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Car with newly rebuilt motor was tuned a couple of days ago with good results, with just a minor stumble when a misfiring ignitor module had to be replaced. Then it went back to the spannerman for some final mechanical work.

Today I've been told the fairly new fancy iridium IK22 plugs which were part of the Fab9 COPs kit have failed. They're the right ones for the relatively low boost the car is running. Apparently the coolant temp sensor had failed first, making the ECU think it was -5C, when it was actually +10C, supposedly causing enough overfuelling to flood the plugs and made them work overtime to produce a spark, which killed them.

In my day, many decades ago, when (cheap) plugs got too wet or sooty you just took them out and dried them or cleaned them.

Is it actually possible that four nearly new plugs capable of going 100,000kms have all died, or is something else going on here?

I've also been told (by a workshop I trust and who had no direct benefit from telling me so that fouled plugs would cause drama and it easier just to toss them. Apparently pulling them out and putting them on the bench under a (flame) torch can resurrect them though.

I replaced the plugs in question at the time but went for standard cheap $4 plugs (still Bosch/ ngk )

Yes they wear out quicker but if your not paying labor to change some plugs they are cheaper in the long run. If they foul or turn out to be the wrong temp they are much cheaper in the long run.

The mx5 runs the same plug as a Yaris I found out. So about a year later I threw the left over fouled ones in the missus car when her cheap plugs started to fail.

Car ran like a dog on the fouled plugs to start (I'd torched them in a BBQ flame for a while) but a bit of sedate driving till up to temp and then some full throttle / full rev pulls and the engine settled down and was perfect with 10 minutes. Plugs are still in the car to my knowledge after 2 years and have been faultless.


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Not another issue! Am starting to think you are seriously unlucky.

Are iridium plugs even necessary? Personally I'd stick with ngk, especially until all your sensors read properly and you are able to confirm not running rich after a run in period.

Try the ngk's and see how they run. You can always clean your iridiums and whack them in later.

Just my 2c

As I recall he can't run NGKs because they no longer make plugs with removable tops. Can't you change the connectors on your COPs, Dave?

Personally I would do as sailaholic suggests and give them a clean, it can't hurt especially considering the cost of those plugs. Once the spark plugs get up to their operating temperature they should self clean. Depending on the plugs, the self cleaning temp range is between 450 and 800°C.

AS for Speed's post, have the car tuned on 'used' plugs and once it is all sorted out swap the plugs out. I keep the plugs that were used to tune the car as spares.

Plug reading explanation:
http://www.gnttype.org/techarea/engine/plugs.html

manga_blue wrote:As I recall he can't run NGKs because they no longer make plugs with removable tops. Can't you change the connectors on your COPs, Dave?

True

IK22s were out of stock everywhere. IK24s seem to be doing the job for now. IK22s ordered online.

for reference, i've always just cleaned off plugs when they've been fouled.

Usually just a wipe off with a cloth is fine, but if not a blast of carby cleaner does it.

hks_kansei wrote:for reference, i've always just cleaned off plugs when they've been fouled.

Usually just a wipe off with a cloth is fine, but if not a blast of carby cleaner does it.

Thanks. I was told they'd failed, not fouled. Once upon a time I'd have done what you suggested, maybe adding a bit of work with a wire brush or some emery paper. But apparently these were beyond saving!

Beyond saving could also mean we're going to spend 70% of a new set in labour cleaning them and refitting them and they may not work or 100% of the costs and we know it's right.


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manga_blue wrote:As I recall he can't run NGKs because they no longer make plugs with removable tops. Can't you change the connectors on your COPs, Dave?

Maybe I can, but remember I only sell cars, and can't do clever stuff with spanners etc.
Will be pleased to hear if I can change the connectors so I no longer have to use these unobtanium things just because I can unscrew the tops. Mind you, with a colder set than needed working perfectly well and another set of the correct temp coming, I should be good for 200,000kms if the claims are right!?

sailaholic wrote:The mx5 runs the same plug as a Yaris I found out.

Nick, plugs are interchangeable through many makes and models. Besides the heat range, the only difference is thread pitch, length of the lower body, and size of nut (of which there are 2 sizes).

Most plugs for mainstream cars use the same thread pitch and the smaller of the two nut sizes, so the deciding factors are heat ranges and length of lower body (too long and ground electrode may hit the piston, too short and spark kernel is not in the optimal place).

Back on topic, I've been told that Iridium is junk, try the NGK Laser Platinum range if you want a longer lasting plug, or simply use top quality copper plugs but check them regularly.