My buddy noticed that when I got on it (WOT from a stop through 2nd) that my car had black smoke coming from the tailpipes at the higher revs. He said it was rather substantial, covering up part of the rear of the car and blowing off to the side in the wind. I do not have any soot build up on the rear bumper, but I do not got WOT that often either.

Obviously the car is running rich at WOT, but the only engine related mods are SLP Lid and SLP Loudmouth cat back exhaust. I am still running catalytic converters and the car has only 39,500 miles on it.

I guess I am wondering if this is normal, or if it could be the result of the mods and what I should do about it? Is it possible that the lid is not sealed to the MAF and there is un-metered air entering the system (I thought this would make it run lean though)?

Thanks for all the help guys.
Eddie

*EDIT*The car still runs very strong and barked the tires going into 2nd. I do not know if fuel mileage has changed much as I do not pay that close of attention.

 

Probably just cleaning out the cats.

 

You see it all the time on a dyno. The first pull is usually very smokey.

 

The mods you have shouldnt make you run rich not even at WOT nor do I believe you would blow smoke due to that. black smoke is usually due to burning oil but not sure even why your car would be burning oil already, probably just dirty cats like said before. But not totally sure.

 

I am not sure on the black smoke either. However, I can assure you that it is not burning oil (blue smoke by the way) as it has been 4,000 miles since my last oil change and the level is spot on.

Several of you have mentioned dirty cats. Why would they be dirty?

Is it correct that un-meterd air causes you to run lean and not rich?

 

Unmetered air can cause you to run both rich or lean. It depends on where it enters the stream. If it's before the cylinders, then yes it'll cause a lean condition because there's more air than fuel. However if it's after the cylinders (ie - in the exhaust), it could cause you to run rich. This is because the O2 sensors might pick up the extra oxygen content and tell the PCM it's not adding enough fuel. The PCM then compensates by increasing the fuel trims and the next thing you know, you're running rich.

If you are running rich, the two electronic contributors would be either the MAF or the front pair of O2 sensors. If they aren't functioning properly, it will affect your fueling. If they are functioning properly, then I'd say there's a leak somewhere that needs to be sealed up. Either way, you shouldn't be running an AFR richer than 11.7 as this is usually the richest they get from the factory. There's also a safety factor built into the PCM's fueling to protect the cats called Cat. Overtemp Protection (sometimes called COT on the tuning boards). This dumps in extra fuel to keep the cats from overheating during extended WOT runs. I still never saw AFR's much below 11.7, even when this kicked in. Find a friend with a wideband and see where you're at. That's the only way you'll know...

As for my comments about the cats...they can collect crap over time with just light throttle application. Get some exhaust flowing at a higher velocity through there every once in a while and it'll blow that crap out.

 

Well, I have no codes and low miles so I am going to assume (I know that can be dangerous) that the MAF and O2 sensors are working properly.

The car is lowered and the y-pipe or resonator will occasionally scrape on things eventhough I am very careful. Perhaps something could have come loose. Then again, it could very likely be dirty cats as you mentioned because I do not get on the car often.

I will check the exhaust for leaks and if I do not find any then everything is probably ok. I may also do a couple WOT runs and have my buddy follow me to see if the smoke goes away on the later runs, which would indicate that it is just dirty cats, correct?

Thanks guys.

 

You say you don't get on WOT much,could just be some carbon build-up that will get blown out the exhaust when you get on it hard.It doesn't sound like you have anything to worry about.I use Gumout Regane Complete Fuel System Cleaner & have used it for years.I used it on my '84 cause I had a pinging problem due to carbon build-up & it took care of it with the 1st bottle.Now I use it at every oil change.It works great at cleaning out the fuel injectors & combustion chambers,etc.Cleans the carbon out out & keeps it clean.WalMart carries it in my area.Amber colored liquid in a clear bottle.

 

YEah. I asked about that when I dyno'd my car. He said that the LS1's smoke a bit at high RPMs. I notice it in my rearview at high r's. If it get's REALLY thick, they I'd start to worry. Once you get it tuned, it dissapates a bit due to a leaner mixture.

 

I thought I should mention that I have recently noticed a faint sulphur or "rotten egg" smell immediately when getting out of the car after parking. I have noticed this on two occasions now.

I know this often means the cats are going bad, but I just can't believe that would happen at 40k miles! Any thoughts...

 

cats can go out at anytime rly.... just rarely...

just go LTs and screw the cats... no more worrying!

cory

 

Longtubes are not an option as the car is very low. Regardless, I don't have the money right now. I know an exhaust shop that would remove the cats and weld in a piece of pipe for cheap. Do you think I need to do that?

Wouldn't there be a code if the cats went bad?

 

I thought emissions had something like an 8year/80k mile warranty. Might want to check into that...

 

I hate taking my car to the dealerships around here as they are very bad, but I just might have to do that. I wonder if they will give me any grief for the catback exhaust...