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Dear Blindboy,

Hope you're well. Carbon inside the tail pipe suggests an over-rich fuel/air mixture. That can coat the catalytic converter ("cat") with carbon, and "kill" the "cat". Replacing a failed "cat" is not a cheap date.

That said, yellow-top injectors are the correct ones for a non-turbo-charged engine. However, if an injector malfunctions - and sprays too much fuel - the excess fuel: (a) is expelled with the exhaust, and burns outside of the cylinder; (b) contaminates the oil supply.

Pull the oil dipstick and sniff the oil at the dipstick's cross-hatched bottom section. It you smell gasoline there, that suggests an injector has failed. Excess fuel has fouled the oil supply. Replace the injectors and change the gasoline-contaminated oil and filter.

Hope this helps.

Yours faithfully,

Spook