Thread: Possible Bad Muffler?

Hi everyone, I recently became a proud owner of a 2005 Grand Prix Base Model with 92k original miles. Love the car, handles like a much smaller car and its got plenty of power and space. Got the car pretty cheap, body engine and tranny are in top shape but the car has many minor issues that I'm fixing slowly over time.
One of these issues may be the exhaust.

I heard they specifically tuned the exhaust system to be loud and sporty on the Grand Prix (even the base model) and the 3800s aren't exactly quiet engines either. At idle the exhaust sounds really good and sporty. However when driving and lightly pressing on the gas pedal at certain speeds and RPMS, particularly on Cruise Control the muffler produces a really low but quite loud rumble, around say 50-55 mph with the RPM being 1600 ish. When accelerating hard the muffler is actually quiet, but when city driving the exhaust is pretty loud, to the point of being somewhat irritating in normal city driving. Maybe I'm just not used to it, I'm 27 and I've only driven 4 cylinder DOHC with 16 valve econobox vehicles and this is my very first V6, and this is an old school pushrod V6 so...

As long as the entire exhaust system is stock then that's just the way it is. If someone changed out the mufflers for something else (Flowmasters, etc..) then it will sound like crap. They came from the factory as quiet as possible to avoid drone at certain RPM's. And these motors don't normally sound any good with any type of aftermarket or "upgraded" exhaust. I've heard a handfull over the years that sound "ok", but your're never going to make it sound great. Just the way it is on these V6's.

Thanks guys for the response. I'll check the resonator, I do believe the exhaust is stock. It's cold here in Canada and they put a lot of salt on the roads in the winter.

One thing though is my dad's 3.5L LZ4 V6 with VVT in his 2008 G6 is nearly as quiet as my 2011 Ford Focus, so that got me thinking something was wrong with my muffler. But the last 3800 my dad had was an '87 Olds 88 and that was a long time ago, so I had no frame for reference for comparison.

I would say its more then likely the resonator, the last year or so i noticed my 07 GP getting louder and finally a couple months ago i decided to have a look. I jacked her up so i could crawl underneath and started her up from cold and looked/ carefully felt around and could feel lots of hot air blasting out the top of the resonator. After spending some time with a grinder and drill bits i removed the flange studs and pulled out the exhaust and after pulling off the heat shield on the resonator i found a big old rusty hole. I decided to put on a metal band-aid with some screws and exhaust sealant for now until i feel like getting it replaced. The band-aid and new flange gasket worked for now shes super quiet again and at idle its hard to tell inside if its even running. the muffler (single exhaust) had no signs of holes or rust.

If it turns out that the resonator is shot like mine was then grab a glasspack and have it welded in. Below is the notes on what I did from research on here:

the glass pack i got was a thrush 24205, it cost 25 bucks. (mine was 32 inch, i cut the inlet tube off and put the flange on there to shorten it up to fit) the flange was $10. i got that at a muffler shop. (no one else carry's them) got a new gasket when i got the glass pack, for the stock cat back flange connection (8 bucks) and then bought 2 new bolts and nuts, cause the old ones always snap off.

You'll want the 2.25 inlet and outlet on the glass pack. if your cat back is the stock welded pipes, you need to cut the old res out, then have the glass pack welded in. you wont need the new flange if it gets welded in. good time to delete the U bend if your car has that. Dynomax exhaust adapter 41806 for glasspack inlet to downpipe.

Its way easier to drop the whole exhaust off the car and then work on it if your going at this yourself. its only held up there by the 2 bolts to the cat, and a bunch of rubber hangers.
if you go to a shop they got a lift to work on.

Originally Posted by FordMan77

If it turns out that the resonator is shot like mine was then grab a glasspack and have it welded in. Below is the notes on what I did from research on here:

the glass pack i got was a thrush 24205, it cost 25 bucks. (mine was 32 inch, i cut the inlet tube off and put the flange on there to shorten it up to fit) the flange was $10. i got that at a muffler shop. (no one else carry's them) got a new gasket when i got the glass pack, for the stock cat back flange connection (8 bucks) and then bought 2 new bolts and nuts, cause the old ones always snap off.

