For the last month I thought one of my neighbors had a sewage leak, turns out it was my car. I have a 2005 Pontiac Bonneville GXP with 160,000 miles. During cold starts there's a distinct rotten eggs smell coming from the car for about the first 20-30 seconds, restarting the car warm doesn't cause the smell to come back. I read that it's a sign the catalytic converter is plugged. I hooked up a scan tool got P0420: Low Catalyst System Efficiency Bank 1. Took it to a garage and after they did their own tests concluded it was the cat and replaced it. However, the very next morning the stench is back as strong as ever. What else could be causing this? Did I waste a bunch of money getting the cat replaced? And most importantly, did the garage do the right thing or did they just make an assumption and charge me a bunch of money for an unneeded replacement?
check your battery
You may be on to something here. I didn't think it was the battery because it's inside the car but the vent hoses run underneath and exit a few feet from the back of my car. Will have to test this end of day. Thanks!
Have you been driving through New Jersey? :chuckle:
Hard to say if the converter really had to be replaced without knowing what tests were performed and more data, such as whether there was excess back pressure.
Have you tried different gas stations? You might be getting fuel with sulfur in it. Is there roadkill stuck under the car?
https://www.yourmechanic.com/article/3-reasons-your-car-smells-like-rotten-eggs
https://www.way.com/blog/why-does-my-car-smell-like-rotten-eggs-how-to-fix
https://techwayautomotive.com/my-engine-is-sputtering-and-i-smell-rotten-eggs/
Thanks for the responses Joe & Chuck! I've been a long time fan of Scotty's channel but had no idea there was a large forum of people to help, really appreciate the feedback on this.
I don't believe it's the battery because the battery on these cars are inside the cabin under the back seat and the stench is coming from the exhaust. One thing I did notice cold starting yesterday was the exhaust note was rough for about a half a minute, almost like sputtering. The car has a V8 so it has a fairly loud steady rumble but this sounded more strained.
Definitely haven't been driving through New Jersey, I'm in the frozen wasteland of northern Canada. I park my car in a garage so if it was roadkill the stench would be apparent every time I went in the garage.
The gas station was suggested to me by another amateur mechanic friend, there's a new station that opened by my work I've been going to (Shell). I've always used Shell gasoline for the 95+% of my fuel ups, but I've only been using this gas station for about 6 months. I think I'll give this a try and see what happens.
Since the cat was replaced the efficiency bank code hasn't returned. I have a P0455 Evaporative Emission Control System Leak Detected Gross Leak. However, I've had that code for years and it's extremely common in these Pontiacs, usually replacing the gas cap fixes it but it didn't in my case. Also, I may be mistaken but this warning code is prior to the fuel being consumed correct? Whereas the sulfur smell is a byproduct of the engine consuming the fuel?
I can deal with the smell, especially since it goes away, I just don't want to end up with a blown engine is 6 months because this was a sign of something more serious. If you think the used car market is bad in the U.S you should see it in Canada (everything in Canada is 30-50% more expensive than U.S). I'm trying to ensure the old girl lasts another year or two until things settle a bit in the market.
I spoke with the garage and they'd like to take another stab at it. They said they couldn't really comment on the justification for the cat replace. The shop has stellar ratings specifically for exhaust repairs so I'm not overly concerned they were trying to rip me off, they just did what the code said to do. However, I don't want to spend another $1,000+ trying to fix a problem that may not be a serious problem.
I removed the exhaust hose from my battery and started the car, no smell inside until the AC starts sucking in fumes from the rear. I ran the car near empty and tried refueling at another gas station of a different brand. It's been 3 days since I've done that and sadly the sulfur stink is still just as strong as ever. An associate suggested something could be in the muffler but at this point I think I may just have to live with it.