Hello all, New here, and I just got a 91 Firebird 305 tbi. I noticed today that the car seemed underpowered, it also has a slight banging sound coming from under the middle of the car at idle. Also the exhaust seems strangely muffled to me, even if it is completely stock. Does this sound like a clogged cat to anybody else? Just looking for second opinions! Appreciate any input.

 

well your story to me sound like its a bad cat. you should crawl under there and hit it with a small hammer(not hard) and if you here rattle bingo.

 

this may be a surprise to you but a 305 tbi only puts out about 170hp. you can make it go fast but stock it looks good. you are moving 3500 lbs with 170 hp so it is slow. you may also need some tuning check the tbi inectors, make sure the computer is the correct one. want to do it fast - spend 100 and have them hook up to the obdI port and do a reading.
try that bang the cat thing and that might be your problem. if not look to see if the trans mount is broken - that bangs from the middle too.
but it will probably still be slow until you find out what is wrong.
and you can make it pretty fast with aftermarket ad ons.
good luck and practice with that search key in the red line.

 

I realize these cars are not that powerful, but I have driven a 91' camaro 305 tbi that was absolutely stock, and a 92 rs 25th ann. that just had very mild bolt ons, they both seemed to have twice as much power. Thanks for the second opinions!

 

glad to help. hope you get it fixed. possibly the computer is not getting the correct imput.
if you look with search you will find a site talking about problem codes and i posted a couple of charts that will allow you to read your OBDI by using a paperclip to get the codes flashed out.
maybe scan for OBDI and paperclip will do it.

 

Well, My cat is almost definitely clogged. I got under there and tapped on it and it almost sounded like the whole internal had shrunk down in one piece and was jumping around.(just a vision I had) I dod have an SES, but I cant check it because I cant find the diagnostic plug! The PO had taken the trim piece under the Steering wheel off and unbolted a bunch of stuff trying to trace down why the Fuel pump wasnt working right, which ended up being just the fuse by the battery. I am sure it is there, I just gotta start putting that stuff back where it goes, and I should come across it. The whole thing just SOUNDS plugged up too.

 

im glad you found the problem. I just replaced my cat with a catco cat and man I can feel the power difference. And picked up 2 extra miles to the gallon sweet.

 

I took the cat off today, and it was pretty rattley. I started it without reconnecting anything(who can resist?) and it idled better, and sounded better in general. Once the pipe was whole again I went for a drive and it really made a difference in power. Still not the way a Firebird should be...Yet. Of course the drive brought a whole other realm of issues to light. Now to the suspension forum...