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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5928
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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my 2007 suzuki swift produces a smell of sulphur in the cabin

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my 2007 suzuki swift produces a smell of sulphur in the cabin when at speed under strong acceleration,eg open road overtaking, usually as soon as i stop pressing accelerator the smell is there. never happens any other time. mechanic tells me all is well with computer system,mechanic says they have never heard of this problem. only 25000 km on clock. i use 98 ron petrol which is the recommended octane . although i make many short trips where the engine barely warms up , even on long journeys this still happens. have owned car since almost new , it has always done this. any suggestions?

Submitted: 1 year ago.
Category: Car
Expert:  Dr. Hamman replied 1 year ago.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.



The smell of sulfur is coming from the exhaust system with the engine under load. It is the catalytic converter breaking down the engines emissions into simpler more biodegradable compounds, they don’t smell good. Normally this exhaust is diluted in the atmosphere and no one smells it. What I am thinking is that exhaust is getting inside your vehicle. Normally this will be an exhaust leak, or problems with the placement of the end of the tail pipe. The most upsetting thing about that isn't what you smell, it is what you cant smell, CO (carbon monoxide). CO is poison orderless, and is undetectable by normal human senses. CO causes headaches, and much worse. I would get the exhaust checked. If it has been modified, or repaired pay particular attention to the placement of the tip of the tail pipe. Small things like the length or placement of the tail pipe can be everything. There are positions for the end of the tail pipe that work with the aerodynamics of the car and take the exhaust gas away from the vehicle, and other positions the tail pipe can be in that trap the exhaust in areas that draw the exhaust into the car. So these are the things you need to check into so you can get to the bottom of what is going on with your smell inside your car. Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.


I do not get paid for my work unless you rate at 3 to 5 Smiley Faces or Stars, a bonus is always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further.


Customer: replied 1 year ago.

are you saying that the smell is actually normal (under those driving conditions) but is somehow getting inside the car? no changes have been made to the exhaust and i have read that some other owners experience this but by far the majority do not. the entire exhaust system has been checked by mechanics and they have found nothing wrong. i have blocked off the rear air vent thinking this may have been the problem as its behind the bumper but made no difference. is it possible that a faulty oxygen sensor might be the problem in that so much of the sulphur gas is being produced under those exact conditions that you can't help but smell it?

Expert:  Dr. Hamman replied 1 year ago.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.



The smell is normal in the exhaust, but you shouldn’t be getting any exhaust into your car. Fossil fuels naturally have sulfur in them, so it is in all gas. In older cars you never smelled it, because they didn’t have aggressive emissions systems. Catalytic converters break the sulfur compounds down, and when they do it cam smell real bad. Also different catalytic converters will break down sulfur more aggressively, newer or good functioning converters normally put out the most smell when the fuel has a high sulfur content.


Another thing is you can many times help the exhaust smell a lot by changing the brand of fuel you use. It will take about 80 miles of driving to clear out the exhaust system. Crude oil from different areas of the world, have some pretty varied chemistry, it is amazing how consistent refinery’s are able to make gas, all things considered.

Anyway the smell is normal, but can be linked to the type/brand of gas. For the smell to be getting into your car, exhaust gas has to be getting into your car, not good, mainly because of the CO in the exhaust, it is VERY dangerous, and it is orderless. I would have the exhaust checked, and consider extending the tail pipe a few inches, ask a muffler shop what is advisable here, if there isn’t an exhaust leak.
Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.


I do not get paid for my work unless you rate at 3 to 5 Smiley Faces or Stars, a bonus is always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further.


Customer: replied 1 year ago.

thanks, did find two small holes (1 " dia) under the lining behind bumper that might have let in some fumes under the right conditions, i have now blocked them off . my question is : can even the smallest holes let exhaust fumes into cabin, do you get a kind of suction effect at certain speeds that draws them in?

Expert:  Dr. Hamman replied 1 year ago.

What happens is turbulence and areas of suction form under and behind a car. These are pretty unpredictable, but generally under a car a suction will form. The differing pressures can draw and move fumes around in strange ways. That is the dynamic that would seem like it would just blow the fumes away from the vehicle, but these fumes find their way inside the car. Patching holes can help a lot, so you might have already fixed the problem.

Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5928
Experience: 30 years experience, Repairing, building, & designing, automobiles.
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