Burnt plug electrodes, one bank only

[losh1971]

Anyone know why i would have slightly burnt electrodes on all three passenger side. Driver side all look good. No burns on ground strap, just electrode. Plugs are Bosch Platinum. I have used these for 15 years and no issues before. Seems odd all three on one bank are worn down and drivers side are like new almost.

Only thing is these Platinum plus are slightly different to what I have used in the past. Normally the Bosch Platinum don't have an electrode that sticks past the insulator, where as these ones from SCA do. I think the ones from SCA are the US version as the part number is US and not Aust.

 

[Lex]

What are the gaps?
One looks wider than the other?

 

[Immortality]

The wasted spark ignition system is a bit weird. Basically one side of the engine fires from the positive polarity of the coil, the other side the negative side of the coil. One side tends to wear out the electrode, other side the earth strap.

 

[Aussie Trev]

Maybe a slight air leak on that side between inlet manifold and the head making it burn lean?

 

[EYY]

I certainly wouldn't be spending money on special plugs. Standard copper core are the way to go unless you have accessibility issues like the alloytec where you need to remove too many components for routine servicing such as plugs.

 

[losh1971]

Used these plugs for yonks, since my old mech put me onto them and at $25 for six its not big money.

 

[losh1971]

The wasted spark ignition system is a bit weird. Basically one side of the engine fires from the positive polarity of the coil, the other side the negative side of the coil. One side tends to wear out the electrode, other side the earth strap.

That makes sense they were only a tad worn, just the other side were looked quite good. The plugs are probably 40k old so IMHO were due for replacement. They reckon 60k but I normally replacement at around 40k regardless. Good to know its normal and good to know i need to change them at 40k or sooner since the burning occurs.

 

[Lex]

Swap them from one side to the other at 20k?
Maybe they will wear more evenly?

 

[losh1971]

Maybe a slight air leak on that side between inlet manifold and the head making it burn lean?

I thought that but I replaced the LIM gaskets not that long ago and as the mech agreed it would miss if it had a leak. Mech had never noticed it before. I'd say it is partially because of the plug design having a little thin prob on top of the main prob. The new plugs are a better design, same as what I have used for years. Some reason SCA stock these odd ball Platinum plugs. I suspect with the new plugs I won't have the same issue.

What are the gaps? One looks wider than the other?

Yeah looks like gaps are diff, that's because one has burnt away.

Swap them from one side to the other at 20k?
Maybe they will wear more evenly?

Could do, but $4 a plug might as well just replace them at maybe 30k if the issue continues.

One good thing is I think the infrequent miss might be solved when I am idling at lights or in car parks. Google told me that worn plugs can have this affect.

 

[losh1971]

I certainly wouldn't be spending money on special plugs. Standard copper core are the way to go unless you have accessibility issues like the alloytec where you need to remove too many components for routine servicing such as plugs.

I think given that this design ignition system wears plugs; I would never go Iridium as they have a really thin exposed electrode like the tip of the ones I had installed and I'd say they would burn away. The new ones are better because the electrode is encased in the insulator with only the very end exposed, just enough to provide the spark.