What causes black soot on a gas engine car?

It's a rich mixture. Most cars' ECUs are tuned to go very rich at WOT, since leaning out at full throttle or high RPM means very hot EGTs - melted pistons, burnt valves, etc.

General rules are:

Black smoke/soot - rich mixture
Blue smoke - oil
White smoke - coolant (or water vapor)
Green smoke - awesome

 

Red Smoke?
http://www.youtube.com/watch?v=W7jddkmncEE&feature=fvwrel

 

I knew it was going to be those colored smoke tires!

 

What about if I'm encountering a purple haze? :hmm:

 

Why don't you quote me if you want to disagree?

Maybe I should clarify: EVERY car puffs some black smoke out initially when you floor it. I've never seen any car, ever, that doesn't.

Now, I did not mean to imply that if you floor a car, it'll just blow black fuel smoke until you let off of it, but when you initially floor it, there will be a puff of black smoke. It's unavoidable. When you floor a car and it goes to full rich, the initial dump of fuel doesn't all get burned, and you get a puff of smoke.

Some do it more than others, but all do it some. Ride behind someone's car and have them floor it while you watch the tail pipe, you'll see it.

 

Pretty much what I was taught long ago.

But you forgot one white smoke source, someone dumped a bunch of ATF into your gas tank.

 

Stop taking LSD.

 

This. I've seen puffs of black smoke behind modded cars and stock cars. I've seen it correlated to acceleration enrichments, which are typically much richer than normal running conditions. My MS3 hits ~9.3:1 AFRs there, resulting in a nice little puff of black smoke for a moment.

 

Jeez, my Supra (stock ECU) will dip down closer to 8:1 at WOT. It's kind of a disaster if you're in the wrong part of the power band and the turbo lags. You can really leave a nice cloud. 8.4:1 compression, off boost, and 8:1 AFR.

 

The car will actually run with ATF in the tank? Nice. I did not know that.

 

A quart to 15 gallons I don't think would have much of an effect other than maybe some smoke. It was used that way in the Wankel engines at times as seal lube so that the oil injector could be removed. ATF smokes like a mother though if the concentration is high enough.. On the mid 80's fuel injected RX-7 with the leaking fuel injectors, a couple of cap fulls was a quick way to start the engine and break carbon out of apex seals.

Biggest issue I can see is ATF loves to devarnish stuff so it might stall the car if the fuel filter gets plugged up with the trash that was in the tank.

 

ATF is basically Seafoam (in practice- I know they're not actually the same). Maybe better. I've never had occasion to use the latter, but ATF does a great job of desludging engines without resorting to solvents. I've heard of it being IV'd into the intake as an induction cleaner, too, but that's a bit more doubtful...

 

Personally, I would NOT want to burn ATF, gear lubricating additives in ATF are cancer-tastic.

 

It was fantastic for cleaning up wankel motors. If you had a stuck seal you would let the engine ingest some and leave it sit for a few hours then restart. It would below smoke but once it started the ATF helped keep compression until you could hold the engine revs up a bit at which point if you were lucky the seals would unjam.

 

It's a safe bet that any petrochemical in that ATF red color is bad for you.

 

Speaking of AFRs, found this old video:

https://www.youtube.com/watch?v=v1I9ZjdbdcQ

Gives you a decent idea of what its doing.

 

This is true most of the time it leaves soot on your tailpipe before your service light comes on or before you notice a performance issue . Kind of a precursor to the unknown .

 

Marine shops like to use ATF to winterize engines. Fill the fuel tank(s)and add stabilizer, connect a hose to the outdrive (or water intake), fire the engine up, bring up to operating temp, shut down, change oil and filter, fire it back up, check for leaks, rev engine to about 2,500 RPM and pour ATF into the intake (enjoy the white fog you create!) while keeping the revs up until about half a quart is consumed and then let the engine idle down and die. In the spring you change the plugs, check/replace the distributor cap/wires, change the fuel/water separator(s), clean the spark arrestor(s), connect the water to the inlet, fire the engine(s) up and let the white smoke belch forth until it clears up, then complete the tune up.

There's lots more to winterizing but the ATF part was always a blast. Former marine mechanic and service manager here...

Regarding the black smoke and fuel injection: Getting fuel injection to play nice with huge overlap (reversion) leads to all kinds of fun, hence the smoke on fast rigs upon sudden, hard acceleration. I've seen some pretty cool sights like how low RPM reversion on a four way Weber 48IDA system with a huge cam would spit A/F mix up out of the throats and suck it right back down on sudden acceleration without missing a beat. Getting fuel injection to deal with that takes some skill.

The best advice is to just stay in the throttle until it clears up!