I read several posts about exhaust sound, but it just doesn't answer my question.

I have had my 1987 GT for 14 years. Stock exhaust. Love the exhaust note. I bought an 88 GT in April. The very first time I drove the car I told myself I have to fix that exhaust leak. The exhaust sounds nasty!

I finally took the car by an exhaust shop to have it diagnosed. The guy could not find an exhaust leak at all. I ook the car home and got under it looking for a sign of an exhaust leak. Nothing.

The exhaust sounds ratty. Like a blown muffler. Sounds reasonable at idle and mild acceleration, but real ratty when under hard acceleration.

Can the guts of a muffler go bad? Or could it be the cat. converter?

It could be either or both, clogged or broken, though it's hard for anyone to say without hearing it.

Mine had a couple small cracks on the outside wall (it's double walled) that grew until the outside wall would rattle against the inner wall. Plus if you shook it you could hear little pieces rolling around inside. The cat had previously disintegrated. The net effect was a loud, rattling exhaust.

Hey guys,

Thanks for the replies. Although my cat sounds loose a bit inside, the sound is that ratty (not rattly) sound. Almost as nasty as a straight six, no muffler, just a straight pipe. By your replies should I assume that the sound between the 87 and 88 should be the same?

[This message has been edited by sjmaye (edited 10-20-2007).]

Yes, the 2.8 Liter V6 didn't really change in 1988, so the exhaust note would be the same, as far as stock exhaust goes. If you do get around to replacing the exhaust system, I would get an Ocelot exhaust system, it sounds great. But if you want loud and throaty put West Coast Fiero's Flowmaster 40 Series muffler on it.

Everything is stock. The standard stock sound is fine by me. I sure hate to think I would either have to replace the whole exhaust. I don't even like the thought of cutting the muffler off to replace it.

Your opinions- What's the chance of the problem being catalytic converter vs. the muffler?


PS- The exhaust sound is NOT the muted sound of a plugged cat. At least I don't think so.

Does you exhaust sound like a hissing sound?

If it' a "ratty" sounds rather than "rattly", I'd have to guess the muffler over the cat. The cat usually gets plugged or the bricks break up and rattle, but I've seen some mufflers that came apart internally causing funky sounds. Anything's possible on a 20 year old car.
Hope you get it fixed up soon.

Nope, no hiss. Almost the quality of tone of no muffler.

Your Muffler is shot then. It probably would be easier to cut out the muffler and replace it with something else. What ever you do DON'T go to the parts store and buy a factory replacement, they don't sound the same, they are much quieter. Either get one from the Fiero Store or buy a Spintech one from West Coast Fiero, they spintech muffler has a more aggresive sound to it. Or you can just replace the intire exhaust system, but you can only buy a cat back, unless you want to buy a new cat. If that exhaust system is the original system then I wouldn't doubt that the muffler is gone in it. If it was hissing then it would be the cat plugged up. It shouldn't be too hard to replace that muffler, since that car is a southern car and there is no rust, I used to live in Nashville, so I know what cars are like down there. Now that I live in Maine I invested in a completly stainless steel exhaust system, everything from header to bolts to clamps, all stainless steel. Even though I don't drive it in the winter.

quote Originally posted by craigsfiero2007:It shouldn't be too hard to replace that muffler, since that car is a southern car and there is no rust, I used to live in Nashville, so I know what cars are like down there.

Oh, how I have learned of the infamous Northeastern cars and rust. Man you guys have it rough! I bought this car from a guy in Rhode Island. Holy Cow! I have had it since April and spent the majority of the time de-rusting and rust-proofing (POR15) it. I have it done from the front to the rear sub-frame. What a pain. I am counting my blessing it was generally surface rust albeit a lot of it.

Other than the sound, the exhaust is in good shape. I guess it is the OEM stainless 304(?). Surface rust only. Very solid. I broke free the two bolts going to the y-pipe yesterday. I wanted to be sure I can get the system down easily when I drop the rear sub-frame in November. More POR15.

I don't see any stock mufflers on the Fiero Store. You wouldn't by chance of the GM part number would you?

[This message has been edited by sjmaye (edited 10-20-2007).]

quote Originally posted by sjmaye: Oh, how I have learned of the infamous Northeastern cars and rust. Man you guys have it rough! I bought this car from a guy in Rhode Island. Holy Cow! I have had it since April and spent the majority of the time de-rusting and rust-proofing (POR15) it. I have it done from the front to the rear sub-frame. What a pain. I am counting my blessing it was generally surface rust albeit a lot of it. Other than the sound, the exhaust is in good shape. I guess it is the OEM stainless 304(?). Surface rust only. Very solid. I broke free the two bolts going to the y-pipe yesterday. I wanted to be sure I can get the system down easily when I drop the rear sub-frame in November. More POR15.

