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  #1  
Old November 25th, 2006, 20:12
hudsxj hudsxj is offline
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No spark plug gap?

My grandads 2001 xj was misfiring and throwing the MIL. I had the codes read and it showed to have a random misfire on cylinders 3 and 6. So we replaced the plugs and found that those two did not have a gap at all due to something hitting them. I replaced all the plugs with champions and it was still missing somewhat, so I then replaced the coil pak and it was still missing this time on the number one cylinder. So I pulled the plug on #1 and the new plug now had the same problem that the old ones had in that something had hit it and it had no gap anymore. The next thing that I did (though it may have not been the right thing was) take the head off and check for anything in the pistons, the only thing that was found was a few small chunks of carbon, it has 104xxx on it all by my grandad mostly city and highway driving. Any ideas? Do I need to go ahead and rebuild the head while it is off? Anywho thanks for the help.
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  #2  
Old November 25th, 2006, 20:27
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: No spark plug gap?

I think someone has put the wrong plugs in that engine, that are too long and the pistons are hitting the electodes......
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  #3  
Old November 25th, 2006, 21:12
hudsxj hudsxj is offline
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Re: No spark plug gap?

I don't think that that is the problem, due to the fact that I had the problem before the new plugs were put in, and also it does not make any sense that if all of them were the same length that only one would have the gap closed on it? Also I do not have any marks on the pistons and it was not making any noises when it was running. Any other ideas?
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  #4  
Old November 25th, 2006, 22:02
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langer1 langer1 is offline
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Re: No spark plug gap?

The correct plug is RC12ECC is that what you have?
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  #5  
Old November 25th, 2006, 22:13
hudsxj hudsxj is offline
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Re: No spark plug gap?

yes those are the ones that I have, I am beginning to think that maybe the chunks of carbon hit the plugs just right and knocked the gaps closed. Its kinda stumping me though...
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  #6  
Old November 25th, 2006, 22:24
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langer1 langer1 is offline
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Re: No spark plug gap?

2001 heads were prone to crack, so have them check for that at least.
Any cylinders/pistons that are cleaner then the others could be the ones that have a small leak.
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  #7  
Old November 26th, 2006, 07:26
hudsxj hudsxj is offline
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Re: No spark plug gap?

so do ya'll think that I can get away with just having the head rebuilt or do I need to pull apart the whole engine? I am just trying to make sure that my grandad has a reliable car as he does not live locally. Thanks
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  #8  
Old November 26th, 2006, 07:41
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Re: No spark plug gap?

I've just never seen the electrode gap physically pushed closed before. Except on a interference motor that lost a timing belt. Were all the plugs physically the same size ? I know when I bought plugs once, 4 from my dealer on a friday and cleaned him out and 2 from a parts store on the way home the OEM and the parts store had the same number on them but the dealer plugs were beefier, had a thicker electrode then the parts store ones, same plug number just different plugs.
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  #9  
Old November 26th, 2006, 13:38
hudsxj hudsxj is offline
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Re: No spark plug gap?

They are all the same size as near as I can tell, this whole thing is just really weird to me, I don't really understand whats wrong with the silly thing and its driving me up the wall.
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  #10  
Old November 26th, 2006, 13:57
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8Mud 8Mud is offline
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Re: No spark plug gap?

Double check your plugs, that they are exactly what the book recommends. The letter designator after the number is important, could be the difference between washer plugs and cone plugs, which will make a difference in how deep they seat.
I've seen guys put in quite a bit longer (hotter) plugs and not have clearance problems, though they caused other prblems, like detonation, scortched spots on the pistons and wore out fast.
If the connecting rod bearings are excessively loose, they are likely really noisy. Run a piston to the top, use a piece of welding rod bolted to a handy spot as a makshift dial gauge. Have someone rotate the crank (from the front harmonic balancer) you can see how much pop up and/or timing chain backlash you have. If there is s significant difference between two cylinders, that is surely someplace ot start looking (front main bearing?). Though without an awfull lot of knocking I really can't see a piston coming up high enough to contact a plug.
Detonation, can cause deformed plugs.
You may want to try a set of one colder plugs, especially if you live in the hills, and/or do a lot of high speed driving. Also premium gas. Near full open throttle, high speed, on a mild up slope, can be a motor killer, motor can run way lean.
If a plug gets too near a piston, you can often see a burn pit and/or scortch marks.
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  #11  
Old November 26th, 2006, 16:28
Tom R. Tom R. is offline
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Re: No spark plug gap?

I had this happen on my XJ before. Pulled the plug nearest the firewall and saw that the electrode was pushed closed. It hasn't happened since, but I can assure the correct plugs were used.
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  #12  
Old November 26th, 2006, 19:45
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Re: No spark plug gap?

if you have the type that have the washer and you put the washer on wrong this could happen and you would not hear it unless you had a screw driver positioned just right on the head when you started it. But now if you had dome pistons instead of flat tops and did not index the plug to fit the dome then this could happen. If you have the head off then screw in the plug and tighten it down then take a flat edge and see how much of a gap you have between the edge and the plug also do the same for the piston move it to top dead center and straight edge it useing a fealer gauge to measure with. Good Luck
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  #13  
Old November 26th, 2006, 19:58
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Blaine B. Blaine B. is offline
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Re: No spark plug gap?

Sure you aren't just putting the plugs in and pushing the gap closed on the area around the spark plug hole?

Like hitting the tips on the cast around there......

I did that to one of my plugs once.
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  #14  
Old November 26th, 2006, 20:02
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Re: No spark plug gap?

Quote:
Originally Posted by Blaine B.
Sure you aren't just putting the plugs in and pushing the gap closed on the area around the spark plug hole?

Like hitting the tips on the cast around there......

I did that to one of my plugs once.
It would take some force to do that. Hopefully he is careful when he is replacing them.
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  #15  
Old November 26th, 2006, 20:13
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Blaine B. Blaine B. is offline
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Re: No spark plug gap?

Well, that happened to me for the front plug....kind of hard to get to with bare hands, so I just put it in the plug socket and pushed it in.......dumb to do, always use your hands to start them, no matter what you have to wedge aside.
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