This time – an interesting case with F32 with B58 engine.
The car with a warmed-up engine runs in idle. Suddenly, I felt several shiverings; then the engine started to vibrate, and the idle slightly dropped. After a second or two, DME stabilized the idle, but the vibration was still present. After around 5 seconds, a shrieking sound appeared from the engine room. The sound is as if the drive belt of aggregates is slipping. My first thought was – problems with the alternator or, for example, the AC pump?
I pressed the accelerator pedal slightly to increase the RPM. Stop – the shrieking sound did not change! Not even a little! PRM increased, but the sound stayed precisely the same! How is that possible?
After some 10 seconds, the shrieking sound disappeared; the typical engine performance was restored as if nothing had happened. The only thing that confirmed some problems was smoke from the exhaust pipes and a sharp smell of the exhaust gases. EML (Check engine) did not light up, we can assume – the defect is not critical.
True thou – the smoke from the exhaust was impressive:
What happened to the car? I will leave the answer to the end of this entry. At this moment, I will pretend that I am a user ”vulgaris”. My car experienced such symptoms, and I arrived at the dealer center to find out what the problem was and what should be done to solve it. It should be added that after this occurrence, the engine continued to work normally – nothing indicated any problems.
When opening ISTA, we see an active (I connected the diagnostics equipment immediately, without restarting the engine) error message regarding the incorrect amount of inlet air. And – that’s it.
Let’s check the time scale:
Yes, this problem (in the foreseeable past) was recorded only for one time.
The attributes of the error message are quite interesting:
LTFT is correct. At the same time:
a. Valvetronic has been turned off (opening of the inlet valves close to 10 mm);
b. short-term fuel correction was +30%, fuel mixture (initially) – lean.
The note that the engine runs in mode 2, seemed quite interesting to me. What is mode 2? As usual, there is no explanation in BMW materials. We can assume:
a. mode 1 = open loop; Valvetronic deactivated;
b. mode 2 = closed loop; Valvetronic deactivated.
Returning to the diagnostics: unfortunately, the error message and its attributes don’t give a clear answer to what happened to the engine. The depression in the inlet manifold was correct. No error messages regarding throttle or other hubs.
Next step – choose “Calculate test plan”. And here is the description regarding possible causes of the problem. Anything possible could be the one to blame: inlet manifold, exhaust, injection, fuel supply. That is a great description!
Reading this sounds promising!
As a next step in the diagnostics, ISTA offers to check the cylinders.
Test in the process:
When performing this test, ISTA sequentially switches off each cylinder. What and how is measured during this test – no exact information from the manufacturer. Logically thinking during these tests:
a. incorrect performance of the injector can be checked (controlling Lambda by using a wideband probe in the exhaust);
b. fundamental defects of the piston group can be checked (controlling the changes of the mechanical efficiency – if any cylinders have fundamental damages, the mechanical resistance created by it in the turned-off position will differ).
After this test, ISTA performed one more test in which it repeatedly switched off cylinders sequentially. This test has 18 steps – 3 steps for each cylinder. I assume that during this test, ISTA tried to find a leaking injector. An interesting nuance is typical for the performance of the injectors: defective injectors are leaking more actively if they have been opened just now. If the injector is closed, its leaking slowly reduces. Accordingly – if the cylinder is switched off (and the injector closed) for some time, it is possible to evaluate the performance of the injector after the “pause” according to the performance of the cylinder directly after restoring its performance. I would like to remind you – this is my version of what is done during these tests. The manufacturer does not give any information.
Next stage of the test – a special menu for the “preparation work”:
A second test in progress:
And here, the tests are completed. Everything is perfect! Isn’t an excellent diagnostics?
I checked the fuel mixture live data:
As we see, everything is correct! LTFT – very close to 1.00; Lambda 1.00; control probe confirms correct Lambda.
I checked the mechanical efficiency of the cylinders:
Everything is fine; the mechanical efficiency of cylinders is +/- 1 .. 2%; efficiency regularly changes the “polarity”.
What actually happened to the engine?
A damaged inlet manifold, which defect disappeared? Damaged throttle? Damaged air mass meter? Is the damaged inlet pressure sensor?
