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Discussion Starter #1
Tonight I did a quick plug change, and all was well except for plug number 4 which was distinctly black compared to the others. 1, 2 and 3 were all a nice tan colour, as they should be, but four was black.

Does this sound like a faulty injector? Anything else I should be checking for?

TIA
 

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Discussion Starter #3

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Discussion Starter #6
Matthew said:
Was the plug sooty black or oily black?
Sooty black. Not desperate, but it looks quite different to the others...
 

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Saab Mad
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Sooty black won't be rings, probably not valve either.

Are all the plugs the same heat range? If plug four is a colder plug, then it'll get sooty in a stock engine. Which plugs are you using?

Could be a faulty injector that's sticking open, or getting lazy. You could swap injector four with, say, injector one and see what happens to number one's plug over a long journey.

Anyone else got some ideas here?

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From the sounds of it, it actually just sounds like a bad plug to me. Too poor a spark to burn what fuel is there. See, now doesn't that sound better than a hole in your piston!
 

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Or a blown head gasket between the cylinders. Compression test it. Pat
 

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Shh! We're only supposed to suggest happy things!

More to the plug though, that fault could be coming anywhere from the plug to the lead to the cap .

1. compression test, if its even across all cylinders, then
2. do a flow test of the injectors or swap them
3. inspect ingition
4. change plugs, run for a few days, pull and inspect.
 
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