Spark Plugs -- Heavy load of light gray and black deposits

My CJ began running rough last week, and I pulled the plugs to see what the trouble was. I need new plugs, but it was running so poorly, I resorted to a "trail fix" to see if the valves were still intact. (the valves are fine, I think)

Anyway, the #3 and #4 plugs had heavy loads of build up on them. The 3 plug was black and the 4 plug was light gray, all of the other plugs were clean as a whistle. The build up on both plugs cleaned off easily, and the problem went away immediately when the cleaned plugs were put back in -- the essence of a Trail Fix is to take something off, have a beer, and put it back on then see if all is well with the universe again.

My question is, what does Light Gray, and Black mean as they relate to deposits on spark plugs? I'm thinking the black plug is telling me that a valve guide/seal is going/gone, but I'm not sure what the gray plug means. The build up was pretty large (it fouled the plugs to the point of them not working), but the mass was not that great. The stuff was pretty light and flaky, and came off with small knife. I probably could have removed the crap with my finger nail, or the cap from a beer bottle, if I had to.

Points of Interest I basically only use my Jeep to drive around town, and I use 3rd or 4th when I might still be able to use 2nd -- I tend to lug the motor is what I'm saying. I tend to time my stop sign approach for a minimal (if any) full stop, and then start out again in 3rd, then short-shift into 4th when I get to about 20ish.

I seldom get on the freeway, so my speed is generally below 50ish.

Unless wheeling in heavy sand, the power that I pour on is minimal, so I think I should be suing Cold Plugs as opposed to hot ones. These particular plugs were bought when I was doing more time on the freeway, and they may be a step hotter than the stock plugs. I'm thinking that I should go with the stock plugs when I replace them, or go with the one step colder on the range. Opinions? Why do I care about hot or cold plugs anyway?

Reply to
Jeff Strickland
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Jeff Strickland did pass the time by typing:

Black is an indication of fouling which can be as you suspect a leaky valve guide. Throw a vac gauge on the engine and watch what it does.

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It can also indicate too cool of a plug range, a bad sparkplug wire that results in a poor burn and excess buildup, or a leaky injector. How old are the wires?

Light grey is fine, that's usualy fuel deposits from additives. I like this site, good pics and writeups.

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Lugging will cause buildup. Sounds like you need to get out and give it a Ferrari tune-up. :)

Read this.

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The heat range you should use is the one that is indicated in your service book unless you have a special application. I have to run one range cooler to prevent detonation at higher comression levels.

Reply to
DougW

If you have the 258 engine, that can mean your wires are getting bad. 3 and 4 cross each other and can short together. If you use a spray mist of water in the dark when it is running, you can see if that is the trouble.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

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