Gas and Oil Home Heating Furnaces - Gas odor in flue exhaust

We are noticing an odor (outdoors only) that seems to be coming from the flue exhaust area. The flue box has black soot around the opening. We have a Trane gas pack. What could be causing the odor and soot?
P.S. The three burners were replaced last year.

Sounds like you don't have a clean flame at the burner. Soot would indicate a fuel rich mixture. You can check it if you have the manual for your furnace. It involves adjusting a damper to get the right flame color. If you need to, call a Heating Contractor.

Did this just start???? You said new burners last year WHY?
It could be anything from spiders got down in the burners. The W/C pressure on the gas is not what it should be. You didnt say LP or Nat.
Also the air intakes on the venturi not set right for a good burn.

;) ED

most newer (12 or so less yrs old) trane gas packs usually have shotgun burners....how old is it? regardless of age, what you have is inefficient combustion, definately get someone out there, but be sure they have a combustion analyzer, make that a prerequisite of who you get out there. this will eliminate guessing and unnecessary repair, as well as weeding out the "non pros". possibly dirty burners, incorrect gas pressure, etc

did not catch the new burners, is this on LP gas?

It is a Trane gas pack (about 10 years old) that runs on propane. The burners were replaced a year ago. Also, about a month ago we replaced the roll out switch. Now we are getting an error message that says the roll out switch is not working. Obviously there is another problem causing this switch to cut off.
We have called a contractor and are waiting for them to call us back. We will ask about the combustion analyzer.
Thanks for the info.

On the LP gas make sure they check the W/C on the gas pressure and that the regulator is ok and working right. You sure you have the right orifice in there for the LP.;) ED

i know they are only one year old, but clean the burners, it cannot hurt. being outside like that in a gaspack, and using lp, a lot of corrosion takes place. the burners could be dirty enough to prevent complete combustion (80%) yet clean enough to keep all burners on. many times those units go out because the burners are too dirty to run all the way across and get that last one, which has the flame sensor.