AusXH

Attatched is a picture of two sparks plugs that I've pulled out of my engine. They are both NGK iridium spark plugs model no BPR6EIX and have been in the engine for about 20k kays. The plug on the left is out of cylinder 3 and the one on the right cylinder 4.

Appreciate any sensible input for spark plug 3's demise.

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PVTXR01

Rollin

WTF? thats some strange sh!t you have going on there....it looks like the plug was siezed in the head, which would explain why the thread is so badly damaged, and the deposits on it could come from a leaking injector, slightly blown head gasket, broken piston ring, faulty ignition lead..any number of things that would cause foreign matter to enter the compustion chamber and/or affect the burning or ignition of that fuel/air mix.

check the compression first, then the leads, then the injectors to see if there is anything wrong...

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AusXH

Yeah, the plug was basically welded to the head. Any part of the thread inside the combustion chamber is gone, eaten away. The deposits on it look worse than it really was as the oil mixed with the alloy and iron filings from getting the bloody thing out dirtied it abit.

It was missing every now and again at idle, which was what made me check the leads (swapped them with a new set to be sure) and try different injectors, wasn't until the other day that I thought to check the basically new plugs. Under throttle it was perfect, still made good power.

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PVTXR01

460Fairmont

The plug on the left looks like it was cross threaded when it was installed and whoever did it just did it up anyway, that would have chewed the thread in the head aswell.

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useless

Hi mate ..that looks terrible .The first impression i got was crossthreading tooo...but i did a search on spark plugs and it shows that that cylinder ran too hot for the plug ..it was not crossthreaded ..
lokk at this link under the title"melted"
http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm
http://www.beru.com/english/produkte...gnosehilfe.php
Try another heat range too....
insufficient tightening?
http://www.densoiridium.com/howtoreadusedplugs.php
http://www.machv.com/melsparplug.html

jonbays

I am not sure whether you mean 20,000km oe 20km but either way you have a problem with no.3 cylinder. How was it idling and running?

Did you check idle speed drop on disconnecting each cyl and compare them?

Have you done a compression check?

How is the water in the radiator? Cyl head Gasket OK?

Checked resistance on spark plug leads? Are they all within spec?

You need to check this out 20-20,000 km your plug should still look like no.4

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galapogos01

the deposits on it looked like oil to me.. but if the thread is stuffed perhaps the injector for that cylinder is half stuffed, making it run too lean/hot?

jonbays

galapogas is right.

I had a V8 with a broken ring on one piston that ran ok but was low comp and had an oily black plug much like your no. 3.

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AusXH

I put all the plugs in originally, and it was definately not cross threaded.

Sorry, I meant 20,000 kays. Only in the past two weeks has it begin to miss on the odd ocasion at idle, and then maybe 3 or 4 misses during a 80km run down the freeway. When it wasn't missing it was running perfectly, was making pretty good power infact. Timing has been set at around 5-10'BTDC.

The idle normally sits right on 800rpm. When missing it would jump between 600 and 700. I didn't record or write them down as such, but noted a difference as I disconnected each plug, certainly less than 600 for all the cylinders but number 3. As expected cylinder 3 didn't result in as much RPM drop compared to the other cylinders (as it was missing anyway) and was around 600. Hope that makes sense.

Not as yet, will do that later today.

This was my initial worry. I've blown two headgasgets in my other engine and drove it for around 10,000 kays with it the 2nd time. It was so bad that if I let it sit for long enough, enough water/coolant would enter the cylinder and cause hydraulic lock and wouldn't turn over unless I first took the offending cylinders plug out. Yet after all that the plugs were still perfect, infact they are the plugs I've put back in this engine for the time being and its running perfect right now.

This engine has moly chrome rings and an o-ringed block, so I would hope its almost impossible to blow a headgasget under normal operation like it has been used.

Yeah, I measured the resistance of both the old leads and the new ones I put on (about a week ago, a week after it started missing). Interestingly the new leads (Champion Red leads) had around double the resitance compared to the ones that have been on there for the 20,000 kays (Bosch Super Sports), but both sets were consistant.

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PVTXR01

AusXH

This is infact what I think the problem is. Problem being I swapped a new set of blue 24lb injectors in there for a day when I changed the leads (about a week ago), but when I put the originals back in the next day I mixed them up so I cant be sure which injector that is now.

I have a bmw paddock basher with worn or broken rings/valve stem seals in 3 cylinders. Yet as much as I drove it as was, at worst the plug would get covered/baked in oil, I've never had a plug break down like this one.

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PVTXR01