Burnt-match odor mystery

[Andrew M. Franklin]

Whenever I tow my '62 Flying Cloud with my '89 Suburban 1500 5.7 TH700-R4 I detect a mild to moderate odor that smells like burnt-matches phosphorus/sulfur like. It begins after between 10 and 30 minutes of driving and goes away within 5 minutes. Only happens on new trip after trailer has been sitting for a while. We drive the Suburban daily and never notice the smell when not towing the Airstream. During a long adventure with overnite stays and take-offs, it doesn't happen either. Any ideas?? Thanks. Sincerely, Andy

[Silvertwinkie]

Do a search on yahoo and type in rotten egg exhaust smell. I came up with this:

Complaint of sulfur smell from exhaust
Background
Customers may complain of a sulfur or ‘‘rotten egg” exhaust odor occurring during heavy acceleration, at idle following sharp deceleration from
cruising speeds, or when exiting the car after switching the engine off.

Causes:
Most of this odor is due to a tendency of all 3-way catalytic converters (TWC) - not just those in Saab cars - to store sulfur during steady-
state conditions. The converter then releases the sulfur as hydrogen sulfide during fuel-rich engine running conditions such as idle after
deceleration from cruising speeds or heavy acceleration.
Fuel is another factor that can contribute to the ‘’rotten egg” odor. The amount of sulfur content can vary between fuel brands, fuel grades, or
from one geographic area to another.
Action:
Please advise owners that the sulfur smell will usually lessen after the car is used for about 10,000 miles. If the customer’s car haas more
than 10,000 miles or the customer wants to take more immediate action, the following recommendations may assist them in reducing the odor.
1 Switch to a different brand of fuel. Sulfur content may vary between brand names. Advise the customer that it may take several tanks of a
different brand before the odor decreases.
2 Switch to a higher octane fuel. Premium grade fuel usually has a lower sulfur content than regular grades of unleaded fuel. Again, it may
take several tanks of a higher octane grade before the odor decreases.
NOTE
Replacing the TWC will not solve the odor complaint and is not recommended.

[jcanavera]

Originally Posted by Andrew M. Franklin

Whenever I tow my '62 Flying Cloud with my '89 Suburban 1500 5.7 TH700-R4 I detect a mild to moderate odor that smells like burnt-matches phosphorus/sulfur like. It begins after between 10 and 30 minutes of driving and goes away within 5 minutes. Only happens on new trip after trailer has been sitting for a while. We drive the Suburban daily and never notice the smell when not towing the Airstream. During a long adventure with overnite stays and take-offs, it doesn't happen either. Any ideas?? Thanks. Sincerely, Andy

We have experienced that also. An occasional whiff (4 different tow vehicles). Sometimes its coming from the vehicle in front of us. I do know that my exhaust is pretty fragrant until the van warms up.

Once though on my '91 Astro van and my SOB I had a similar situation only it seem to be very constant and had (we thought) a propane overtone to the smell. Once we unhitched we didn't smell it. I checked out the propane system on the trailer (I had a inbuilt leak detector) but found no problems. We took the van to the local Chevy dealer down in Branson who couldn't find a thing wrong. Drove home towing and the smell came back. Ended up taking it to my trusty mechanic who found a vacuum hose unplugged. He got it secured and we never had the smell again.

I always was curious how that smell got into the tow vehicle. If I remember right I only smelled it when the car windows were closed and the fan was pulling in fresh air. Opening the window dispelled most of the smell. I had a good exhaust system on the van and I don't drive with any of the back door windows open (I know that can suck in exhaust fumes). Made me always leery about what was getting into the car when I drove with closed windows.

[TomW]

Originally Posted by Andrew M. Franklin

Whenever I tow ... I detect a mild to moderate odor that smells like burnt-matches phosphorus/sulfur like... Only happens on new trip after trailer has been sitting for a while...

Andy,

I do not have a specific answer to your situation, but a few observations made while operating my '84 Suburban may help you either solve your problem, or live with it more comfortably.

To point out the obvious, when towing your Airstream, your Burb's motor is working harder which means it is passing more heat through the exhaust system. This extra heat ends up burning off deposits in & on the exhaust system which accumulated during the course of daily driving without your truck being under any significant load. Gone, as you indicated, in five minutes, there is no significant fire hazard associated with the burn-off.

Now, why are you smelling anything since the exhaust system is outside, and you are inside? I don't know for sure, but I have a similar situation, and I think it has something to do with tailgate/aft window seals, and the aerodynamics of the truck. Effectively, the exhaust gas is being pushed into the interior through worn gaskets and/or tailgate misalignment at certain speeds.

I notice a warm-up smell in my truck even quicker when one of my front vent windows is open (in certain postions, the vent window can suck more air out of the interior than it lets in. The depressurized interior can now suck more fumes in from the tailgate).

The exhaust leak path is always there, but you probably only notice a smell when the exhaust is particularly fragrant; In your case, it is the burn-off. In my case, it is unburnt fuel expended since the choke is still full-on.

A possible troubleshooting technique is to duct-tape the output of an electric yard blower to a partially open window, turn it on, and spray liquid soap suds around the tailgate & look for bubbles.

Tom

[CanoeStream]

Sounds like catalytic convertor to me -- they're well known to do this for 5 minutes or so until they get hot. I would pay attention to TomW's advice. What is getting in your seals after the sulfur smell has gone away? I suspect you get dust inboard of the seals when you've traveled a dirt road for a ways.