Sulfur smell when letting off the gas

[Matt Buffington]

Hi Gang! Just had true-dual exhaust added to my 1990 burb, with high-flow cats and flow master mufflers. Truck runs amazing. However, when I let off the gas, I get a sulfur smell in the truck if I have the back window down. I know, simple solution to this is to drive with the window up! But I’d rather figure out what’s happening. I’ve heard it ‘could’ be running rich, others say ‘could’ be lean! Still others say ‘could’ be breaking in....the latter I can;t really believe as I just finished 500 miles in the Allegheny mts this past weekend...seems like that that should have broken them in....so, any ideas of what to check? Timing is as 0 TDC, IAC set to 625. I reset everything after the mod so the computer could re-learn. Thanks!

 

[QBuff02]

There could be a couple of things going on. I'd be curious to bump the timing up on it, to say 8ish degrees btdc. If the timing is late, it can cause incomplete combustion and the cat is trying to pick up the slack. If its running rich it could also be causing the cats to do extra work. But you say I runs good, so.. If the computer is still learning it might not be optimized yet, but just based off of the info you provided, the timing is a good place to start in my book.

 

[QBuff02]

Oh, and I should add... nice last name..

 

[Matt Buffington]

Thanks for the advice. While it drives well, it does have the feeling of retarded timing....even though it’s set to 0. Over this long weekend, I’ll mess with timing and see what results. You’re a Buffington, too? So cool!

 

[QBuff02]

Thanks for the advice. While it drives well, it does have the feeling of retarded timing....even though it’s set to 0. Over this long weekend, I’ll mess with timing and see what results. You’re a Buffington, too? So cool!

Yes, I am! Lol Small world..

 

[Raider L]

@Matt Buffington,

That smell is the catalytic converter. That sulfur smell is sulfur dioxide coming out of the catalytic converter.. When will it go away? I don't know, maybe it will get less over time but the gas you are smelling is a converter byproduct. Some people say it smells like rotten eggs.

 

[Rusty Nail]

It can take up to forty key starts for relearn to complete. An EASY twenty run cycles.
If you went with traditional rear exit pipes, I believe you may find that a side exit will be more appropriate for your Sub.