Think its time for a plug change...

[DustenA]

So, ever since I bought the car it had a miss under load, and occasionally under hard throttle. I was chasing vacuum leaks for a while and I got them all cleared up. Idle is good, drivability is good. But I noticed a random miss at idle and still under 2000 rpms occasionally.

Finally got a code for a miss, on cylinder 5, and then one for random misfire. Pulled the plug on 5 and found this beauty.


I have a spare coil I was going to swap, but the plug looks pretty suspect. My guess is during the vacuum leak the motor was leaning out and caused this.
Hopefully nothing major is damaged. I will stick my boroscope in the cylinder tomorrow when I do a plug change.

[auaq]

Usually a lean mixture would cause spark plug to run hot and appear as clean and white-ish in color. Your plug appears to have a bit of carbon build up and some mileage too. Either ways if plugs haven't been replaced in a while then change them now.

[DustenA]

Usually a lean mixture would cause spark plug to run hot and appear as clean and white-ish in color. Your plug appears to have a bit of carbon build up and some mileage too. Either ways if plugs haven't been replaced in a while then change them now.

The lean comment is referring to the damaged porcelain.

I've only put 3000 on them, but I don't know when they were installed.

[edjack]

Use only NGK BKR6EQUP plugs.

Is it a low-RPM miss?

[DustenA]

Use only NGK BKR6EQUP plugs.

Is it a low-RPM miss?

No. Well yes, but not only. It'll occasionally miss at idle. It'll miss occasionaly under 2000 rpm and heavy throttle, and yesterday when I got the CEL it was missing all through the rev range under hard throttle.

[geargrinder]

I could see hot combustion causing lean-damage, then 'running right' for a while darkening up the plug again...

The electrodes don't actually seem worn so it looks like the plug was pretty new, just suffered under abusive conditions?

In for the borescope pix. Hope you don't find anything.

[StephenVA]

How to"Read spark plugs"? https://www.ngksparkplugs.com/about-...d-a-spark-plug

it is like reading a snow fall. Top layer is last drive.

[DustenA]

I could see hot combustion causing lean-damage, then 'running right' for a while darkening up the plug again...

The electrodes don't actually seem worn so it looks like the plug was pretty new, just suffered under abusive conditions?

In for the borescope pix. Hope you don't find anything.

ya, im guessing abusive conditions, IE me ignoring the miss.

The piston in hole 5 was near tdc and looked okay through the plug hole. It'll be this weekend I think before I post pictures. I am working nights and don't feel like digging it out.

- - - Updated - - -

How to"Read spark plugs"? https://www.ngksparkplugs.com/about-...d-a-spark-plug

it is like reading a snow fall. Top layer is last drive.

I'm pretty good at reading plugs over all. When tuning my lightning we street tune it, and basically pull the truck over, install plugs, fire it up, make a pull, shut it down, read the plugs, adjust tune, install new plugs and go again. I was reading the damage on the plug, and the glazing, not the overall color of it.

- - - Updated - - -

Use only NGK BKR6EQUP plugs.

Is it a low-RPM miss?

Weird, the charts say the 97 runs a different plug

[StephenVA]

I am reading this on a iPad in Italy so there are no images shown. Plug damages are and weird colors are always from high temp swings, i.e. Lean conditions. As you are more then likely planning to, just screw in new ones and drive. Pull them in a few miles to inspect. Codes usually pop up before plug condition fails

[StephenVA]

1997 540 only plug?
BKR6EK.
http://www.partcat.com/ngk

[geargrinder]

https://www.ngk.de/fileadmin/Dokumen...en_code_en.pdf

EK vs EQUP...

K = 2 ground electrode
QUP = 4 ground electrode "semi-surface-discharge" platinum

So appears the existing ones are the K's.

Same dimensions, same heat range... I think BMW just upgraded the spec after 1997. I'd just go w/ the later platinum - my experience is they are excellent and last for ages in these motors.

[djb2]

That's not a worn plug.

Plugs really do last 100K miles.

Try swapping the coil, coil boot, and plug with another cylinder. Check both plugs after a few hours of operation.

[DustenA]

That's not a worn plug.

Plugs really do last 100K miles.

Try swapping the coil, coil boot, and plug with another cylinder. Check both plugs after a few hours of operation.

I didn't say worn. I said damaged. I'm not putting that plug back in any cylinder

I'll swap plugs. And I'll put on a known good coil and boot.

[DustenA]

Most the plugs showed sign of heat damage

[geargrinder]

Hows she running on the freshy plugs then?

[DustenA]

Hows she running on the freshy plugs then?

Seems normal. I couldn't get it to miss. I only drove it 10-15 miles. I'll know more Monday when I drive it to work. That's 60

[geargrinder]

Nice. Would be great to hear you're coming out of the "PO" woods.

[DustenA]

Nice. Would be great to hear you're coming out of the "PO" woods.

Nope. It's decided to pop the fuse on the drivers door twice in the last week. Need to see what can cause that

[Grim Reaper]

Interesting color mix on some of them.... could some of that be due to winter fuel blend issues / poor fuel quality?

[DustenA]

Interesting color mix on some of them.... could some of that be due to winter fuel blend issues / poor fuel quality?

It's possible.

[StephenVA]

Now that I cab actually see your images, You are right on the money as they appear to have had some overheat shock chips out of them, followed by normal short drives (rich then slow deposit burn off).
Your plan of action is spot on. Replace coil and plugs (suggested upgrade to single precious fine wire NGK recommended) drive and reinspect after 1K. Hwy driving will clean out the combustion chambers as well. Add a bottle of injector cleaner on next fill up.

Looking good!

[DustenA]

Now that I cab actually see your images, You are right on the money as they appear to have had some overheat shock chips out of them, followed by normal short drives (rich then slow deposit burn off).
Your plan of action is spot on. Replace coil and plugs (suggested upgrade to single precious fine wire NGK recommended) drive and reinspect after 1K. Hwy driving will clean out the combustion chambers as well. Add a bottle of injector cleaner on next fill up.

Looking good!

Well I've put almost 200 miles on the car on the new plugs. No misses, no issues, dash is showing almost 24mpg(its usually pretty close) so I have no complaints. I will pull them in a week or two and check them(I do almost 120 miles a day)

I installed these
NGK BKR6EQUP