Spark plug fouling. Bad coil or cylinder problem?

[misha]

...found the one in the driver's side cylinder was destroyed....its ceramic was missing, and the cylinder hole was caked in brown...

Those remainings ended up in cylinders and maybe valves.
I would be susprised if that cyl.is not destroyed and warped seriously.
The problem you have is because the cyl.rings on that cyl.are damaged(or cyl. walls) and they leaking oil causig the spark plug to foul with oil.
Every time you install a new spark plug it is fine for a while...about a day...untill it is fouled up with oil again and misfiring begins again.

Check compression on that cyl.Im convinced that there isn't any.
If it still have compression...your engine is the luckiest one in the world.

[FireFox31]

I ran the test, preparing by removing the fuel pump relay and disconnecting each of the five coil packs. When I cranked the engine, the passenger cabin smelled a little like gas.

I don't trust my results because of the insufficient tester that I borrowed from AutoZone. I could only tighten the screw connector by torquing its rubber hose. I actually think the results were different when I had someone hold the tester compared to when it was propped on its case.

EDIT: These test results are entirely wrong because I forgot to hold the throttle wide open while cranking the engine.

I filmed the results so I could check the pressure at each crank. Here's what I saw:
Cr 1 2 3 4 5
#1 100 135 155 170 175 Resting on case
#2 100 140 150 170 175 Resting on case
#3 95 135 155 170 175 Resting on case
#4 105 145 170 185 190 Hand held
#5 105 150 170 185 190 Hand held

Cylinder #5 is the one that blew the spark plug and started fouling the new one rather quickly.

I'm going to buy a good tester with a long, metal extender to provide a good seal with the cylinder. Can anyone recommend a good one? Thanks.

[tryingbe]

Save your money on the gauge for a new engine.

Your engine is very worn and using oil.

[rguzz]

I'm guessing you can trust numbers like that because they are pretty similar and no real low ones. Not sure you need to buy another tool and repeat. Others about what to do next?

[erikv11]

I agree the close grouping of the numbers is good, but 170 is very low for an NA. The numbers suggest no one cylinder is bad (no bad valve or bad spot in the head gasket), but that all cylinders show wear. If the gauge is accurate, then as tryingbe said there is apparently a lot of blowby and oil consumption. If the gauge is accurate. Maybe get a gauge from a different parts store to save you the expense of buying one.

OP, does the car consume a lot of oil between changes, do you get tufts of blue smoke out the tailpipe?

If it is worn but runs fine, I'd keep driving it.

[FireFox31]

Oh no, I just realized that my test results are entirely flawed. I forgot to hold the throttle wide open while cranking the engine. I'll do the test again in a week.

I will also carefully monitor the engine oil level. I often drive 350 miles non-stop, so I should be able to see the oil being consumed after 1050 or 1400 miles.

Save your money on the gauge for a new engine.

This is my second engine. That's why I want to carefully diagnose and repair it. It has 200k miles on it, the most 100k of which were from me. Still, it runs smoothly, powerfully, and with seemingly good fuel economy (maximum 27 mpg highway).

Thanks for all your help. I'll check back late next week with pressure numbers from a correctly performed test.

[abscate]

Yeah, when you get low numbers all the way around, it is usually the test procedure. These engines bottom end is near bullet proof.

[FireFox31]

I repeated my compression test using the correct procedure with a good tester. These are the pressure results that I got for each of four cranks:

Cyl 1 2 3 4
1 120 160 181 191
2 120 162 186 196
3 120 162 186 195
4 130 170 191 205
5 128 170 190 200

Cylinder 5 is the one that's fouling its plug, yet its compression numbers are solid.

I've driven another thousand or so miles and the car runs fine, except for gentle random misfires at idle (and presumably while driving). What would cause the misfire if compression shows that the cylinder is not leaking?

[misha]

The fact that it fouls a plug with oil is indication that the cylinder is leaking oil.
Oil is passing by rings and fouls a spark plug.
That's why you have a misfire just on that cyl.

[scot850]

Could be a cracked ring. Had an issue on a 760 turbo that the dealer told me was a head gasket failure, but turned out to be a bad piston ring. Car otherwise ran ok.

Neil.