[VaerO]

Hello,

So today when I drove home for my break as I checked the mail box I stop and gazed at my beautiful car only to notice the tip of the exhaust pipe was black. I went and had a close look and discovered it was simply some black soot, "nothing to work about, every car has this" I thought to my self. Then I remembered reading a post on this form saying  running to high a octane could lead to the car not burning all the fuel and thus leaving soot behind! So I googled what causes black soot and all the answers say its because the engine is 'running rich' which pretty much means the engine is getting to much fuel to burn in one combustion cycle. Most said the lead cause is a bad o2 sensor, but since my car is only about 5 months old I suspect it wouldn't be this. Could my use of 98 octane fuel be doing this? I've never but anything but 98 in the tank because I was told it would keep the engine clean and I would more distance per a tank out of it. Maybe I should step it down to 95? I was thinking I might contact Hyundai and see what they have to say... Do you guys have any thoughts?

[Phil №❶]

Need to be a bit careful here.

Fuel injected petrol engines, generally have a black exhaust, yet are significantly cleaner in terms of emissions than cars from the 60's. The readings that you may have encountered could be referring to old carburetor engines. Although dirtier, when tuned correctly they output a grey colour exhaust, if black, then they were running too rich. A good guide is to look at similar cars and engine types. I think you'll find that black is common. Remember that you are observing the coldest part of the exhaust pipe. You will find that there is not any soot up near the engine if you were to open the pipe. When the engine is running, you should NOT see any black or blue smoke.

[VaerO]

Thought I was over reacting, but I just wanted to make sure    I've been behind the car while it was running and have never seen any coloured smoke coming from it. So if the car wasn't burning all the 98 fuel, would a coloured smoke would be present?

[Phil №❶]

Fuel injection is an extremely precise method of fuel delivery. Coupled with the car's computer which takes many inputs from throttle, engine temp, engine load, air temp & pressure etc, to calculate the correct quantity of fuel for each cylinder, then times the precise moment to inject it into the engine for burning. No smoke should emit from the exhaust.

[rustynutz]

The readings that you may have encountered could be referring to old carburetor engines. Although dirtier, when tuned correctly they output a grey colour exhaust, if black, then they were running too rich.

It's my understanding the "grey" was actually caused by the lead content in the fuel back in the old days...