spark plugs shorting out mystery

[friendly_jacek]

In the boating section I posted a long winded story how I couldn't start my boat yesterday. Turned out 3 of 4 NGK plugs were shorted and the engine got flooded. I replaced the plugs with old OEM AC ones and the engine started. Now is the interesting story. I let the plugs dry overnight and their resistance measurements between the electrodes are: 3 MOhm, 13 MOhm, 100 MOhm, and infinity (this is the only one that didn't short).

I washed them in solvents, dried, and got exacrly the same results. Seems permanent failure. The plugs are in good shape, not oiled, carboned, etc. Some superficial corrosion on the outside coating though. They worked fine when boat was put to storage 2 years ago.

I searched the internet and some people swear that if a plug is flooded once, it's not good anymore. I found it difficult to believe, but my story seems to confirm that.
Now, plugs are cheap, so these will go in trash, but why is it?

This is the only explanation I could find:
http://www.gsparkplug.com/shop/fouling-shortingout-problem-modern-plugs-champion-vs-ngk/

 

[yvon_la]

might be related to the fact sparkplugs have resistance included in them now a day,might be blowable or breakable

 

[Chris142]

was any antisieze used?

 

[spasm3]

Originally Posted By: Chris142
was any antisieze used?


Ive had that happen to me. got the tiniest bit on the center porcelain and it skipped like crazy. Could not clean it off only replace.

 

[friendly_jacek]

No antisieze on those. They go out and in every winterizing, iron block, so I felt no need for antisieze.

 

[JimPghPA]

I wonder if the ceramic around the center electrode might be porous enough to allow gasoline to enter, and if so maybe placing those plugh in an oven set to something like 400 Fahrenheit for a half hour or so might cause any fluid inside of the porous ceramic to boil off.

 

[Gokhan]

Originally Posted By: yvon_la
might be related to the fact sparkplugs have resistance included in them now a day,might be blowable or breakable

That's just a 5 kiloohm resistor in series with the center electrode. That has nothing to do with the resistance measured between the two electrodes, which is a resistance in parallel.

 

[Gokhan]

Originally Posted By: friendly_jacek
I let the plugs dry overnight and their resistance measurements between the electrodes are: 3 MOhm, 13 MOhm, 100 MOhm, and infinity (this is the only one that didn't short).

I washed them in solvents, dried, and got exacrly the same results. Seems permanent failure. The plugs are in good shape, not oiled, carboned, etc. Some superficial corrosion on the outside coating though. They worked fine when boat was put to storage 2 years ago.

I searched the internet and some people swear that if a plug is flooded once, it's not good anymore. I found it difficult to believe, but my story seems to confirm that.
Now, plugs are cheap, so these will go in trash, but why is it?

This is the only explanation I could find:
http://www.gsparkplug.com/shop/fouling-shortingout-problem-modern-plugs-champion-vs-ngk/

You don't touch the metal parts of the ohmmeter terminals when you measure it, do you? If you do, the resistance of your body will go in parallel and give you a finite resistance reading.

Otherwise, the only way you can get finite readings would be some carbon or oil deposits that went deep and can't be cleaned. Give your engine a slightly open throttle while you start it until it starts running smoothly so that it doesn't get flooded.

 

[friendly_jacek]

Originally Posted By: Gokhan

You don't touch the metal parts of the ohmmeter terminals when you measure it, do you? If you do, the resistance of your body will go in parallel and give you a finite resistance reading.


I'm careful not to do it. My skin between both hands measures about 2 MOhms. I measured several times and got the same results.
I will stick them in the oven just for fun, but I'm picking up new plugs tomorrow. I have to have 2 sets of good plugs.

 

[jrustles]

Clean them of grease and drop them in some vinegar for a day. I reconditioned some sweet factory ACDelco "NGK Iridium laser" plugs (made in USA of Japaneses parts) a week ago. It turned out well, the iridium electrode tips are bright and shiny, the platinum puck on the ground electrode is too. Both electrodes are there after 100K miles, so plugs were re-gapped and ready to go!

 

[friendly_jacek]

Vinegar? Sounds like a good idea. Why not? Nothing to lose.

 

[friendly_jacek]

NGK says you can't always clean their plugs once they are fouled. I think this is what happened.

Quote:
Fuel, oil and carbon fouling can all be the result of different causes but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly. In many cases, the spark plug cannot be cleaned sufficiently to restore normal operation. Therefore, it is recommended that a plug be replaced once it is fouled.


http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqfouled.asp?mode=nml

 

[jrustles]

Originally Posted By: friendly_jacek
Vinegar? Sounds like a good idea. Why not? Nothing to lose.


Yes any weak carboxylic acid will be strong enough to clean them up without wearing/etching. OTo clean platinum and iridium plugs, I keep them away from sandblasting, and have my doubts about air blasting, which is just sandblasting without the sand

NGK is right, despite not going into more details. If an old plug is physically damaged in any way, it must be replaced, that's true. The set of OEM Delcos mentioned prior were in prime condition!

 

[friendly_jacek]

I tried 10% vinegar last night, but aborted in 10-15 minutes when I noticed significant gas bubbling coming of the threaded shell. I was quite surprised, maybe NGK used Zinc coating?

 

[SteveSRT8]

Time to add garlic and seasoning and make pickles!

Note that 10% acetic acid would be quite strong!

 

[jrustles]

lol ^


don't be afraid, bubbling, gassing and etching is a good thing!
while I only used 5% from the kitchen & left them for 24hours, 10% is better. The key is to get them dry of all grease/oil, oxidation and ash is what the acid will take care of.

Here's an OEM ACDelco, which is really just a USA assembled NGK Laser Iridium after a casual cleanup

and another pic with a different white balance for good measure

Tough to tell that they're 100K mile(160K KM) - 9 year old plugs

Originally Posted By: friendly_jacek
I tried 10% vinegar last night, but aborted in 10-15 minutes when I noticed significant gas bubbling coming of the threaded shell. I was quite surprised, maybe NGK used Zinc coating?

 

[friendly_jacek]

Originally Posted By: jrustles

Tough to tell that they're 100K mile(160K KM) - 9 year old plugs

Indeed.
These are the OEM laser iridium from my corolla at 75000 miles. More wear than yours. I blame it on city driving.

 

[friendly_jacek]

Update:
It's no longer a mystery. Following some online advice, I applied oven cleaner overnight, rinsed in water (lots of brown-gray goo came from the bottoms of the insulator wells; this is the part that surprised me), and dried in kitchen oven. That brought them back to life and infinity resistance between electrodes.

 

[Rick in PA]

That oven cleaner trick sounds like a winner. Thanks.

I have burnt the carbon off lawn & garden plugs using a torch, but only in a pinch. I'd set the plug on the bench vice and apply the flame of a propane torch on the tip until everything glows. It burns off all the garbage, but it is tough on the plug.

I work with high voltage / low current at work. Any resistance you can measure with a standard VOM would kill something like a spark plug.

Next time I've got a little gathering of lawn & garden fouled plugs, I'll try the oven cleaner trick.

 

[Gokhan]

As I said earlier, opening the throttle valve slightly while cranking and keeping it slightly open until the engine starts running smoothly should help prevent flooding and related spark-plug fouling.