You'll want the 2.25 inlet and outlet on the glass pack. if your cat back is the stock welded pipes, you need to cut the old res out, then have the glass pack welded in. you wont need the new flange if it gets welded in. good time to delete the U bend if your car has that. for glasspack inlet to downpipe.
Dynomax exhaust adapter 41806
Its way easier to drop the whole exhaust off the car and then work on it if your going at this yourself. its only held up there by the 2 bolts to the cat, and a bunch of rubber hangers.
if you go to a shop they got a lift to work on.

I think I have this issue too on an 06 GP base. It isn't terribly loud yet, but getting worse. Inspected the exhaust and didn't find any holes, but I felt some hot air before and after the resonator. It must be coming from under the shield on mine too. Most noticeable on acceleration in low gears. How did you attach the flange to the glasspack? This looks cheap and effective.

Thanks for the info! It's in the shop now getting a new pressure power steering hose but when I get it back I'll feel the exhaust system up when the car is cold and running. I do remember finding it strange at idle that the muffler was pretty quiet but a decent amount of noise was coming from the middle of the car and inside the car I can clearly hear it even at idle but even worse when accelerating at lower RPM (especially around 1500ish). That would make sense it would be the resonator as it literally is right under the seats of the car

@Lanns24- I just had my Dad weld the flange to it and we bolted it all back up. Any exhaust shop should be able to do the same thing for a reasonable price.

Originally Posted by FordMan77

@Lanns24- I just had my Dad weld the flange to it and we bolted it all back up. Any exhaust shop should be able to do the same thing for a reasonable price.

Thanks. There is an exhaust shop near me that should do it for reasonable price.

I've been trying to figure out where the exhaust noise was coming from and this thread pointed in the right direction. I don't have the noise at idle, but it's loud accelerating and under load, pretty quiet otherwise. Definitely coming from under my seats, but no holes anywhere to be found. I did take it to an out of town exhaust shop a few months ago and they put it on a lift and didn't find anything either, so this had me mystified. Definitely getting worse with time though.

Hi all, just an update. Took it yesterday to a local muffler shop, it was indeed the resonator. There was nothing wrong with the muffler itself. Cost $270 Cdn to replace. Car went from a violent ear piercing roar to a smooth sporty sound.

Originally Posted by MercenaryZX

Hi all, just an update. Took it yesterday to a local muffler shop, it was indeed the resonator. There was nothing wrong with the muffler itself. Cost $270 Cdn to replace. Car went from a violent ear piercing roar to a smooth sporty sound.

At that cost, the sealant option posted by TheRiGuy is looking like a viable option. Might take that route once I drop the rear exhaust and see what I'm dealing with.

For $200 USD, I'd say it's worth it to have it done correctly if you plan to keep the car for long term. Otherwise you might get away with doing the patch.

Originally Posted by MercenaryZX

For $200 USD, I'd say it's worth it to have it done correctly if you plan to keep the car for long term. Otherwise you might get away with doing the patch.

I agree that 200.00 isn't terribly expensive, and it would make sense to have it done by a shop, especially if the parts are close that price anyway. However, the patch job would be far less. I don't believe that the only way to have something done correctly is to pay a shop. Sometimes it's worth doing things yourself, not only for cost savings, but for experience and knowledge.

Originally Posted by Lanns24

I agree that 200.00 isn't terribly expensive, and it would make sense to have it done by a shop, especially if the parts are close that price anyway. However, the patch job would be far less. I don't believe that the only way to have something done correctly is to pay a shop. Sometimes it's worth doing things yourself, not only for cost savings, but for experience and knowledge.

Absolutely, provided you have welding equipment and don't mind squeezing under the car if you don't have a lift/ramps.

Originally Posted by MercenaryZX

Absolutely, provided you have welding equipment and don't mind squeezing under the car if you don't have a lift/ramps.

Got ramps. No welding should be required for a patch. Just unbolt the flange and drop it from the hangers.

“Just unbolt the flange”. Good luck with that. Hack saw is your required wrench.


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lol. Your likely correct about that. I'm prepared to hack it off or use angle grinder or another tool to cut it off too.

Complications in your exhaust system can cause your engine to overheat or misfire. A damaged muffler can cause blockages in the system, which result in abnormally high engine temperatures or loss of power. If you suspect you have a muffler issue, turn your car on and let it idle for a few minutes.