Premature wear of one spark plug electrode

2007 Nissan Versa DOHC
Replaced all 4 spark plugs about 10K miles ago, premium NGK iridium type.
Cylinder #2 spark plug center electrode (sparking tip) worn to nothing already (no visible tip of electrode), and bench tests no connectivity thru core (infinite resistance). All other three have some electrode left and bench test OK.

None of the plugs appeared fouled or “carbonated” or appearing of too lean condition either. Color condition of #2 seems like the others.

Besides defect of #2 spark plug, what would be possible causes of its premature wear?

Iridium is very hard so it is unlikely that it just “blew off”. It is also very brittle so it can be easily broken off mechanically, that is why you normally do not re-gap them, it is too easy to break the tip off. There could have been a crack in the tip from the factory or from someone attempting to re-gap the plug, but the tip didn’t completely break off until it was in the engine for awhile.

Today’s ignition systems are very high voltage and high energy. They are capable of jumping a very large gap. When the tip finally broke off, it was likely broken just below the ceramic and the plug was still able to provide a spark for the cylinder.

The reason you are reading infinity across the core is that your meter probe can’t reach the end of the core up inside the ceramic, but the core still exists and a spark can still be made.

Were these plugs the NGK Iridium or the new replacement type you just put in the NGK, or both?

1 Like

If the replacement plug does the same thing, I’d suspect a coil, wire, or ground problem.


I’m guessing that spark plug was defective right out of the package. Installing a replacement will probably sort it out. If problem returns, you may have a pinging (early detonation) problem. For it to be severe enough to damage a plug in 10K miles, the pinging would likely be quite audible to an experienced mechanic.


I bench-tested the coils (resistances), and all came out same–I assume all in working order, since three of the cylinders were running fine.

I was having misfire on cylinder 2, so I assume the gap on plug 2 was prob just too big to fire properly. How would a ground problem happen on one cylinder? I assume ground comes thru engine body and the metal screw-in threads of the plug?
There was some oil seepage into spark plug wells #2 and #3, but #3 plug was still OK, similar to #1 and #4, and there was no misfire on cyl 3 either.
I’ve ordered new plugs and will switch coils for #2 and #4 cylinders to see if anything funny eventually happens to cyl 4.
I also will install a new valve cover & gasket, and use permatex high-tack gasket sealer. Hopefully that will adress the oil seepage issue.

I’m not exactly sure what you mean in this question. The spark plugs I installed 10K miles ago were NGK DILKAR6A11. I take it they are kind of on the “premium side” of replacements.

I’ve ordered new plugs and will switch coils for #2 and #4 cylinders to see if anything funny eventually happens to cyl 4.

The coil needs a ground too. I expect it gets the ground via its electrical connector. Check that coil’s connector pins for corrosion, etc. Some designs, the coils may get their ground by the installation method, the fasteners that holds the coil in place may also provides the electrical ground.

I expect the ground is ok and the misfire is the result of the defective spark plug.

Double-check the spark plugs you are using are one of the ones recommended by the manufacturer for your make/model/year/engine.


The PCM monitors the coil performance, that includes power and grounding. The computer monitors the cylinders for detonation and controls the spark advance accordingly. Everything is done for you, your job: don’t drop the spark plugs.


Good info and idea. Just went to check continuity on ground (center pin) of each connector-- all good to engine block. The three pins on each coil all look bright and shiny too. Would you recommend cleaning those connectors/pins now that I’ve got things open? A spray or electronic parts cleaner? Would just a spray of brake parts cleaner help?

That sounds good to me. I’ll treat the new ones like eggs.

Just another thought. You sai you were ordering them. There are knock off fake parts that look identical to the real thing. If you order, I would only order from some place like rock auto to be sure getting genuine parts. Some years ago an old parts guy at the auto parts place, told me that it seemed like plugs from the big box auto suppliers were of a different quality. He had no evidence except 30 years of experience but I’ve kept it in the back of my mind. Another said the gold tipped plugs versus the silver are worthless and throw them away. I don’t always have a choice for small engine and haven’t had a problem myself, but it is quite possible you got a bad plug.


I’m curious as to where you bought the plugs from??

I am also assuming the engine started misfiring and or the CEL came on is why you removed all the plugs after 10K miles(?)…

M money would be on a dropped spark plug at some point between the manufacturing machine and your cylinder head…

1 Like

Yep, I suppose a dropped one might be an explanation. Can’t say where I ordered them (it’s been a couple years) but I remember they came in nice Japanese boxes.

Anyway to post a picture of the damaged spark plug??

There are counterfeit, high dollar spark plugs out there.

1 Like

My first thought too.
Lots of phonies on Ebay and Amazon.

1 Like

Nothing needs to be done imo. Based on your report, I don’t think your problem is related to the coils.

This is why I don’t buy anything from third party marketplaces that I cannot tell is legit. I don’t know how many tens of thousands of dollars in computer equipment I have seen ruined by cheap crappy replacement chargers and power supplies from China. Other stuff breaks but it doesn’t ruin the equipment it is attached to. The $10 chargers off eBay, Amazon, etc. should be illegal.

People tell me I can get car parts cheaper off the internet. I buy locally from a parts store even if it costs more. Warranty is also easier if needed. A mechanic was telling me about a customer that bought some no-name starter off the internet. It locked up on like the 2nd use and the force of the engine sheared it off, cracking the engine block beyond repair. A cheap starter totaled the car. I see the same thing with cheap AC to DC chargers and power supplies all the time. If you cheap out on computer parts, don’t cheap out on those!


Thanks for ideas, everyone.
What I’ve learned:

  1. Treat plugs gingerly. That means a lot of plugs sent by mail are suspect if not packed very well with sufficient boxing and padding. Packages get knocked around a lot by the mail people.
  2. Always bench-test plugs before installing. Don’t assume they’re good.
  3. Be very wary of NGK counterfeits (perhaps other brands too), which means avoid small discount sellers (like Amazon/Ebay) for such items.

Just picked up four new iridium ones yesterday from O’Reilly.
Tested them with multimeter before taking them out of the store-- all tested OK. Installed them, put back intake manifold, and car runs fine now. I’ll cross my fingers that they last more than 10K miles this time!

That was the same part number for your vehicle that I show, not sure of Denso or NGK was OEM or not but either brand is best for you make…

Just my opinion but I usually don’t buy any car parts at oreilly or az. I stick to cleaners, bulbs etc.