My entire exhaust setup is new, I have SLP 1-3/4 headers, SLP Y pipe, Magnaflow cat with the air tube plugged, 3" over the axle with a single exit flowmaster super 40 with a turndown just after the axle. After getting on it I often smell sulfur, or "rotten eggs" coming in my window. Is my new cat defective? I smell it a bit driving normally, but not as bad.

 

That smell is excess fuel reaching the convertor and being oxidized by the convertor. It will eventually melt the catalyst if its severe enough.

 

If you are not going to use your AIR system change the cat to a 2 way cat (w/out AIR). Rotten egg smell should go away.

 

cheppibearIf you are not going to use your AIR system change the cat to a 2 way cat (w/out AIR). Rotten egg smell should go away.


Rob WadeThat smell is excess fuel reaching the convertor and being oxidized by the convertor. It will eventually melt the catalyst if its severe enough.



Rob is correct. Fix the issue with your fuel system or you will be getting a new cat converter real soon!

 

Often when adding headers the computer overcompensates and dumps more fuel in the exhaust, a tune would fix your issue imo

 

I'm constantly tweaking the prom. I'm running open loop decel, so it jumps into open loop upon lifting the pedal. With the installation of a wideband I discovered anytime it enters open loop decel mode (regardless of speed) my AFR was dropping into the 10s. Got that fixed and I haven't smelled it since.

 

Makes sense and I do not disagree, however why get a 3 way cat with AIR and not use the AIR line to the cat (makes no sense). You are basically telling the convertor to work less efficiently.

Changing to a 2 way cat (w/out the AIR line) worked for me (no more smell). Of course I had no computer controls and at the time my setup was VERY lean for my motor with a stock 3310 carb and full MSD 6A ignition.

Of course this was later changed and cat removed for the racing days.

 

2 or 3 way w/o air, you shouldnt smell rotten eggs all the time. In PE, sometimes there will be that smell, especially with some cars as the air fuel ratio is richer, but not immediatly rich enough to stop most of the combustion in the cat.

Darkshot, what AFR are you running in PE? Id shoot for around 12:1 or so or less. This will help starve the O2 out of the exhaust, and keep the catalyst cool enough not to melt down.

 

Not unusual to smell this when under severe load. I drive to work on a road with a couple long steep hills and I smell this from new cars all the time. The excess fuel or whatever should burn out in short order though and the smell should go away. I read somewhere that OE converters used to have a nickel compound in them to reduce this smell, probably don't do this these days?