Yeah, I got lucky, my Fiero GT lived in South Carolina most of it's life, so it has no rust at all. But my daily driver (S-10), you just touch the frame rail and you got like a pound of rust right in your eye. I miss working on southern cars, it's nice and less frustrating and cheaper, if you look at the amount of money it costs to replace the stuff you broke trying to remove something. I think the stock exhaust system might be 304 stainless, not sure though. Your lucky that your Fiero only has surface rust, get under a real northern daily driver, it seems ever bolt you turn breaks off. It's not very fun and makes working on cars very very very frustrating. POR15 is good stuff. I used that on a Camaro I had. I have got to get some Rhino lining to undercoat my Fiero GT with.

I looked up the stock muffler on MonsterPartsOnline. ~$230! I might have to get over the sound. Ear plugs are cheaper.

Here is a link to some on West Coast Fiero, the Spintech one sounds great but is a little more aggresive than stock.
http://www.westcoastfiero.com/exhaust/muffler.html

Does it still have the original catalytic converter? How about your 87? The cat will make a MAJOR difference in exhaust sound. When my cat plugged up, I put on a straight pipe temporarily, and the engine sounded good at idle, but that was about it. The rest of the time it sounded like a UPS truck. When I put on a new aftermarket converter, the note changed, but was still slightly louder than stock. (hard to compare against the bad converter, though).

If there are no holes in the muffler, I'm not sure what would blow out in it. I don't think it's got any packing material - just baffles, so it would require physical damage. It shouldn't "blow out" like old glass packs would. I've still got the OEM muffler on my Formula, with 175k miles - and several backfires.

Did the exhaust shop check the manifolds for cracks, or just the pipes?

quote Originally posted by Formula88: Does it still have the original catalytic converter? How about your 87? The cat will make a MAJOR difference in exhaust sound. When my cat plugged up, I put on a straight pipe temporarily, and the engine sounded good at idle, but that was about it. The rest of the time it sounded like a UPS truck. When I put on a new aftermarket converter, the note changed, but was still slightly louder than stock. (hard to compare against the bad converter, though). If there are no holes in the muffler, I'm not sure what would blow out in it. I don't think it's got any packing material - just baffles, so it would require physical damage. It shouldn't "blow out" like old glass packs would. I've still got the OEM muffler on my Formula, with 175k miles - and several backfires. Did the exhaust shop check the manifolds for cracks, or just the pipes?

The cat appears to have been changed as the one there is not welded in place. The ceramic (or whatever) inside is loose, just like my 87's was a couple times. I don't think there is any chance the muffler or cat is plugged. First, I know the muted sound of plugged. This sounds open. Just too open. Second the engine power is very good.

Since the cat is clamped in place I could take it out and replace it with a straight tube just to try. I might try that when I have the exhaust out and subframe down.

Are you convinced the "ratty" sound is coming out of the exhaust tips? Mine was a little raspy. When I pulled the engine for a swap the #2 exhaust pipe bend was broken free from the flange and there was a good size gap there.

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1988 GT, 5-speed, white, beechwood leather, 3.4 DOHC 6-speed installation in process. Really. I am working on it.

quote Originally posted by sspeedstreet: Are you convinced the "ratty" sound is coming out of the exhaust tips? Mine was a little raspy. When I pulled the engine for a swap the #2 exhaust pipe bend was broken free from the flange and there was a good size gap there.

Not really sure. The muffler shop guy hunted around the exhaust manifold with a piece of rubber tubing in his ear listening for exhaust leaks and found nothing. In looking at the rest of the exhaust I see no signs of leaks, but I can not see it all as the muffler is tucked up in the pocket.

quote Originally posted by sjmaye: The cat appears to have been changed as the one there is not welded in place. The ceramic (or whatever) inside is loose, just like my 87's was a couple times. I don't think there is any chance the muffler or cat is plugged. First, I know the muted sound of plugged. This sounds open. Just too open. Second the engine power is very good. Since the cat is clamped in place I could take it out and replace it with a straight tube just to try. I might try that when I have the exhaust out and subframe down.

