This entry continues the topic of the uneven performance of B58.

Symptoms: in a range of low RPM (below 2000, more noticeable by 1000 .. 1500) by the minimum required torque, the uneven performance of the engine can be felt. Symptoms are progressing; during the time, also idle become “restless”.

15.000 km ago, the spark plugs of the engine were replaced – initially, it solved this problem. In addition, no analogs, not OE, but original BMW spark plugs, purchased at the BMW dealer center were installed – both electrodes (also the side one) of these spark plugs are made from precious metal. The resource of such spark plug type in the catalogs is indicated quite impressive – for 100.000 km. The resource of the spark plugs should be measured in cycles (or in the worst case – motor hours), and that will be shorter in city traffic, but in any case – the life span of 10 .. 15.000 km can not be the “end” of the spark plugs.

Obviously, the problem hides somewhere else. 

Considering that the car still has a warranty, I got in touch with a dealer. Petrol engines (not even talking about B58) is a rarity in our area; I was not surprised that the dealer center specialists haven’t heard of such a problem. The head of the dealer center offered diagnostics for EUR 80 .. 160, during which the DME error messages will be red. I objected that there were no error messages in the DME. This fact confused the head of the dealer center. Well, then they don’t have any idea; they can open a “case” and ask for advice from the BMW specialists. 

I hoped that BMW had released the software update (last time the Integration of the car was upgraded two years ago), but the dealer center specialist saddened me: there are no updates to the DME software!

In short, I will mention the main DME software problems (which relates to the uneven performance of the engine): 

a. in EDIABAS Call-up function list, misfires are not reported at all; 

b. at the moment of shifting gears (if the car has a manual transmission), the misfire registration is not blocked – misfires are regularly registered at the moment of switching gears without justification;

c. the misfire registration threshold is fixed (and high), so the misfires are not registered in a range of low required torque.

So, in the question of misfires, the dealer is quite helpless (to identify misfires at all, the test drive with connected iCOM and activated Expert mode should be performed).

From all previously mentioned, I understood that this time the dealer would not be the one who could help me with solving this problem. 

If the dealer is not a solution, I have to solve the problem by myself!

At the first step, I checked the misfires counters via OBD Mode 6.

Note: B58 misfire counters are displayed vice versa (comparing to N53/54/55 etc.) – at first: intersession counters, only after – misfire counter of last driving session.

As we see, the long-term counters are 6/5/7/5/5/6. Yes, as I already mentioned before, if the car is equipped with a manual transmission, random cylinder misfire events are recorded every time the gear is switched. But what is essential from these data – misfire counters in all cylinders are pretty similar. It means – obviously, precisely, the “fake” gear switching misfires dominate; no additional/other misfires dominate in any cylinder. How so? What could happen to all these cylinders?

I checked Rough run data in Expert mode during the actual driving sessions. Yes, really, uneven performance is typical for all cylinders!

Incorrect fuel mixture? I checked: Lambda around 1.0 – everything is in order! 

Incorrect injection timing? I would not be surprised, but then there should be a “louder scream”, at least on the Internet. 

I checked once again, or yet DME misses some misfire in a problematic mode. To perform it:

a. I chose a longer stretch of road, where I can drive with speed 60 .. 80 km/h;

b. reached 80 km/h, switched gear 6;

c. performed fixation of the misfire counter data in OBD mode 6;

d. I drove in the problematic mode, not switching gears;

e. after a specific time, I repeatedly fixed misfire counter data;

f. I compared the indication before and after the driving session.

No, 0 registered misfire events even during a longer time! In DME understanding – everything was fine.

What could happen to all cylinders? Problems with injectors? Damaged ignition coils? Does not sound credible. Problems with spark plugs?

The only credible reason, what I could imagine – problems with spark plugs. What could have happened with them?

Here, a typical “view” on power and torque displays, driving with speed around 90 km/h:

As we see, the required torque is around 50 .. 60 Nm, which means, slightly above 10% of maximum, the power instead – only several % of maximum. It is clear that in this mode, the spark plugs are working in a normal mode.

Short derogation: one of the basic parameters of the spark plugs is heat number (heat range). Here, you will find basic info.  

My version regarding causes of the problem – due to inadequately “gentle” driving mode, the spark plugs don’t reach the self-cleaning temperature, the carbon residues on the insulation are formed, and the performance of the spark plugs gets worse. Lately, the COVID pandemic rages in Europe, and during 10’000 km, I did have the option to drive in a more “correct” mode. 50/90 km/h speed limits and driving in a stream with a compact class sars is not the “most convenient” driving mode for B58. The version has a basis!

During the last holidays, I had the option to check this version. For half an hour, I had a chance to drive more aggressively, with an average speed of 120 km/h.

Yes, after this drive, the problem was significantly reduced! Obviously, the cause of the problem truly is a too low work temperature!

In several Internet forums of BMW fans, the discussions regarding “colder” spark plugs can be found – they are used after different “upgrades” of B58 (power increase). This time (due to smooth driving), exactly “hotter” spark plugs could be helpful. Unfortunately, BMW itself does not offer different versions of spark plugs for different driving modes. Obviously – the only solution is: use B58 in the appropriate driving mode.