After replacing the ignition coil of the 5th cylinder, the crash in idle disappeared (defect described here).
So – my engine had problems with the ignition coils of cylinders No.5 and No.6.
Why did I choose the ignition coil as a culprit? Other possible options:
a. spark plugs. Replaced – new BMW spark plugs installed (after 3rd crash event). So – dismissed;
b. injector, stuck in a closed position? It’s not a realistic scenario – the fuel smell can be felt strongly. Stuck in an open position? No: Rail pressure remains stable; lean mixture/adaptations are fixed during the crash;
c. wires and plugs – don’t correspond to the specifics of the defect. In addition, via the wires and plug of the ignition coils, large current flows. In case of such a defect, the plug would melt. Such defect was not observed;
d. DME, Ignition switch. I assume that this will be the most popular version for many, so – a bit more about this.
DME is contained in a plastic bracket fixed to the engine on the side of its intake manifold. There is no (except the engine block) other significant heat source. The temperature around the DME does not change significantly to create radically different temperature conditions in idle.
The temperature conditions of the DME itself are not specific to the idle either. In idle, the Ignition switches are used relatively rarely (only 5.5 times/second); a much heavier work mode for these components is by higher RPM.
Even if we assume that this is damage to some switch, such a defect does not correspond to the operating characteristics of a semiconductor switch. If (for example, due to overheating) the switch would have such a significant current leakage that the management of the ignition coil would be impaired, the switch would be damaged/destroyed – immediately. In my case – at least 7 .. 8 such crashes, but – the correct engine performance was restored directly after restarting or drying the spark plug.
No, this is not the defect of the Ignition switch. The defect of other components (for example, management elements of the switch) – from the SciFi series.
What is wrong with the ignition coils? Are they overheating? You will rightly say – well, if the ignition coil is failing in such a manner, its thermal conditions should be extreme! Even more – extreme exactly in idle! If the temperature of the ignition coil is stable, all theories regarding thermal overload (exactly in idle) will evaporate in the air!
I equipped myself with a thermal camera and started the tests. The angle of the thermal camera:
a. outside temperature around 8 oC;
b. weather – wet, cloudy, raining time by time. Asphalt/ground temperature corresponds to the temperature of the environment.
After driving with an average speed of around 90km/h, I stopped and cooled down the engine for 10 minutes. After this pause:
a. 1st cylinder ignition coil temperature around 54 oC;
b. 5th cylinder ignition coil temperature around 67 oC;
c. 6th cylinder ignition coil temperature around 71 oC;
the temperature of the ignition coils of the 2nd to 4th cylinder – increasing slightly.
I turned on the engine at idle. After 10 minutes:
a. 1st cylinder ignition coil temperature around 62 oC;
b. 5th cylinder ignition coil temperature around 79 oC;
c. 6th cylinder ignition coil temperature around 82 oC.
After 20 minutes:
a. 1st cylinder ignition coil temperature around 63 oC;
b. 5th cylinder ignition coil temperature around 84 oC;
c. 6th cylinder ignition coil temperature around 86 oC.
After 30 minutes:
a. 1st cylinder ignition coil temperature around 64 oC;
b. 5th cylinder ignition coil temperature around 89 oC;
c. 6th cylinder ignition coil temperature around 92 oC.
At this moment, I took pity on the ignition coils – it was clear that the temperature continued to increase, and the problem here is catastrophic!
Then, I performed a 30-minute drive with an average speed of 80 .. 90 km/h.
a. 1st cylinder ignition coil temperature around 35 oC;
b. 2st cylinder ignition coil temperature around 50 oC;
c. 3rd cylinder ignition coil temperature around 60 oC
d. 4th cylinder ignition coil temperature around 55 oC;
e. 5th cylinder ignition coil temperature around 45 oC;
f. 6th cylinder ignition coil temperature around 45 oC.
Here’s how interesting it looks. On the go, the ignition coils of the last cylinders are cooled down very well. Instead, in idle, the ignition coils of the 5th and 6th cylinders heat to inadequate temperatures.
Around 90 oC and continues to grow – it’s a catastrophe! What is the reason for such a temperature?
a. the exhaust heats the air, which (according to the physics laws) moves upwards along the engine block;
b. the decorative engine cover perfectly catches this hot air and leads it directly to the ignition coils.
What will be the ignition coil temperature if the outside temperature is +30 oC? If the asphalt temperature will be 50 oC? If the car drives for short moments and the exhaust temperature increases even more? And what about a larger load, for example, turned-on AC? 110 .. 120 oC? More? And inside the ignition coil? Till 140 oC?
There is a real fail. Multi-ignition in such a condition is deadly to the ignition coils. It is strange that during the 8+ years since the B58 engine was offered to users, BMW has not managed to solve this problem.
It is interesting that in N43/N53 series engines, if the car is held idle for a longer time (2 .. 5+ minutes), the Mapped mode is turned on (with a coolant temperature of 80 oC), and the cooling fan is activated to almost full power. These techniques radically reduce the temperature in the engine compartment. Bosch DME does nothing of it…
The N53 series engines (3.0-liter versions) had additional cooling channels for the exhaust manifold installed. B58 engine – although it is much more powerful (and creates much more heat), such additional exhaust cooling is not intended!
It looks like there is no progress, but regression has happened. There is a feeling that Bosch (and BMW AG team, too, unfortunately) for the last decades have been living isolated from civilization.