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Discussion Starter · #1 ·
Gas Household hardware Auto part Metal Electric blue

Should I replace my spark plugs? Also since I have bad gas milage, I suspect I may be running rich does this photo tell anything about it?
What about wires? I know the wires have been replaced before since they are red (but now covered in whatever that black stuff is that you always get on your hands). They don't look bad or anything, but I don't know when they were replaced. Possibly when the spark plugs were new.
 

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https://www.hemmings.com/stories/article/reading-spark-plugs-2 Theres a great pic in here comparing sparkplugs and how to read them.

If you are already in there and they haven't been replaced in a long time (years) or if you know how many miles and its a lot, I'd replace them.

What model vehicle?
What motor?
What kind of plug is that?
 

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Discussion Starter · #3 ·
It's a 1991 Cherokee Xj with a 4.0 engine. The plug is a champion rc12YC. I'm pretty sure it's a normal copper plug. I don't know when they were last replaced, so I thought I could tell if they need replacing based on the photo.
 

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If you don't know, then something cheap like a plug is worth replacing no matter what it looks like. Don't forget to put some neversieze on the threads before installation. Either you or the next guy will thank you.

Regular coppers are the best plugs for the 4.0l. IMO, thats a dirty plug that needs replacing. The info I linked in my first reply will help tell you WHY it looks like that. Replacing the plugs doesn't fix the root problem(s) of why its running the way it is. If its rich or lean, look into O2 sensors, destroyed (cracked or broken) plugs obviously need replaced as they are their own issue, and the ash-fouled ones similar in color to yours (IMO) are from blow-by and burning oil. This can indicate some wear in the engine, possibly small enough to live with, that you [would now be] aware of.
 

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Discussion Starter · #5 ·
I suspect that the spark plug wires were replaced at the same time as those spark plugs, but I'm not entirely sure. They look fine with no cracking or wear other than the dirt and grime on the outside of the wire. Should I replace them, and are there other ways to tell?
 

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You're on your own there bud, none of my vehicles have wires lol.

Anybody else gonna chime in?
 

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My take on wired is unless it is some type of performance engine, they either conduct electricity or they don't
 

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Open your hood at night and rev up the engine, Any sparks coming from the wires indicate bad wires. But wires are cheap, and I replace them regardless when I change plugs.
 

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Not really. As long as they have similar resistance then you are good to go. Is your Jeep lifted? Gear ratio and tire size? Inflation pressure?
 

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Discussion Starter · #11 ·
Not really. As long as they have similar resistance then you are good to go. Is your Jeep lifted? Gear ratio and tire size? Inflation pressure?
It is not lifted, and I have stock tires. If my tire gauge is accurate, the tires have 25-28 psi in them. That's too low, isn't it...
 

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About 32 should do it
 

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View attachment 229957
Should I replace my spark plugs? Also since I have bad gas milage, I suspect I may be running rich does this photo tell anything about it?
What about wires? I know the wires have been replaced before since they are red (but now covered in whatever that black stuff is that you always get on your hands). They don't look bad or anything, but I don't know when they were replaced. Possibly when the spark plugs were new.
 

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Oh, I've seen this before. I thought it was just a normal copper plug. Looks like it has already been changed. But to be sure you should bring it to a mechanic to check.
 
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