it's 06 g35 coupe that is having these issues.
It's been a long time since it gave out horrible, stinky exhaust smell. The smell is so horrible that i can't stay idling for warm up in the morning. Everything is stock, used mobil 1 extended performance about 2000 miles ago, spark plugs were changed like 20000 miles ago, A/T, and the car has about 60000 miles. I checekd the oil level on the dip stick. It read between low and high. The oil was pretty dark.
I checked for leak but everything looked clean.
Another issue is that sometimes when i turn on the engine, i hear slight grinding noise under the hood or inside the engine.
What could be causing all this?

 

Sounds like your cat converters have gone South. That's the same smell you get when you take them out and put in "test pipes". As for the grinding, that's normal. It's the valve train tapping until the oil pressure gets up. Mine has done it off and on for years.

 

The car has only 60000 miles and the cats mess up? damn infiniti lol It's the cat not the sensor?

I forgot to mention this w the grinding noise. It only happens at start up, right after the engine turns over. It grinds for like .3 seconds. It's more like metal grinding then valve train tapping. THis didn't happen like a month ago.

 

Yes, a sensor can do that to the cats. If it sends too much fuel to the motor it can burn out the cats, but you usually get a Check Engine light. Any yes, the valve noise comes from the cam chains and the valve train until the oil pressure comes up.

 

would any other things can go wrong if i keep driving with bad cats?

 

Depends, if the cats melt inside, they can plug up almost completely and that just chokes your motor till it will not run. The only thing that bothers me, you say you have not check engine lights?

 

no lights on dash.
everything looks normal other than the exhaust smell

 

Almost sounds like your cats shattered.

You only hear the noise upfront right? A shattered cat shouldn't be an issue with OEM's though.

 

The noise only happens at start up sometimes. near engine

 

Not to thread jack but I also have this problem at start-up but the smell usually goes away after the engine's warmed up. My car recently passed the CA smog test also so I think the engine should be running fine.

Do you guys think that theres a possibility of a broken cat because of the awful smell but passes smog test?