When I let my car sit and idle for just a few minutes, what makes the huge black soot spots on the driveway ... behind the tailpipes? It's moisture mixed with soot. Could this be engine problems or does normal overnight condensation just simply flow out the exhaust and carry the soot out with it? It leaves a HUGE black spot about 12" wide or more.

 

might just be running really rich at idle especially with the cam. moisture is normal especially right after startup but the soot may be from too much fuel. Did you get a street tune or just a WOT dyno tune for the cam?

 

Mine is doing that but my only mods are lid, cutout, and Jantzer tb. My gas mileage has gone to **** after the tb so I'm guessing its running really rich and dumping fuel.

 

You possibly have lazy o2 sensors. Theyll cause you to run rich, kill your gas milage and make you smoke black at WOT. I assume it could also affect idle.

 

NLP tuned the car, recently. A/F was right on the money ... went back a couple weeks later (in January of this year) and the A/F was still the good. I dyno'd with my cutout open.

With the Borla restrictive plate now installed in my exhaust, it was pushing all exhaust though the Borla muffler ... that should have made it run more lean ...

 

Mine Z28 does the same thing at idle and blows black smoke at WOT only in the warmer months. In the winter it does not blow black smoke at WOT.

My WB shows the AFR to be 14.7:1 at idle and 12.7-12.9:1 at WOT. All I can figure is that the engine is experiencing incomplete combustion. Maybe a timing issue?



John

 

FWIW.. I had the same problem until changed both of my o2s. I deleted the rears.

 

The soot can also be caused by the cold start inrichment, inwarmer weather especially with a little bit larger cam it can cause noticable soot in the exhaust. Shouldn't be anything to worry about though.

Brad

 

My rear O2 sensors were turned off, as well. Mine also gives off a black smoke signature at WOT ... as soon as I hit about 5500 rpm's. Maybe I'll try changing out the 02 sensors and see if that fixes the prob. If I hit WOT several times really hard, there's like a mist of oil on the right side of my car ... some sort of blowback or something. Wouold bad O2's cause that, as well? There's no oil on the engine, anywhere. It's like it's being blown out of the crankcase in the form of smoke ... weird stuff.

 

Are you running the stock fuel injectors?

 

No, upgraded when TSP had the entire rail and injector assy with the 28.8 Bosch injectors on sale for $60.00 ... just couldn't pass that deal up. Duty cycle is below 80% at WOT.

 

spraying oil doesn't sound good...may be a compression problem

 

You're telling me ... MAN!!! About the same time all this started happening, I developed the 'sewing machine sydrome' in the valvetrain. It runs damn good, though.

 

Catch can may help, others on here have said that it helps with the soot/smoke. I've only had mine for 500 miles, but I've caught about 3 ounces of smelly oil that would have ended up in my intake manny.