jay123

hey everyone, I own a 1991 firebird with a 305 TBI and 5 speed manual trans. I just bought the car a few weeks ago and i notice that the exhaust smell is very strong, under the car the exhaust is straight piped and uses a glass packed muffler about 2 feet long under the passenger side floor where I believe the cat would have been located. I cant find any air leaking out of the exhaust piping while the car is running ,

however there is a small aluminum tube that is running along the exhaust that looks as if it would have hooked up to the CAT, while the car is running I can feel air coming out of this tube, could this be why the smell of exhaust is so bad? is it exhaust gas coming out of the tube? and lastly, what is it and what do I do with it if I have no CAT anymore?

Any help would e greatly appreciated.

88BlackFormula

I've been experiencing the same problem with my 88 Formula 305 TBI since deleting the cat.

My best guess for diagnosis is the following:

• if your car had a cat that was removed it's likely your car's engine still has related factory-installed emissions equipment still in place, namely: smog pump and OE exhaust manifolds with air tubes that come off the top
• the way the smog pump functions is basically as a vacuum that hoovers the denser exhaust gases out of the engine via the air tubes attached to the OE exhaust manifolds, and then blows it down into the catalytic converter via the metal tubing you describe so the cat can do its job
• without a cat present to receive these extra-smelly and smoggy exhaust fumes, they're basically being pumped into the air directly under the passenger seat under a decent amount of pressure

The solution to the problem would be to delete your smog pump using a dummy pully or as described here and:

• cap off the air tubes on the manifolds and other hoses, OR...
• if budget allows get yourself a set of headers and that way you can get rid of all the emissions equipment under your hood for good

For now I'm in the same boat as you and saving up some $$ to get a set of Hedman shorty headers so I can realize a small performance and fuel economy gain and clean up my engine bay at the same time.

Nice looking car you've got btw. What's the name of the color?