99 gt 3800 rotten egg smell

**mikedinthecity** · 10-02-2009

had a 99 gt plastic intake 3800 vin k come over and seems like it is running lean, rotten egg smell after driving lil on the harder side just putting it under load so i can feel the miss.....i changed the icm witrh a used one and it ran smooth. i havent seen a code yet. after restarting it and driving it searching a noise when you turn, i come back let it idle and go to rev it and theres the identical miss. it seemed to clear up and all but smelled like rotten egg after reving. all the iat coolant temp throttle posittion, both o2s, maf, map, all are reading correct. i took the module in to test and it failed, do you think simply the one i put on is faulty also, coincedence? or something make them both fail . any info would be helpful. new plugs, new wires, new coils. new polastic intake..this my first time attempt at this one.

**blueguy** · 10-02-2009

I thought rotten egg smell was bad head gaskets?

**mikedinthecity** · 10-02-2009

never heard that. research says cat but its running lean and thats why the cat smells, i was thinking vacuum or intake leak?

**Jakegday** · 10-03-2009

i dont think running lean would cause the cat to smell, running rich might though

from my experience that smell means your cat is bad, or is going bad. try disconnecting your downpipe from the rear manifold and see if this improves your situation.

**OH4CompG** · 10-03-2009

Originally Posted by Jakegday

i dont think running lean would cause the cat to smell, running rich might though

from my experience that smell means your cat is bad, or is going bad. try disconnecting your downpipe from the rear manifold and see if this improves your situation.

Yup, rotten egg is burning cat. Usually caused by dumping unburnt fuel into the cat and it overheating. However if you're running a lean condition I suppose that could heat the cat pretty good too.