This time, we have to go back in history. How does the misfire’s identification happen? Siemens was the one who, as the first, managed to patent the principle: detection of misfires based on the change of the turning of the flywheel. If the misfire happens in the cylinder, the flywheel “slows down” a little. This principle was working well enough (I admit it even not looking at the false misfires in the initial SW releases of the N53 DME). The competitor Bosch patented another principle – the use of the accelerometer to detect the misfires. If the misfire happens in the cylinder, the vehicle (on the go) slightly slows down. But this principle has a shortage – it does not work in idle! If DME is mounted on the engine and the accelerometer is placed inside it (and measures the shaking of the engine), theoretically, this idea should work in idle, too, but in reality, we have what we have.
What happens if the misfires start in any of the cylinders? And – what’s important – exactly in idle?
Bosch DME does not see if the (group) misfires have started in idle. More exactly – “pretends” that it doesn’t. All symptoms indicate that Bosch, too, analyzes the acceleration of the flywheel to detect misfires (anyhow – he analyzes the acceleration of the flywheel to measure the mechanical efficiency of cylinders and does not hides this functionality). But, for understandable reasons (to not grossly infringe the competitor’s patent right), it does bad enough.
So – Bosch DME sees that in idle (as if unexpectedly, as without understandable reason), RPM drops. The drop of RPM is swift and strong. To maintain the idle, DME switches in emergency mode. The first one, which is turned off, is Valvetronic. Nevertheless, the situation does not improve this time (Valvetronic is not to blame). To maintain the idle, DME has to significantly increase the energy – amount of the fuel burned in cylinders. To keep the Lambda around 1.00, DME has to increase the amount of air in cylinders. As we see from the attributes of the error message, the amount of fuel increased by 30% (compared to the planned one). It is clear that the amount of the sucked-in air is increased (by the same 30%). Yes, 1/6 of the fuel and air is wasted – it burns in the catalytic converter (because one of the cylinders has misfires – if it does not perform the useful work). DME, instead, has to “pretend to be a fool”- it is not allowed to identify the misfires! What the DME “sees”- increased amount of air in the inlet manifold (compared to the planned). And regarding this, the error message in the DME error message memory is recorded.
What is that shrieking noise from the engine compartment? No, it is not a drive belt. It is not a mechanical problem. It is the drying procedure of the spark plugs! Already since N43/N53, if DME identified misfires in any cylinder, it started to apply the spark plug drying procedure:
a. injector of the damaged cylinder was turned off;
b. the ignition coil was continuously activated, trying to dry the spark plug with a continuous spark.
Yes, the ignition coils of these engines created that shrieking noise, too, but that sound was efficiently muffled by the decorative cover of the engine. Inside the cover is a sound insulation material (several cm thick), which efficiently muffles both the ticking of the injector and the noises created by the ignition coils.
It looks that in the case of B58 series engines, the situation is slightly different:
a. as DME is forced to pretend that it does not notice in which cylinder the misfires are, it has to start the drying of all spark plugs in all cylinders;
b. unlike the N43/N53 series engines, the cover of the B58 series engine is a thin decorative plastic, which is not an efficient sound muffler.
Six ignition coils, activated continuously – the noise is impressive!
So – although the Bosch DME does not see the misfires in idle when it notices reduced mechanical efficiency, DME assumes that the cause of it can be misfires. This is logical. The bad thing is that as DME can not see exactly which cylinder is defective, the injector of this damaged cylinder is not turned off. It, instead, means – the unburned fuel and air burns in the CO catalytic converter, overloading it significantly.
Needless to say (directly after the defect, without restarting the engine), misfire counters, indicated by ISTA, look like this:
Here, I have to note – that misfire counters, reported by ISTA, are nullified 3 .. 5 seconds after the event. So – if you do not perform the log recording via Expert mode or don’t observe these counters during the defect, they are entirely useless.
To make the situation even more “interesting”:
a. for vehicles with a manual gearbox – a misfire is recorded each time the gear is switched;
b. (long-term) misfire data, reported via OBD Mode 6, are nullified when the DME error messages and/or the adaptations are deleted.
This time, the cause of the problem is trivial – misfires. And it looks like the problem is not connected with injectors. Obviously – there is a defect/wear of the spark plugs or the ignition coils. The spark plugs are NGK (not BMW), with mileage of around 25 .. 30.000 km; regarding the results after replacement of the spark plugs – in continuation (here).
