In this entry – concisely regarding the service procedure, which in ISTA is called:
Special procedure ”Cleaning and checking of ignition system”.
Cause of the problem: when driving with an inadequate low load for the engine, spark plugs are covered with carbon residues. The carbon residues interfere with the correct creation of the spark, so misfires appear even with very small wear of the spark plugs.
Solution: perform the spark plug cleaning procedure regularly in adverse driving conditions.
In which driving conditions do the misfires appear? For these engines, the most fragile are the following modes:
a. idle for the completely warmed-up engine;
b. very low required torque (slow braking with the engine – but not so slow for the Overrun mode to turn on);
c. transition modes (swifty changes of the required torque and/or RPM). In these conditions, the confirmation of the problem: loud (louder than usual/normal “popcorn”*.
* Remark: applies to vehicles with Performance and Sound kit installed; in Sport and Sport Plus modes.
Significant nuance: for these engines (in contradiction with technical literature of the BMW Ag), multi-ignition is NOT used (why – read here). Accordingly – if the misfire happens in any cylinder, the spark plug is not dried. Due to this reason, these engines are very sensitive to repeated/group misfires. So the problems can start in other working modes too, which are as “safe/stable” – one/two misfires in transition modes are enough.
In which cases does this procedure help?
This service procedure helps if there are no problems with the ignition coils (read more here) or the spark plugs (they are not worn out); if the engine has no problems with VANOS jitter (read more here).
How quickly do the spark plugs get contaminated?
My winter season driving profile includes at least 60% (by motor hours) driving outside residential areas with 80 .. 100 km/h speed. In such conditions, cleaning the BMW spark plugs (supplier: NGK) is necessary after each 4000 .. 5000 km. Subjectively, NGK/OEM spark plugs are contaminated faster, and the problem is more pronounced. Both spark plugs are visually very similar and hard to distinguish (but it does not mean that they are 1:1 like the ones sold by the BMW). I don’t recommend installing alternatives, for example, Champion spark plugs (read more here and here).
How to activate the cleaning procedure?
After identifying the vehicle and a complete test, open the tab: Power train/Engine electronics/Misfire detection.
From the menu, choose the 3rd option: Special procedure ”Cleaning and checking of ignition system”.
During the procedure, the engine RPM is increased to 2600.
Length of the procedure: 5 minutes.
After the procedure, the engine is switched off – it is normal.
Confirmation that the procedure was completed successfully.
Note: I perform the procedure mentioned twice in a row in case of strongly contaminated spark plugs.
