only 1 black sooty spark plug

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Andy - 28 Apr 2006 15:02 GMT

I removed all 4 spark plugs on the wife's Fiat Punto 1242cc 8valve 1999 60s
Mk1 single point injection.

All 3 had right colour. 1 plug (on number 3 cylinder I think) was black and
sooty buy dry, as if too rich mixture. - anyone know what this denotes and
what to look for and can it be an extensive and expensive problem with the
engine?

The engine is idling a bit lumpy (like its only running on 3 cylinders
instead of 4) but when going at speeds of 40,50,60mph is as smooth as
anything and not misfiring or any thing.

Any ideas please?

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ato_zee@hotmail.com - 28 Apr 2006 19:51 GMT

> All 3 had right colour. 1 plug (on number 3 cylinder I think) was black and
> sooty buy dry, as if too rich mixture. - anyone know what this denotes and
> what to look for and can it be an extensive and expensive problem with the
> engine?

Might be worth doing a compression check, this should show up
a head gasket or ring failure. If all cylinders are same within a few
percent, move onto an emission check to see if that throws
anything up. There are several sensors, anyone of which can
cause overfuelling, plus the HT generation and plug leads.
Or just clean/replace the plugs and have another look in a months
time. A lumpy idle is not uncommon and the cause often
elusive unless you find a specialist, with expensive diagnostic
equipment, and more importantly the know how to use it correctly.

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