A month ago, my F32 was hit by a doe. As if nothing special, but still – the headlamp had to be replaced, the front bumper was damaged too. The car was towed to the repair service center. After almost 4 weeks of waiting, I finally got a message that the vehicle was repaired.
When taking a test drive, I noticed two problems:
a. AC is not working;
b. The idle is unstable, and misfires can be felt regularly.
Solution of the ACV problem I let to the repair center. Till the “attack” of the doe, it was performing flawlessly. If, for example, the AC radiator is damaged – I can not repair it myself.
The opposite is with misfires – I decided to solve this problem immediately. The situation was more than strange:
a. as far as I remember, there was no such problem till the last day the car was running before repair;
b. the spark plugs were replaced 15’000 km ago, and NGK was installed (yes, not BMW, because there was 0 available in the local dealer’s warehouse);
c. some kind of spark plug oxidation has happened? Does not sound credible. After driving 20 .. 50 km, the problem did not disappear;
d. some defect of the ignition coil?
e. some other problems have appeared? For example, incorrect fuel mixture? VANOS, Valvetronic problems?
As a first step, I checked the overall fuel mixture with ISTA. It was correct: Wideband Lambda probe reports Lambda 1.00 .. 1.01; control probe: around: 0.25 .. 0.35V.
Here, the analysis of the exhaust gases confirms that everything is perfect with the average fuel mixture:
VANOS positions are correct and stable. Rail pressure: stable.
I turned on the Expert mode; here is how 2 .. 3 minutes look:
As we see, the average mechanical efficiency of all/each cylinder is identical. So – the cylinder’s individual fuel mixture is correct, too. The short-term mechanical efficiency differs from the ideal up to +/- 6 .. 10 units, which means – the mechanical efficiency of cylinders in the short-term is unstable; the difference from the ideal is enormous – up to +/- 15%.
In addition: idle RPMs – unstable, fluctuates regularly.
Misfires are happening in different cylinders. Yes, cylinders No.1 and No. 2 dominate, but cylinders No.4 and No.6 also have some misfires time by time.
As we see, DME, too, registers these misfires; the misfire counter is not 0 anymore.
Conclusion – The ignition coils are not to blame. If the problem is in one certain cylinder, the defect of the ignition coil would be a credible scenario. But 2+ ignition coils can not be damaged at the same time.
Spark plugs? That is the only logical explanation. What happened to the spark plugs?
I got in touch with the local BMW dealer – yes, there are (even) 20 units in the warehouse! And, what is the most interesting part: exactly BMW NGK. So, I will have a great option to compare these BMW spark plugs with already installed NGK spark plugs (I took pictures before I installed them).
For the information: the list price of the NGK spark plugs is EUR 16/piece, and the list price of the BMW NGK spark plugs is EUR 26/piece.
Here are several images of the installed NGK spark plugs:
And so the BMW NGK spark plugs look:
Yes, BMW spark plugs look more nicely done. Welding of the central electrode – neater. Side electrode – not only cut out but also polished. And still – the visual differences are not significant. Of course, a correct comparison would require appropriate equipment (spectrometer, with which to identify the material of the electrodes). Still, in defense of the “regular” NGK spark plugs, I have to mention that this model has (according to the NGK catalog) a central electrode of iridium and a side electrode of platinum. Planned resource: 100,000 miles (so – more than 100,000 km).
Have I purchased visually fine, but technically – very poor quality counterfeits?
I did not get to the replacement of the spark plugs because I got a message from the repair service center that they were ready to check the AC problem. Before delivering the car to the service center, I checked the error messages and live data:
As we see, there is a problem with the indications of the pressure sensor. Even when turning off the compressor, without evaporation of the reagent, the pressure before the sprayer is 27 .. 30 bar. IHKA does not even manage to turn on the compressor – for several seconds (when the indications of the sensor “fluctuate” in the range of 27 .. 31 bar), the critical threshold of 30 bar, when the compressor is turned off permanently, is reached.
It turned out that the pressure sensor connection was damaged by performing an incorrect repair (the cooling radiator was damaged too by the “attack” of the doe).
