foul smell

[de_shadows]

after replacement on a broken valve,
we resurfaced the head and put in new gasket and everything back the way it was.

after the surgery it runs great but there was fouled smell from the exhaust after 5 minutes of idleing.
then took to autozone and came out something like (p303) = misfiring
sparkplug from cyclinder 3 was powder black!

What's causing the miss firing and fouled smell?

 

[oldman]

Do a compression test.

 

[jott5555]

check the ecu it often make sa stank smell but.. i think you mean the smell is in the engine bay on occasion it seems after i built a engine there is a strange smell with the coolant. it may be stagnent coolent in the system or something. my bet is that it will go away after 40 or 50 miles