You could take off the cat and break up the ceramic honeycomb inside so that it completely comes out. That stuff tends to break up and clog at the worst possible time. It just keeps bumping around until it's just small enough to wedge in the pipe to the muffler.

Check the headers where the short stubs are welded into the main tube - you probably have one thats cracked.
You have to look very carefully, maybe even use a piece of wire as a probe, because it's many times very hard to see.
Usually if you pull off the cat and run the original muffler, the sound is great!

The front manifold cracks badly where the #4 and #6 cylinder tubes are welded to the main tube, those cracks make it sound like a classic exhaust leak. Another source of cracks and leaks is the Y-pipe where the front and rear bank pipes join, but you have to open up the heat shield wrap to see that.

JazzMan

My 88 3.4 (already louder than stock, due to a big cam, headers, and no cat) suddenly had a drastic change, for the worse, in its exhaust note.
Imagine a "blaaaaaaaat" sound, whenever the engine was under load.

I took off the stock system and replaced it with an Ocelot system. It's still loud as hell, but it doesn't sound like an airplane any more.

Afterwards, someone mentioned that the stock muffler is two layers, and that the inner layer might be rattling against the outer layer.
He suggested that a sheet metal screw, in the middle of the "flat" side of the muffler, might help.

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Raydar
88 4.9 Formula IMSA Fasback..........................88 3.4 coupe -soon to be something other than red

Read Nealz Nuze! Praise the Lowered!

[This message has been edited by Raydar (edited 10-20-2007).]

quote Originally posted by Raydar: Imagine a "blaaaaaaaat" sound, whenever the engine was under load.

Closest explanation to my sound. I am going to pull the exhaust.

I worked on my exhaust for 3 days and finally figured it all out. I was going to put a stock gt muffler on, until I couldnt get it to fit. I have a 3.1 form a Lumina, so the exhaust exits on the backside of the engine, giving you a lot less room to work with. Anyway, I managed to get a downpipe connected to the muffler, and with it all welded up the car sounded like a V6 chainsaw. I shook the muffler afterwards and heard a bunch of loose rust inside of it. I'm sure the muffler was probably rotted out, and man did it sound like crap. Before that, I had a single inlet/outlet muffler form autozone. It was cheap and made my car sound like a stock Lumina. I finally ended up just welding a cat in place of the downpipe, and had it Y at the bottom and ran it to the exhaust tips. Its loud, but hopefully not loud enough to get in trouble. it sounds a lot better than the stock GT muffler did though. So I'm guessing your muffler is probably rotted out. If the cat was plugged, your car wouldnt run worth a crap, so I would look into the muffler for sure. Also, check to make sure your exhaust isnt vibrating against the cradle or body.

quote Originally posted by toadson: So I'm guessing your muffler is probably rotted out. If the cat was plugged, your car wouldnt run worth a crap, so I would look into the muffler for sure.

My curiousity got the best of me. i took the exhaust out. Here it is:

Pretty rusty, but solid. The muffler has not holes or rusted out areas, but the seam is raised a bit


I decided to reinstall it while I decide what I want to do with it. It may be nasty sounding, but it drives.
I managed to get a picture of what I thought was the GM part number-

Does nto come up on MonsterParts

WRT- The OEM GM muffler mentioned above. For ~$230 would I be getting the mufller, 304 SS tubing to the cat and the exhaust tips? Sounds better when thinking of it that way.

I will check Monster Parts in the Mall.

The muffler I installed wasn't rusty at all on the outside. There were no holes or anything in it, but I could hear a bunch of loose junk inside. You ought to try hitting the muffler and cat with a rubber mallet, just to see if you hear anything inside of them. I guess its possible for the cat to be broken up, but if the broken pieces havent turned sideways then your car would still run alright.

Go with a Spintech. It will fit in the tight Fiero exhaust space and the sound is amazing. You'll be very happy that you did.

Guys,

I had another thought. Just how much impact is the catalytic converter to the exhaust sound?

When I had the exhaust out I remember the chunk of whatever inside the cat was loose and rattling. In fact I got the impression it was fairly broken up.

I ignored this becuase of several posts talking of gutting it. Can the cat condition have a significant impact on the exhaust sound?

The cat acts as a "pre" muffler in that it does quiet the exhaust down a bit. Currently I'm running only a turbo and a cat, no muffler at all and it isn't that loud until you get on it.

A final thought before I drop my engine. That nasty sounds seems to be coming from right behind the drivers seat. Any chance this is a cracked exhaust manifold?