Carbon on exhuast - possibly the oil?

[RamAir5]

I've been hopping around the GM forums (Acadia and Traverse) looking for a reason why my exhaust tips on our Traverse have an unusual amount of carbon build up on the inside of the chrome tips. There are many differnet reasons being entertained on the other forums. I would like for you experts ( I mean that literally) a chance to chime in on what might be happening.

These direct injection engines are new animals. I have never had carbon build up on my exhaust before. I have to wipe them out about every 3 days or so. Is this a fuel issue or a possible oil being burnt issue? Some say fuel, some say the oil is burning off and leaving the soot. Any thoughts? The engine runs great and fuel mileage is a very good 19+ around town 26+ highway.

Will a UOA provide me with this infromation?

 

[Eddie]

Same with my Mazda CX7 DISI and I'm not the least bit concerned. Runs strong and fuel mileage is ~ 20.5 mpg.

 

[Spykem4e]

RamAir, I have the 3.6l vvt NON-DI engine in my car and its the same thing. Black soot on the lower part of the tailpipe. It never bother me. And with 116k miles on the odo, I use about qt per 4.5k miles to 6k miles, not bad at all since the car runs 8hours per day almost non stop.

 

[mechtech2]

Some cars do, some don't.
It doesn't seem to be an indicator of anything, unless there is a change from one to the other with the same car.

But DI engines in the USA are strangely rich. You'd think they would be lean because of legislation. I'm not talking about the feedback O2 system, but when it is overridden for certain conditions. VW GTI DI turbos are way rich stock. Tuning helps power and economy.

 

[Craig in Canada]

I think they're rich BECAUSE of legislation. It's just my recollection, but I think it was NOx levels or something like that meant that DI cars were tuned rich in NA. This, in turn, can lead to all of the fuel dilution, valve deposit, and other problems we're seeing - but mostly in NA only (because of this legislation).

It's like it's another "Nikasil" all over again. Major issues, but only in NA.

 

[rationull]

I've noticed this on various cars, too. Every Mazda3 I've seen (both the 2.0 and the 2.3 and including my wife's) have sooty tailpipes and that engine isn't even direct injected. I'd always guessed it was due to running rich by design to cut down on NOx emissions.

 

[Craig in Canada]

Soot is not unique to DI by a long shot. Carbon (soot) is a product of gasoline combustion. It's all over the combustion chambers and the exhaust system, except where there's enough heat to burn it off.

I noticed less soot in the pipes and clean piston tops instead of carbon coating in my BMW since using LCD FP products.

Add to the mix that oxygenated fuels generally fool the ECU into altering the mixture, supposedly for "cleanliness" reasons.

 

[saberz]

What type of driving do you do? Short trips? My exhaust gets the sooty carbon on short trips when its not fully warmed up. On long rides (I also use MMO) my tailpipe gets super clean, not a trace of carbon on it.

 

[RamAir5]

Originally Posted By: Anies
What type of driving do you do? Short trips? My exhaust gets the sooty carbon on short trips when its not fully warmed up. On long rides (I also use MMO) my tailpipe gets super clean, not a trace of carbon on it.


A mix of around town and highway miles. This is the first vehicle we have owned that has had excessive carbon build up on the exhaust.

 

[440Magnum]

Particulates out the tailpipe seem to have a lot of variability. Back in the 90s, I noticed a lot of Nissans that seemed to produce more soot than most other gasoline-powered vehicles, but they seemed to return decent gas mileage anyway. I see lots of obviously modified boy-ricer Hondas running around town that emit enough soot to stain the whole rear fascia. Heck, my carbureted 1969 big-block doesn't do THAT!

On the other hand, I've noticed that Ford pickups (gas powered, obviously) for the last 10 years rarely have any visible carbon even on the *inside* of the exhaust pipes. I'm not quite sure how they do that either.

Most cars produce enough carbon to stain the inside of the pipes, but nothing outside. Some chrome tips do show black "dribbles" where condensation picks up carbon inside the tail pipe and then carries it out of the tip.

If its running well, no codes, and decent mileage, I wouldn't give it another thought.

 

[Eddie]

I think some of it has to do with the temperature of the exhaust as it leaves the car. I've noticed that if I'm running long distances on the expressways that the exhaust tip is much cleaner and tan colored than when I do a lot of short trips.

 

[Craig in Canada]

Originally Posted By: Anies
What type of driving do you do? Short trips? My exhaust gets the sooty carbon on short trips when its not fully warmed up. On long rides (I also use MMO) my tailpipe gets super clean, not a trace of carbon on it.


In the past this car was almost highway only. It had carbon then. After moving to the 'burbs, having kids, going on fewer road trips the trips are shorter. This didn't change the carbon that I observed.

Regardless of the trip length, once warmed up I tend to wind the gears out farther and drive it more than my wife. It gets its share of both "means of conveyance" driving and spirited driving.

 

[zoomzoom]

it looks like this after day at the track

 

[shpankey]

My 2.3 DISI Turbo MS3 did this sooooooo SOOO bad too. My tailpipes looked insane black all the time. And when I got on it, puff of black smoke everytime.

Now nothing, adding a High Pressure Fuel Pump internals and some Denso Iridium ITV22 step colder plugs with a much smaller gap (.28) seemed to have completely solved the issue for me %100. I didn't even do it for that reason, but for another reason, but that was a side effect.

DI engines love fuel and lots of it. I always thought I was getting TOO much fuel and therefore the black soot out the back of unburnt fuel. So maybe it was the plugs? Maybe the HPFP? I dunno. Just sharing.

 

[Smokescreen]

My suburban's tail pipe is very clean, and it only gets soot on the inside of the pipe when I add too much two stroke to the gas tank. Once I correct the mixture it cleans up again on its own.

 

[artificialist]

Every Gasoline Direct Injection engine I have ever seen gets more soot on the exhaust pipe than every Multi Port Injection gas engine I see.

It amazes me that on my 2003 Saturn ION, there is almost no soot on the exhaust pipe, despite the fact that the engine contains no special technology to reduce pollution.

 

[Jakegday]

not sure if its carbon or not but my tailpipes get some kind of residue on them since removing my cat, putting on ported manifolds, and opening up the rest of the exhaust system

 

[lexus114]

which car? ^^^