Spark plugs - name that problem!

[NigelStu]

Swapping out my spark plugs during new-owner maintenance, and it looks like the PO didn't know the meaning of maintenance...

As I'm pulling the plugs, I notice that they are all dirty and worn with some carbon deposit - not surprised. Then I get to cyl 4. See the picture I attached.... All plugs had some deposit, oily wetness and severely worn, but 4 was exceptional. Electrode is basically coated in a hard coating, I could chip some of it off.

Side note, cap and rotor are also severely worn (and will be replaced), but post for cyl 4 isn't any worse than others.


I have some theories, but would like to see what everyone else has for ideas on what could make a spark plug look this bad.


I want to make sure I correct things that need to be corrected so that I have a top-notch engine again.


TIA

[caliGreen]

dang. Change all fuids! knowing the po. He probly didnt do an oil change for 10k+

[mr.vang]

there is no way that thing is giving out spark. lol

[lennon]

replace the plugs/do whatever maintenance needs to be done, then see if #4 is still getting like that. if so, rings, valve guides/seals. start fresh though before you decide it's a real problem.

[NigelStu]

No doubt on the lack of oil change; the PO failed. at life.

Oil change was the first thing done, and it was nasty! I'd guess more than 10k, the oil filter was even rusted! The oil in now will only be in for 500 miles; I'm trying to flush out all the old crap!

The car wasn't missing at all, so there must have been some spark making its way through all that crud! Albeit not a very strong one and likely not enough to get a complete burn; which could explain the signs of overly-rich running in the tail-pipe.




Would a leaking/sticking/clogged injector have impact on this? Or is this more of an oil issue?

Figured I could clean the injectors up since I'm already cleaning intake up and replacing fuel lines and other bits up there.

[NR-E30]

A leaking injector likely wouldn't cause that sort of build up on the spark plug. And flushing that oil is definitely a good idea, hopefully there wasn't any serious sludge build up.

[priapism]

Run some Seafoam through that thing.

[xwill112x]

from a tech stand point, looks like the electrode is worn, but not dead, and it has tons of carbon build up which likely points to the fact that the PO only used to car for short trips, never giving the plugs the time to burn the carbon off.

[NigelStu]

from a tech stand point, looks like the electrode is worn, but not dead, and it has tons of carbon build up which likely points to the fact that the PO only used to car for short trips, never giving the plugs the time to burn the carbon off.

Yes on the carbon buildup and the plug being worn. I was able to chip off some of the buildup off. BUT, it was only this plug that was so incredibly bad. The other 5 had some minor buildup and worn plugs, but nothing close to this one.


I put about 300 miles on the car between purchase and swapping plugs, including a nice little 100 mile HWY round trip with a bit of flogging and a 'benchmark' day where I put my data acquisition in the car and ran a bunch of 0-60 trials and a few 1/4 milers.

I did get the engine up into normal operating temps, so whatever the PO did as far as short trips, I should have cleared most of it out. Unless that plug was so fouled (and the rotor/cap too worn) that a decent spark never got through and that particular cylinder never got up to temp...


I'm still guessing some other issues.



Few updates:
-Injectors looked relatively clean w/o any buildup or gunk on the caps, and all work and are within correct resistance specs.
-valves were all equal, but a tad bit out of spec cold (0.011-.012 gap instead of 0.010 called out in Bentley)
-no visible signs of issues under the valve cover

[jlevie]

That looks to me like ash, which is the result of oil burning. I'd run a compression test (dry & wet) and a leak down test to assess the condition of the rings. If the rings are decent, the oil burning will be from worn valve guides and bad seals.