected, that the only fundamental error message is regarding the NOx sensor.
There are misfires in cylinder No.3. For granted: if there is vibration – special attention should be paid to the performance of cylinders and injectors.
The car was inspected directly after receiving it in service, the engine – warmed up till working temperature.
Live data indicated so incorrect mechanical efficiency of cylinders, so it was not possible to indicate, which cylinder is damaged. Each cylinder had its “personal”, significantly different mechanical efficiency. Each of the cylinders was misfiring regularly. It was decided to delete all adaptations,
Next step: evaluation of the performance of the mechanical efficiency of cylinders with cleared cylinders (old: previously created) individual adaptations and disabled warm-up of the Lambda probes (the engine works in open-loop mode).
Mechanical efficiency of cylinder No.3 looks very strange, Is there really a problem with the injector of cylinder No.3? Does it not opens us much as necessary or is clogged?
Menu of injector corrections shows strange data: cylinder No.3 by the reduced opening coefficient, the mechanical efficiency is reduced. That would be as if logical, but there is a question – why the opening of the injector for this cylinder is reduced if the efficiency of the cylinder is below the norm? Coefficients of engine idle evenness – stably elevated:
Note: DME contains several multi-dimensional adaptations maps for each injector. Just a part of them is cleared when the service procedure ”Delete adaptations” is performed. The remaining data is renewed during the re-adaptation of the engine. In this case – hidden (and not cleared, typically – delay and flow-rate data) adaptations still are affecting the injection time of injectors.
When Lambda probes start the warming-up, fundamental problems in bank No.2 appear. One of the injectors is leaking strongly:
Even HPFP works in emergency mode with reduced pressure (correct pressure: 200 Bar)!
What to do in this situation?
There are many “specialists” who claim that the NOx system is very insignificant, that the biggest harm, that can be caused by the defects of it – the fuel consumption will be slightly increased. They claim, that it could be even “turned off” – deprogrammed. Or at all – just ignore the problem and continue to use the car.
I argue – the NOx system is critically important for these engines, problems of this system create fundamental disfunction of the engine performance!
If the NOx system is damaged, the engine does not use Stratified charge (because during this injection mode a larger amount of nitrites is emitted – to protect the environment, using this mode is allowed only in case, if both NOx sensor and NOx catalytic converter are in working order). Unfortunately, a range of specific measurements is possible only in a Stratified charge. Several of them:
- measurements of the injector atomization (quality of injected “mist”);
- measurements of injector leaking in a closed position;
- measurements of injector delay parameters for short openings and separation of these data from leaking.
All these injector measurements are performed regularly in different driving conditions. If there are no injector measurements, the engine is not able to adequately evaluate the “health” of the injectors, it does not create their adaptation maps and is not able to apply the correct corrections.
To understand at all, which injector is damaged, in the existing situation initial repair jobs were done:
- solved problems of the NOx system – NOXEM was installed;
- the engine was re-adapted.
Here, the situation after the first stage of repair. The Homogeneous mixture, the engine warmed up:
Here – Stratified charge:
As we see, all the problems of the warm engine are gone! No vibration, no misfires!
Here, more clear can be seen, that the engine (after a long time) uses Stratified charge again:
Do you see the marked offset type LTFT of the 2-nd bank? Leaking of some injectors in this bank has not disappeared! But at the same time – the engine works without any vibration, no misfires observed, all problems are gone!
The only repair, what was performed to the engine – problems of the NOx system solved.
In my opinion, irrefutable proof, that the “health” of the NOx system is critically important to the normal performance of the engine! Here – DME remeasured injectors in Stratified charge mode, has compensated all their defects, and the car works as new!
Of course, leaking of the injectors has not gone anywhere – leaking injector(s) has (have) to be replaced. But now, unlike the initial situation, the defects of the injectors can be seen, because they have adequate corrections applied, and measured parameters of the injectors and mechanical efficiency of cylinders are plausible.
Part2. Problems of the injectors
To evaluate the leaking of the injectors for a cold engine, wait for the next morning, for the engine to be completely cold.
Cold start of the engine showed the following picture:
Here, the Lambda probes have not reached the Stoichiometric mixture in the banks (in both banks, the mixture is rich, larger problems are in bank No.2), problems are for:
- the injector of cylinder No.1 of the 1-st bank;
- injector of cylinder No.5 of the 2-nd bank.
Remaining 4 injectors are performing correctly.
Injectors of the 1-st and 5-th cylinder were replaced, encoded, the engine was readapted.
Here, the result during the next cold start:
Mechanical efficiency of cylinders – perfectly even.
Here, the corrections of the injectors and mechanical efficiency of cylinders:
Result for problematic (3-rd cylinder with the false problem and actually problematic cylinders No.1 and No.5) cylinders – perfect! Not the smallest problem!
Here, DME has created multiplicative LTFT, works in Stratified charge:
One more repaired BMW.
Well, this is not uncommon. More interesting, in my opinion, is another aspect.
What information would be seen by the diagnostics specialist in the BMW dealer center (remember – INPA is forbidden in dealer centers)? Misfires of cylinder 3.
What do TIS/ISTA recommendations say? Replace all injectors of bank No.1. The bill to the customer would be more than EUR 1000.
Would the problem be solved? No, because the largest (main) troubles were with the injector of cylinder No.5 (2-nd bank)!
Let’s make the situation for the diagnostics specialist easier. Let’s assume – he has INPA available. Let’s return to the initial situation (2-nd and 3-rd image of this entry). Completely incorrect mechanical efficiency and correction data of the injector of the 3-rd cylinder! Here, as if several confirmations that exactly the cylinder No.3 has problems! The injector of cylinder No.3 should be replaced? It has no problem at all!
The moral of the story – if the NOx system of the N53 series engine (also for F-series cars) is damaged (and, accordingly, the engine has problems with injector measurements in Stratified charge, because this mode is turned off), injector measurements and corrections, applied to them, could be (and usually are, because the parameters of the piezo injectors “float” quite quickly and in wide range) completely incorrect! Based on these incorrect data, you will spend a lot of money, replacing correctly performing components. For this reason, the NOx system has to be replaced as first!
Why DME has “screwed up” the adaptation data of the injector of the 3-rd cylinder?
The firing order of the BMW 6 cylinder engine: 1/5/3/6/2/4. As we see, the firing of the 3-rd cylinder is directly after the damaged 5-th cylinder. Obviously, because the DME was not able to measure the leaking of the injector of the 5-th cylinder (it can be measured only in Stratified charge), it falsely assumed that the increased turning speed of the flywheel is a “merit” of the next injector (of the 3-rd cylinder). If any cylinder has a mechanical efficiency, different from ideal, the flywheel actually “fluctuates” because it has a large mass – its necessary to reduce short term unevenness of its turning. So – from one side: the task of the flywheel is to reduce the turning unevenness, from the other side – DME has to try to measure this unevenness. DME reduced the opening time of the injector of cylinder No.3, the fuel mixture in cylinder No.3 became lean, its efficiency was reduced. Now the average mechanical efficiency of cylinders No.5 and No.3 was correct, but the engine eas vibrating strongly – logical consequences. Because of too lean fuel mixture, misfires started in cylinder No.3. DME identified this problem correctly, recording an appropriate error message in the error message memory.