Alright... The part of my exhast system that is rattleing is right at the cat, it only happens at idle (sounds like a engine knock from the interior, but is NOT an engine knock, it is not comeing for the engine bay) could this be a loose hanger? or could it be the cat it self? if its the cat then how was i able to pass smog with flying colors? The only time the rattle/knock what ever you want to call it is when is jarred (ie: tapping on the pipe with the side of a flash light) I did bottum on on a speed bump once, but i wasnt going more then 3 or 4 mph (i take i slow on speed bumps) i would put this on the exhast forum, but i like to get fellow v6 owners oppions first. Could it be somthing else? (keep in mind it is not an engine knock)

Thanks

Brandon

 

Be careful of when the tech tells you that it passed with "flying colors". Unless your numbers are all right about average, then it's not flying colors. Just don't want you to be one of those people who get their hopes up and have it fail in 2 years, then be telling the tech, "but it passed 2 years ago! What the hell?"

It could be the cat. they rattle when they break loose in the housing. So if you bang on the cat itself, it rattles, right? Just trying to get clarification. Even with a cat that rattles, it might not have turned sideways yet and it'll still work as long as exhaust gas is flowing through it and it's not contaminated.

Something else you might want to check out is the heat shield right above it. It's a two-peice sheild made of aluminum, and it's rivited together, mine made this wierd rattling sound at idle too, then I rivited it back together and the problem was solved.

 

here are the numbers, all were about average or a little above , except for the NO, The rattle happens when either i tap on the cat or the pipe that is leading to the y-pipe(if thats the right term) to the manfolds, when i tap on the pipe i tap right by the cat. Ill check the heat sheild tomaro, i got a few rivits in the tool box and if that doesnt do the trick then i think im start looking for a new cat/mufflar system (since they are 22+ years old, and doesnt look like they have been replaced) dont know if the numbers will help but the car performed better at smog then i though so

And the numbers


For the HC

at 15mph, Max was 135 Mine 23 avg 45
at 25mph Max is 108 mine 21 avg 33

For CO

at 15 mph Max was .97 mine .16 avg .16
at 25 mph Max was .77 mine was .24 avg .14

For NO

at 15 mph Max was 1125 mine was 0654 (a bit high but for the age of the car not bad qoted from the tech) avg 434

at 25 mph Max is 955 mine was 0667 (still, a bit high but for the age not bad quoted from the tech) avg 357

 

Yeah, your numbers are suprisingly good for the age of the cat if it is infact the original. Does your cat look like it has a kind of wire mesh around it or does it have an all aluminum shell?

 

UNtil you get great visual access at the Cat Convertor area, kinda hard to tell what's going on.
Great going that you passed your tests.
That's one aged engine you are working with.
Please not a put down. I had "that engine" in my 1985 Blazer for 211,500 miles until it died.
It could be a strap that hooks exhaust to tranny, too.

 

it doesnt have a wire mesh around the cat, but on the bottom side (the side faceing the road) it looks almost like a wire mesh, the rest of it could be either steel or aluminum i cant tell cause its preaty much all surface rust covering it. if you all need a pic i can go get one.. just got to find some batteries to use

 

Mine was rattling, it was the heatshield on top of the cat. I pulled it off with my bare hand and solved the problem

 

Yeah, I've seen that done, but the passenger doesn't need to wear socks in the winter then.

It's about a foot long, maybe a foot and a half, then yes, that is the factory cat. EWWWW!!!! Probably dead seeing as that it's been in there forever!

 

Yea its the stock cat, could the cat be dead even though the car only as around 75000 miles on it?

 

In your case it's not miles it's previous owners & the years of usage!
I'd plan on changing it

 

what would be the best type of cat to replace it with? a free flowing one? keep in mind im on a college kids budget, cant spend 100's of dollars on a cat.

 

Magnaflow is a good choice. I think that's what Karl put on his 'bird.

 

Yep
Magnoflow!
23494
Used for a 3.4 1995 & it fit perfect my 1985 Firebird set up.
IF I WAS YOU
My first hop up on my 1985 Blazer was a decent Universal CC
I used a 2 1/2" in & out, had the pipes modified by welder for the CC install.
I know I gained some free flow power.
Every little bit helped.
My CC cost me (for the Firebird the Magnoflow) $113 including shipping.

 

2.8 boy.. would this cat be cal legal?(or anybody else that is CAL smog knolegeable)




this cat

 

Any cat is good enough on an OBD-I car (pre-1996)

As long as it's on there, you're good to go.

 

thanks! what size pipes should i be looking at?

 

I'm pretty sure that stock is 2 1/4 inch, but if you want to do a small upgrade while you're at it, you can have the rest replaced with 2 1/2" piping, I think that's the general consensus on a good size pipe for the 6's

 

Summit & Jeg's is source for the Magnoflow CC.