Opinion about spark plug condition

[DaniTD]

Today, I decided to put the now-BMW-recommended spark plugs for the M40 (NGK BKR6EQUP) and put a new set of BOSCH F8LCR (the originals with a resistor of only 1kOhm).
The thing is, the 4 spark plugs were on the same condition, but I am not able to make a correct evaluation of them. Although they are clean on the electrodes, the base is somewhat sooty with black sludge.



The thing is that from a long time ago I had a lean condition (CO 0,1%) mixed with a high HHC (550ppm).
I decided to change the plugs because after studying them, the NGK's had too much resistance and too wide gap.
Maybe because of this I had a lean condition and the improperly burned fuel made that soot and the exhaust smell a lot like raw gasoline?

What are your thoughts?

Thank you!

[Speedtouch]

They look like a poor design, with the centre electrode recessed to the level of the ceramic insulator - normal spark plugs have the centre electrode protruding by approx. 1mm or so.

[BenHar]

The wiki says use NGK BPR6ES.

http://www.e30zone.net/e30zonewiki/inde ... park_Plugs

Pretty sure these multi electrode things don't work well in e30 engines.

Ben

[DaniTD]

About poor design... can't say. They are the same BMW recommends for a S62...
I know the recommended ones by the wiki are the NGK's but I got the original ones to try, the thing is what the old spark plugs can say about the running condition of the engine.
Thank you

[DaniTD]

Pretty sure these multi electrode things don't work well in e30 engines.

As on its big brother, the M70

[BenHar]

They look as though they've done a lot of miles. It's not easy to tell with old plugs.

Put new ones in, do a few miles and then have a look.

Ben

[Brianmoooore]

These are the plugs BMW recommend for the M40 these days. The recessed centre electrode is so that the spark slides over the insulator, which is supposed to stop sooty deposits building up on it, and the four electrodes are basically to extend service life. The spark will always jump to the closest one, so as that one wears away, another will become closest, the spark will switch to that one, and so on.

[Carmo13]

I would say your spark plugs look fine, the electrodes are light tan/grey colour, which I have always been told is a sign of clean combustion.

[HairyScreech]

These are the plugs BMW recommend for the M40 these days. The recessed centre electrode is so that the spark slides over the insulator, which is supposed to stop sooty deposits building up on it, and the four electrodes are basically to extend service life. The spark will always jump to the closest one, so as that one wears away, another will become closest, the spark will switch to that one, and so on.

Yep, all of the above, While providing significant impediment to the spreading of the flame kernel.

Multi electrode plugs are

[DaniTD]

The thing is, before replacing the plugs, it was impossible to get a rich running condition on this engine. Now, after replacing the 4 electrode ones with the original F8LCR's, engine started to run rich. When cold and pumping the brake pedal, the RPM's went up and when hot, the engine barely notices the brake pumping (I believe it's normal in cold because, when cold the engine runs more rich and when depressing the brake pedal you pump a squirt of air to the engine, thus the RPM go up for a second).
Tried to adjust an old AFM to play with the mixture, with the old plugs enrichening or leaning adjusting the spring tension didn't make much difference. Now if I richen it the idle starts to jump between 500 and 1500 rpm. Leaned it to the point the idle is stable, now the engine has much less hesitation and the engine doesn't bog down when blipping the accelerator, and the transition when applying gas at changing gears is a lot more smooth