Thank you to Jan for information and pictures. Some nuances seemed him quite suspicious, when replacing the spark plugs – and not without the reason. But Jan has acted conscientiously – the spark plugs were chosen from recommended in the official catalog – no free thinking or interpretation. What could go wrong?


But, about everything in order.

In the first part of this theme I assert, that for N43/N53 series engines only one model of spark plugs is intended: NGK ZKBR7A-HTU


But quite often there were (and still are) engines, which performed very unsatisfactory. The injectors, spark plugs, ignition coils etc. were replaced, and… They could not be used in Stratified charge! Shivering, group misfires – the cars just “lived” in service, to drive for a little while, and the repair specialists would conduct – after another repair nothing has changed and enhanced.

In all these case I found out, that for all these cars the Bosch spark plugs were installed; after replacing them with NGK – the engines suddenly “repaired”.


And here, images sent by Jan – in which the spark plugs of NGK and Bosch (as if analog 1:1, if we can trust seller – manufacturer) are compared:

Bosch spark plug – on the left side; NGK spark plug – on the right side.

Pay attention to the air gap of the NGK spark plug! It’s huge! Yes, the spark plug is used, the central electrode – slightly worn out, but in any case – the air gap is impressive!

Bosch spark plug – on the top; NGK spark plug – on the bottom. Perfect picture: even model numbers of spark plugs are visible – no doubt about identification!

In this image, you can clearly see the NGK spark plug is “longer”. The difference is several mm! And also in this image, we can clearly see, that the air gap of NGK spark plug is significantly larger than for Bosch spark plug!

NGK spark plug – on the left side; Bosch spark plug – on the right side.

I think any comments are redundant! These are COMPLETELY different spark plugs! And again you can clearly see the huge difference of the air gap.

So look’s a new NGK ZKBR7A-HTU spark plug:

Air gap is significantly larger than the diameter of the central electrode (not as for Bosch spark plug – less than half of diameter of a central electrode)!

Here, the NGK spark plug is intended for Stratified charge, but Bosch spark plug – only for engines with Homogeneous mode. In addition, the placement and diameter of the central electrode – also these parameters are fundamentally different. In case of NGK – regardless of which side electrode will “work”, the full power of the spark plug will be also in the center of the spark plug, and the fuel jet, injected by an injector, will be ignited equally well. Instead, in case of Bosch spark plug – depending on which side electrode will “work’, 3 different sparks can be – each in the separate part of the “space”. Depending on which electrode will be in use, the fuel will either get ignited (if the spark will be on the “closest” side to the injector) or – will not get ignited (if the electrode, further from the injector, will “work”). Of course, the small air gap will also cause problems – the spark will be to “weak”.


How could it be possible, that the huge number of BMW owners have chosen the inappropriate spark plugs?

The answer is very simple: Bosch has placed incorrect information in their official catalog!


You can check it by yourself:

For example, choose E60 car with N53B30 series engine:

An here – the result! The exact Bosch spark plug would fit!


Let’s check more detailed information:

Here, we see: the air gap is 0.9 mm! For the engines with Stratified charge, the air gap should be around 2 times larger! Also the diameter of the central electrode in incorrect – it has to be much smaller (the electrode has to be thinner).


First conclusion: that analog (only one), indicated in Bosch catalog, CAN NOT be used in N3/N53 series engines!


But, let’s see, what NGK say’s about their spark plugs. Here, the fragment of the catalog for year 2016/2017:

What, please? These spark plugs with an increased air gap can be used also in N52 series engines? In the engines, in which a “regular” spark plugs are installed? Don’t even talking about mistakenly indicated air gap (0.8 mm)…


Let’s check to match according to Realoem data:

As we see, N52 series engines are not listed. And that is logical – “regular” spark plugs are not compatible with these ZKBR7A-HTU High Energy spark plugs, not even looking at other differences (size, temperature mode, etc.). If you would install ZKBR7A-HTU in N52 series engines, the ignition coils will get damaged very quickly, the engine would have mass misfires!


Here, which spark plugs (according to Realoem data) are intended for N52N series engines:

And here, how do they look alike (they are completely in different size, with one side electrode):


Conclusion No.2: catalogs of BOTH leading manufactures (Bosch and NGK) contain coarse mistakes!

Conclusion No.3: obviously, you can rely ONLY on BMW databases!


And in the end: what are the consequences, if for N43 series engine “analog” spark plugs of Bosch are installed. Typical situation.

Here, misfire data after each (10 .. 15 minutes) test session:

Misfire counters of the actual driving session: 7/16/1/12. Accordingly – serious problems have appeared in cylinders No.1./2./4.

Long-term misfire counters: 2/2/0/1. Indications of these counters we can multiply with 10, to understand it easier. So, on average (during previous sessions) were around 20/20/0/10 points (events) in each session. If we keep in mind, that not all misfires are registered by the system, and not for all time full unit is added (usually: 0.X), we have to conclude, that during each driving session, the engine has shivered for hundreds of times!


After switching spark plugs to NGK. Test drive: 30 km.

As we see, all long term misfire counters are 0. So: during last(5 .. 10) sessions, the number of misfires is small – below 5 events in each.

Short-term counters: 1 event in the 1-st cylinder, in others – 0! Perfect result!


How to use misfire counters


In this case, we have to pay also attention to cylinder No.3 – even with Bosch spark plug, it has worked correctly (misfire counters – close to 0). Yes, it is very interesting. I assume, that the causes are the following:

a) the injector of this cylinder injects fuel with a bit wider bundle – the fuel “gets” closer to spark plug;

b) possibly, completely incorrect adaptations (thanks to a misfire of all cylinders) – the fuel mixture is significantly richer (in relation to other cylinders), so it ignites much better.