mastacox

SO, I have had my 4Runner parked for about a week, and I get in it today to go take it for a drive, and I had the strangest problem.

I start the engine, which takes a little bit longer than usual to start (maybe fuel leaked from lines...) but once it does start it begins idling very roughly, almost as if one or two cylinders aren't firing

This surprises me as it has been working perfectly up to now, so I give it a little gas and the idle smooths out after a couple of pumps of the gas (and subsequsnt revvings of the engine.) I look out my window and there are dark gray to black wisps of smoke going by my window, apparently emanating from my exhaust. I give it a couple more guns and sure enough black smoke is dumping out of my exhaust pipe every time I gun it (from about 2000 - 3500 rpms).

I let it idle for a bit and the smoke dies down, but every time I gun it the smoke returns in about the same rpm range. So I turn off the car fearing bloody destruction has occured in my engine, and I had to be somewhere so I left it. I come back about 4 hours later, start up the truck, it starts fine and seems to idle nicely, but I gun it and some smoke still comes out.

So I take the car out for a drive, put some new gas in it and take it out on the road and hold it in second up to about 5500 rpms, and then engine brake back to about 2000. After about 6 miles and two of these burn ins, the smoke has gone completely. Everything seems to be fine...


So my question is: what is black smoke indicative of? Is it incomplete combustion (I know white/light grey is oil, but this is black)? The spark plugs are about 2 years/20,000 miles old, could this be a factor? I'm thinking a misfire in one or a couple of the cylinders caused some sort of a build up that had to burn off? Anyway, input would be greatly appreciated. Oh yeah, the gas in the car was maybe about 2-3 weeks old, possible break down (hmm, probably not...)?

I'll probably think about cleaning my O2 sensors, maybe look at one or two spark plugs to look for possible damage/wear. Thanks for your help

superjoe83

could be the cold start injector sticking open, (if 3.0 has it), if it doesn't do it any more, i wouldn't worry about it, but if it does you could damage your cat, grey/black smoke tends to be excess fuel

Slowrunner

I wouldn,t worry about it either. Mine doesn,t like to be left sitting for longer than a couple of days. It starts rough,although no black smoke (carbon),like its running on 4-5 cylinders for a couple of minutes until its warm.Then no problems. I wouldn,t gun-it until its been running for a few minutes. Give the oil a chance to do its job.I will only rev mine to 2000 rpm maybe 2500 if it needs it. 1990 V6 3.0L Auto. 4Runner

mikedog

Cleaning the O2 sensor will probably have little effect on start-up because they only operate in closed-loop. Closed-loop is when the engine is fully warmed up and under O2 feedback control.

Like the others have mentioned, check to see if the cold start injector system is working properly.

Another thing you might want to check is the coolant temperature switch. We had a similar problem on my uncle's vehicle (different make and model though) running rough when cold and it turn out to be CTS switch. The connector melted on the sensor and the wire inside was shorting out.

gwhayduke

Sounds like leaky valve seals to me. Oil leaks down the valve stem and into the intake port or into the cylinder itself. When you start the vehicle, you have to burn off this layer of oil.

It's not necessarily bad, lots of valve seals leak as they get older (Ford small blocks come to mind), but it ain't good either. You might try doing an Auto RX treatment. If it takes care of the problem, then you just had dirty seals. If it doesn't, you're gonna wind up doing a valve job sometime in the future. But you can drive a vehicle with bad seals for a looooong time as long as you don't mind it smoking on startup.

mastacox

But burning oil is a white to gray smoke, this is black.

gwhayduke

White smoke is blown headgasket (steam or antifreeze vapor).

Gray to black is unburned hydrocarbons. Oil or overly rich mixture. Sometimes when you do a Seafoam or Marvel Mystery Oil treatment you'll get black smoke. Alot of guys blame it on burning carbon out of the cylinder. I'm not so sure it's anything more than just unburned hydrocarbons.

TACOMANATOR

Black smoke indicates a rich condition. Blue smoke indicates oil.