N55 Spark Plugs changed (round 2)

[kleach18]

I decided it was time to change out the stock plugs after going through the mess with my last attempt..

http://www.1addicts.com/forums/showthread.php?t=885210

After doing some more research and running on the stock plugs for a few more thousand miles, I started to get random misfires under high boost. When I wouldn't get a code I could feel the car stumble sometimes while accelerating.

I went ahead and went with the NGK's 5992 plugs that are one step colder. Everywhere I read said that for high boost applications I needed to run a gap of 0.56mm. For stock to lightly modified cars we should run 0.70mm(stock gap of OEM plugs). Since all I had was a blade type valve clearance tool(looked everywhere here in Germany for a spark plug gap tool with no luck) I set it to a even 0.60mm.

Outcome: The car runs like it did when I picked it up from the dealership when new!!

It feels like it has better control under boost now. No more hiccups at idle, and pulls stronger(but dyno).

After I buttoned everything up I went ahead and measured the gap for the old plugs for shits and giggles. What I found was interesting..

Cylinders are numbered 1 being the front to 6 being the back towards the transmission.

Cylinder 1 plug gap=0.76mm
Cylinder 2 plug gap=0.76mm
Cylinder 3 plug gap=0.77mm
Cylinder 4 plug gap=0.81mm according to JB4 this was the one misfiring most if the time
Cylinder 5 plug gap=0.78mm
Cylinder 6 plug gap=0.77mm

So if these had the correct gaps from the factory of 0.70mm then the gaps increased a lot(in my opinion) in the 21,000 tuned miles that I drove on them. Seems like the center electrode gets worn out fast(understandably) in a car with FBO that runs e30 to e45 regularly.

Anyone have a comment as to why some are worn more then others?

In my rotary days I noticed that the rear rotors spark plugs wore out faster then the front bc the rear rotor seemed to run a bit more hot then the front. I wonder if the cooling isn't as great in the middle cylinders of the N55 and that's the reason for them wearing out a little bit faster.. Maybe I'm just over thinking it....

[Freon]

Originally Posted by kleach18

Anyone have a comment as to why some are worn more then others?

I'm not sure you will get any really satisfactory answer to this problem. Those differences are very slight. I don't think you can do much about it.

We could speculate. Each cylinder has slightly different cooling. Slightly difference injector flow (as much as coding and whatnot tries to eliminate flow differences). The intake and exhaust manifolds are not going to flow perfectly evenly to each cylinder. The car does not have EGT or O2 sensors for each cylinder. Each cylinder will have a different amount of carbon build up, thus not flow equally. So each cylinder might be slightly richer or leaner than the others. The car can really only make sure your average AFR is right, not for each cylinder.

The N54 guys have issues with plug wear once tuned up as well. I would suggest if you are not stock and running any extra boost that you regap every 15k and replace every 30k. It's just part of the tuning game! Pay to play.

[kleach18]

I have no problem replacing the plugs every 20,000 to 25,000 miles. In my RX7 I would change them every 10,000 to 15,000 miles bc it made a huge difference in performance.

I figured the difference in the gaps wasn't a sign of a problem but just a difference in the burn/fire rate of each cylinder. This is my first direct injection motor so I enjoy learning.

[MightyMouseTech]

I bought a PPK2 for my car. With the kit comes a sticker to change the spark plugs every 45000 km, or 28000 miles. And that is with an increase to only 320 hp.