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Old 19th December 2004, 11:36 AM   #1 (permalink)
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Gapping spark plugs?

My car has been struggling to start recently & it has now hit the point where it no longer wanted to play ball yesterday

After pulling all the plugs out (and finding they were literally black - think it might be running a bit rich lol) I cleaned them up & am not to sure about what to do with regapping them?

They are all pretty much identical with a clearance of .025. Is this an acceptable clearance?

I was going to close up the ones that are a little bigger than that but dont know whether to close these up a little too?

Im a similar note, they are NGK/Greddy Iridiums in it, what sort of life should I expect out of them
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Old 19th December 2004, 01:36 PM   #2 (permalink)
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Do you have the part code for the plugs. On NGK plugs the last part of the part code is the plug gap in mm which they are set to from the factory. Im sure it should be in the region of 1.1-1.3mm for iridium plugs, this would be more like 0.04-0.05 gap.

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Old 19th December 2004, 02:03 PM   #3 (permalink)
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I'll have a look for it...

Doesn;t help them looking like this though

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Old 19th December 2004, 03:22 PM   #4 (permalink)
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if all is standard the gap should be 1.1mm but was advised by shin to run iridiums at .8mm gap but mine is also running 1 bar of boost

Denso iridiums are good for about 20,000kms as stated by denso, but they are cheap anyway so change them every year
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Old 19th December 2004, 03:41 PM   #5 (permalink)
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You shouldn't gap iridium plugs. The coating is microns thick and you could damage it causing the plug to loose efficiency.
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Old 19th December 2004, 03:44 PM   #6 (permalink)
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C - For better burning to try and clear the soot problem on your plugs i'd go for a smaller gap like 0.8mm (0.032" if you like imperial). One thing to note here is with the very small centre electrode on this (your) type of plug is NEVER open up the gap by forcing a feeler blade into the gap as was common years ago on domestic stuff. If you need to close the gap tap it gently on a hard surface and measure til its right. To open a gap you need to bend the earth electrode carefully with a special tool or good pliers then tap back to reduce if necessary.
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Old 19th December 2004, 03:49 PM   #7 (permalink)
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Tony, they are already slightly smaller gapped than that?

I gave them all a good clean & brush, chucked them back in & wired the lot back up again (what a complete PITA job on a Skyline) & it appears to be ok now!

Even my missfire has sorted itself out, just gonna have to keep an eye on them as they have only done 3000 odd miles!
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Old 19th December 2004, 03:54 PM   #8 (permalink)
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Quote:
Originally Posted by R32 Combat
You shouldn't gap iridium plugs. The coating is microns thick and you could damage it causing the plug to loose efficiency.
yeah true they come pre gapped at .8mm which is what i used..ive know people break or bend the tips by doing so
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Old 19th December 2004, 04:01 PM   #9 (permalink)
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A smaller gap shouldnt be a problem really. Its the soot thats causing the misfire as it gets dirtier. It can be caused by the wrong grade plug (cant see the grade on the pic) ie too cold a plug wont self clean on a standard engine ie not enough heat in chamber to clean themselves. Another cause can also be a weak ignition system (amplifier?) or earthing strap to it. What state of tune is it? Better just add of course the most basic way of running too rich is blocked air filters! lol.
Yes nice for a quick plug change arent they
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Old 19th December 2004, 04:06 PM   #10 (permalink)
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They are cold plugs (#9 IIRC)

The misfire was odd as it was only at a certain revs when it wasnt under much load...

It's fairly heavy state of tune (2.7, T88 34D, 1000cc injectors, lairy cams etc etc) so I expect it to run 'rich' anyway, just not that rich I guess!
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Old 19th December 2004, 05:17 PM   #11 (permalink)
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Chris, I've got a box full of black iridium's out of the Garage Bomber. 9 is seriously cold for general UK use and probably only needed for warmer days and when giving your car some serious use! I find even 7's blacken up on normal (short) runs, usually needs at least 20 miles to get things cleaned up. Of course the Nissan ignition system is not exactly the bees knees either. Good CDI with top spec, Ultra HV coils certainly helps. The soot "leeches" the power instead of giving you a nice fat, hot spark, a good CDI/coil set up helps compensate.

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