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Old June 25th, 2017, 11:57
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Carbon fouling, cleaning, limits of spark plugs?

Once a spark plug's ceramic is carbon fouled (say a new plug run way rich for 5 minutes and loaded with carbon) is the plug toast?

I cleaned mine, but its nearly impossible to get all the last traces of light carbon stain off the ceramic insulator. How much fouling can the ceramics take with carbon before they ground out the spark?

I used brake cleaner and Gumout carb cleaner, soaked them over night, and used a plastic brush and compressed air blow gun. Got them about 75-95% clean...but traces remain. Anyone have any experience with the limits on this???
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Old June 25th, 2017, 20:36
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: Carbon fouling, cleaning, limits of spark plugs?

After your thorough cleaning, the plugs are fine. A little staining
on the ceramic won't conduct enough (if any) to matter.

A good way to check a plug is to do a resistance test between the
terminal end and the electrode. The internal resistance on most
plugs is about 4-6K ohms. I've had (under load) misfires with
plugs that showed about 14K ohms. I've also had new out-of-
the-box plugs fail, so now I always check the resistance of any
plug before installation, whether new or used.
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Old June 25th, 2017, 21:13
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Re: Carbon fouling, cleaning, limits of spark plugs?

Thanks!!!! That is what I needed to know. Seems they can handle a lot of carbon fouling and still fire? Was trying to narrow down a super rich fouling problem....and needed to know if I could just keep cleaning the plugs while I sort out the real problem.

I have some Bosch jeep plugs I used for 10 years, with great results, fine platinum tip, that have infinite resistance using the ohm meter test. I thought they were bad when I pulled them and tested them recently, but they seem to be designed with a sealed internal air gap that is part of the plug design per Bosch. The new ones were the same. They worked great for 65,000 miles till two cyls started leaking oil too bad, bad valve guides.... That got me testing hotter and other plug designs...Now I have a massive running rich problem.

But thanks for clearing that what if up for me LOL


Quote:
Originally Posted by Runnin'OnEmpty View Post
After your thorough cleaning, the plugs are fine. A little staining
on the ceramic won't conduct enough (if any) to matter.


A good way to check a plug is to do a resistance test between the
terminal end and the electrode. The internal resistance on most
plugs is about 4-6K ohms. I've had (under load) misfires with
plugs that showed about 14K ohms. I've also had new out-of-
the-box plugs fail, so now I always check the resistance of any
plug before installation, whether new or used.
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old June 26th, 2017, 05:35
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Re: Carbon fouling, cleaning, limits of spark plugs?

I've run some really used up plugs with no issues, clean them, re-gap and run them some more.

You mentioned you have air. A pneumatic spark plug cleaner isn't very expensive, around twenty bucks. I have one I've been using for thirty years.

Low speed fouling is common and rarely causes many issues. Most times it burns off at highway speeds.

Seriously I always live by the mantra if it ain't broke don't fix it. I've neglected plug changes before just because the motor was running fine. And when I eventually did change to new plugs, the gap on the old plugs had grown a lot. I personally don't think plugs are all that critical if your ignition and fuel metering sensors are healthy. I worry more about the cables than the plugs, especially that coil to cap cable (Renix seems finicky about that one).
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Old June 26th, 2017, 09:32
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Re: Carbon fouling, cleaning, limits of spark plugs?

Thanks for the feed back, they will save me from wasting time and money on the wrong thing. I read warnings about how sand-abrasive can get stuck way up in the spark plug, and come loose later and score a cyl wall. I was already thinking of buying one, searched them and found that warning. I plan to revisit my MAP sensor hardware and see if the vac line got plugged. There is no way it should sit at 500 rpm at Idle and at WOT acting like I did nothing to the throttle!!!
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old June 26th, 2017, 18:26
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Re: Carbon fouling, cleaning, limits of spark plugs?

I find that burning the soot off of a fouled plug with a propane or butane microtorch works extremely well. I can usually cook the plug until the porcelain is clean. Just be careful if you use oxy/acetylene. (Melted a plug down once)
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Old June 26th, 2017, 18:33
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Re: Carbon fouling, cleaning, limits of spark plugs?

A gas stove works, a bit slow, but works too depending on fouled they are.

I bought a HF pneumatic spark plug cleaner for $9.99 today to play with too.

In the old days I would have used a boiling solution of caustic soda in an ultrasonic cleaner. I sold them back in the 70s.
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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