In this entry – continuation of the misfire experiment. If the DME itself does not see misfires, what will happen if I ask it to pay all attention to this problem?
In ISTA, I chose the Misfire detection test module.
The first part of the test is analog to the one described in the previous entry; in addition, the fuel system drop with switched-off pumps was checked. Yes, as usual – no problems were identified.
I was more interested in the second part of the test – “cleaning” the spark plugs. During this test, the spark plugs are heated for 5 minutes to burn off the piled-up carbon. For these engines (B series), the carbon on the spark plugs piles up if the engine is used in the sparing mode.
Why was I suspicious regarding the carbon residues on the spark plugs?
a. my summer trip session via Europe was done, local trips – with low average speed;
b. last several thousands of km where in distinctly calm mode;
c. several times for at least half an hour, the car was held idle;
d. for quite many motor hours, the driving speed was only several tens of km.
Driving profile – catastrophically inappropriate for this engine! And for the desert – a moment before the error message regarding the performance of CO catalytic converters was recorded, I filled the fuel in quite a shady fuel station.
How are the spark plugs cleaned during this procedure? From the manufacturer – zero information. I can imagine two ways:
a. the fuel is ignited at the beginning of the injection portion. Accordingly – the fuel burns in the close vicinity of the spark plug. To make the procedure longer, Rail pressure can be reduced;
b. the fuel is ignited in the moment when the piston (moving up in the compression cycle), “throws” the fuel close to the spark plug. This idea, for example, is used in the FSI engines in VW group cars when they work in Stratified charge mode.
After cleaning the spark plugs, I noticed a first difference – the popcorn became much, much quieter! Loud noises from the exhaust – completely gone! Now popcorn (again) was more like a hollow bubbling, not an explosion of the firecracker.
A second difference – the performance of the engine has become much smoother!
But, to avoid just a subjective opinion, I offer a comparison.
Ilde before cleaning the spark plugs:
And here – idle after cleaning the spark plugs:
The “teeth” have become smaller!
In this image: very low required torque (gear 6; around 90 km/h, reading of the econometer: around 3l/100km.
The engine works evenly! Why am I putting accent exactly to this mode? Here, I described the struggle with the uneven performance in this mode of very low required torque. And, what is interesting – that time, too, I performed the cleaning of the spark plugs, but at that time, this procedure did not help. That time, only the replacement of the spark plugs helped. This time, the spark plug cleaning procedure was efficient (at least initially). Obviously:
a. that time, the spark plugs were worn out (they had increased air gap);
b. this time, the spark plugs were covered with carbon.
It should be added – exactly the loud popcorn seems to be the best indicator of the sparkplug problems. Unfortunately, if there is a stock exhaust, this indicator is missing, too,
In the last step, I checked the detected fuel quality for the last refuelings. Maybe the poor quality fuel “made a point”? As we see, there were no troubles with the fuel (in the DME understanding):
And this is the overall statistics. The record regarding one average quality refueling was already when purchasing the car. So, I have refueled it with only high-quality fuel.
Unfortunately, DME determines only the approximate fuel octane number (evaluating the readings of the knock sensors). DME does not “see” if the fuel contains/does not contain a large amount of sulfur, lead, or any other chemical content.
Taking into account the harsh situation with the spark plug problems of the B series engines, as a solution, I see – DME performs this spark plug cleaning program automatically; the interval of the procedures is adaptive and depends on the driving mode. I know that BMW AG employees are reading my blog. Guys, this would be a very useful feature! A huge thanks in advance in the name of all BMW users!
Yesterday, I specifically checked TIS – still not a word regarding the spark plug change intervals. I predict that the problems caused by misfires will be in the stable first place between B series engine users!
I have to add that my delight regarding the smooth performance of the engine wasn’t long…