Eroded Spark plug?

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2001 Jeep Grand Cherokee 4.0 4x4 Started having a little misfire and hard starting, so I decided to pull the plugs. All were so eroded that they were at .055-.060, instead of the spec .035. Plug #4 looked like this: I guess this was a long time coming. Still have a bit of rough starting sometimes. Just put Gum out in the tank, and doing Chem tool through the intake tomorrow.
 
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Oct 23, 2005
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Originally Posted By: SuperDave456
That looks like its a platinum tipped plug. How many miles are in these plugs?
That's what I was going to ask....I've had a few 4.0s and that plug looks like it's been in there a long, long time. DoubleWasp, just stick with the cheapo Champion or NGK plugs (usually less than $2 each) and change every 30k. Mopar knew what it was doing recommending 30k plug changes in the 4.0.
 
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A genius Harley mechanic taught me a long time ago, change your plugs first before diagnosing anything else. It has been brilliant advice. I am thinking the plug failed. Other running problem can flow from that, and need time to correct with that cylinder firing correctly. You don't have to attribute it to wrong plugs, bad gas, injectors, etc. I throw all this out there because I question the OP on the background of the photo.?
 
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Jan 22, 2011
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Ohio
That's called ash fouling. It happens from burning oil.I had them actually bridge across the plug and short it out.
 
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Originally Posted By: Lubener
That's called ash fouling. It happens from burning oil.I had them actually bridge across the plug and short it out.
Ditto - the plugs in "Wonder the Thunder Pig" looked much worse to the point that like you, the deposits on some had actually filled the gap on the electrode. When I pulled them and saw what I saw, I was surprised they were firing at all.
 
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Perhaps the valve stem seals are leaking oil or bad rings if its on all cylinders. Looks like deposits from burning oil as others have stated.
 
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You got an oil burning cylinder. Look at all the oil on the plug threads as well. I bet the other plugs (if they aren't fouled like this) have threads that are much "dryer". In my K1500, Cylinder #1 has a plug that looks like this after 1000 miles. So as soon as it begin to miss a bit, I pull it out, clean it off with a wire wheel, and back in she goes. You might consider doing a piston soak in that cylinder and/or letting that engine ingest a gallon or two of hot water through the intake. The latter always amazes me at the results I get after I do it each time.
 
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Run an oil change with 1 bottle of marvel mystery oil, and walmart or autozone store brand(this stuff really cleans sludge) oil. Change it out before dip stick oil gets nasty when viewed on a white paper towel. Then continue using a good cleaning oil like walmart or autozone brand.
 

DoubleWasp

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Plugs are Champion Platinum. Mileage unknown. New plugs are Auto lite Single Platinum. I suspected oil burning as well, but honestly cannot find a source. It's not coming in through the PCV system, does not appear to have any oil consumption through rings or valves, and appears only on one side of the plug. I was ready to blame oil consumption through the intake tract, but while I have the throttle body off for cleaning, intake looked spotless on the inside. It's a weird one, and one I hope not to see again. I ran a bunch of B12 down the intake to clear out any nastiness that may remain. Power and fuel economy are up in a major way. This Jeep has a coil on plug ignition, so there are no wires to do here, but with 205k on the clock, I'm probably just going to go ahead and do injector replacement and a new coil pack anyway. I was expecting to see something bad in #3, which had recorded misfire on multiple occasions, but #4 turned out to be a real culprit.
 
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Originally Posted By: DoubleWasp
This Jeep has a coil on plug ignition, so there are no wires to do here, but with 205k on the clock, I'm probably just going to go ahead and do injector replacement and a new coil pack anyway.
I have heard about upgrading to multi-hole injectors on Jeep 4.0L engines. Is that your plan when your replace your injectors?
 
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