Hey Scotty & everyone,
I posted about this a couple months ago, had some great tips from everyone but sadly nothing resulted in fixing the problem, so I'm trying again.
To re-cap, 2005 Pontiac Bonneville GXP 160,000 miles. When cold starting after about 20 seconds there is a very strong Sulfur stench from the tail pipes. Once the engine reaches operating temperature the smell is gone. With the age and mileage of the car I'd be best to ignore it but my curiosity has peaked and I need to figure out this problem regardless of money. I'm also using this as an opportunity to learn how to DIY so I'd like to continue the journey.
Here's what I've tried:
Replace catalytic converter - there was a low efficiency code, so this was the first thing tried.
Replace spark plugs - plugs were quite old, 1 & 4 had oil on the plugs, might replace valve cover gasket but I don't see how this could be related.
Have battery inspected - Battery is 2 years old, no problems reported.
Fuel system/injector cleaner - Ran this through a couple of tanks of gas, no change.
What could I be missing? Should I replace the fuel pump? There is an evap code P0455 Evaporative Emission Control System Leak Detected Gross Leak. However, that code has existed for years.
Well, there's only two things that can make saw for smell. One is battery and the other is sulfur in your gasoline burning the catalytic converter. It's pretty easy to tell where it's coming from, cuz if it's the battery you would open the hood and you'd smell it by the battery. If it's catalytic converter, you would only smell it coming out of the tailpipe in the back. Now if you change the catalytic converting you're still getting smell out of the back. You're buying bad gasoline and that's sulfur in it. I would buy my gas somewhere else then
Hey Scotty, love your channel and all the advice you give. I should have mentioned, the battery is under the rear seats (result of cramming a V8 in a V6 engine bay). I removed the battery vent hose, kept my doors closed, the smell wasn't immediate so I ruled out the battery. I bought a battery tester that should be here any day now so I'll double check.
I had a friend tell me the same thing about the gas, and I was actually going to a newly opened Shell station for the last 6 months so it made sense. I started refueling elsewhere but the smell is still there. However, I've only gone through only 2 tanks since switching. If it is the gas, could it have damaged the newly installed cat? I'm in Alberta and our oil is very sour so it being the fuel quality makes sense. But I've used Shell for the life of the car, I'm not sure why all of a sudden their refining process would be worse.
Thanks again for the tips. I'll keep you posted!