Here is the schematics of the connection:
As a result of the defect, the PIN1 connection was lost. The sensor had only a +5V connection from PIN3, and this 5V voltage potential (slightly dropping in the sensor’s electronics) via PIN2 (output/signal) came to IHKA. IHKA reported these data as high pressure (27 .. 31 bar).
On the same day, I got my car back with a performing AC. But the most interesting part only followed – the problem of the misfires had disappeared! Idle – perfect! Here is how it looks now:
Could it be that the situation has changed because there is an additional load on the engine (AC compressor)? I turned off the AC and waited for a moment – no, no misfires anymore!
What happens if IHKA has previously mentioned problems? Is multi-ignition switched off? Injection strategy changes? Rough software mistakes, for example, the ignition is managed with “jumps”?
No, the situation is much more straightforward!
If DME and other modules of the vehicle are working as planned, DME receives information regarding mechanical load to the engine, created by all “consumers”:
a. regarding load created by the alternator – from the alternator itself, via LIN bus;
b. regarding electrical water pump (if such is present) – from the water pump itself, via LIN bus;
c. regarding the mechanical load created by the steering wheel while turning it – from the DSC module or the steering column module EPS (if the electrical power steering is present);
d. information from the gearbox (if it is automatic) via CAN bus;
e. information regarding the load created by AC from the IHKA module;
f. electric cooling fan (managed directly by DME).
Note: this list may not be complete and could differ for your car.
All this information is critically necessary to ensure a quality idle. By knowing the load created by each hub and the changes of this load, DME can react immediately and maintain a perfect idle – DME can immediately calculate how mg of additional fuel and how much dm3 air is necessary to compensate the Nm of load created at the exact moment. This calculation is performed in the range of the energetical module principle. This principle intends that DME is electronically simulating the performance of the engine cycle by cycle, all known parameters (injector flowrate; air amount, its temperature, density; Rail pressure; mechanical load, energetical efficiency of fuel, etc.) continuously comparing them to calculated/simulated ones and making conclusions to ensure perfect performance of the engine.
Instead, if any of these hubs are damaged, DME is unaware of the existing and planned mechanical load. Accordingly, it has to work with “old” methods – reach post factum. In this case – DME tries to maintain the required RPM using simple methods (working in closed-loop mode).
This task is not simple. DME is not able to react immediately to swift changes in the performance (and load) of the engine when RPM already does not correspond to the ideal. Both Valvetronic and throttle (and even more – the air in the intake manifold) have inertia. Yes, DME corrects the amount of injected fuel with max speed, but it gives some short-term non-optimal fuel mixture. Consequences? If DME wants a swift (even slight) reduction of idle RPM, the fuel mixture in the actual cylinder in the appropriate cycle is lean. And – misfires happen.
Why the “old” engines did not manifest such problems? For old engines, the port injection method was used. The fuel was mixed with the air for a long time and in good quality; both lean and rich fuel mixtures burned well. DI engines (and B58 is exactly that) work in “Layer” mode – with stoichiometric fuel mixture (Lambda = 1.0), but without creating an even (Homogenous) fuel mixture. Why so? Because B58 has a very high compression – by using a Homogeneous mixture, it would be a huge possibility that self-ignition happens. For this reason, the fuel is injected in several portions, the last portion – exactly at the moment of ignition. Yes, the problem with self-ignition is solved, but such an injection strategy is much more capricious. Even a slightly leaner fuel mixture has an option not to ignite.
This time, IHKA damage: error message regarding pressure – it is a critical defect. The reason for the error message can be a damaged AC compressor, too. In such cases, IHKA data regarding the planned mechanical load of the compressor can be incorrect. So, to avoid much more severe problems (engine stalling at idle if it turns out that the compressor creates a more significant load than reported by IHKA), in such a situation, DME chooses to ignore data of the mechanical load.
Sentence of this entry – If you want DME to perform correctly and that idle is of high quality – maintain all previously mentioned/connected modules and hubs in good technical condition! Yes, even in winter, AC should work; yes, even the error messages of the DSC module can have an impact on the performance of the engine, not even talking of gearbox, electrical water pump, and alternator!
