Hi all:
I have a 2005 S-Type, 4.2 V8
I was on the highway and my CEL reported a coil failure in Cylinder #2. I was about 40 miles from home and limped home carefully, but by the time I got home my exhaust sound like a truck. I am not sure, but I think some raw gas got dumped into the exhaust system during the drive home and either burnt up the fiberglass in the resonators or blew a baffle int he mufflers. A new exhaust system is astronomically expensive so I want to replace only what is bad.
The coil has been replaced and the engine seems to be running fine.
Has anyone had this experience? Can anyone answer my questions?
1) Did you find the problem was the resonators or mufflers?
2) Will it damage the engine to drive with reduced back pressure?
3) Would I replace both Mufflers or resonators or just the ones on the #2 cylinder (passenger) side?
3) Should I buy new or used?
Thank you,
Jeff

 

At any point in this brouhaha, was the CEL flashing? That's designed to get your attention because catalyst damage is likely happening. When the light is on steady, that's a medium level problem that will need attention soon. But if the light is flashing, that's a high priority problem that needs attention immediately before damage occurs, in other words pull over as soon as safe to do so and do not continue driving.

Do you have any fault codes currently? P0420 or 0430 are the likely ones, indicating reduced efficiency from the cats. These are what you can expect to see if the cats had overheated due to a misfire.

I wonder if one of the cats broke apart internally. The noise you're hearing may be chunks of the cat matrix rattling around. These chunks may still be inside the cat shell, or they may have blown back to the muffler.

On my '02, I've been nursing a marginal cat for years, with a sporadic P0420 code about 5% of the time. Last month the car started making a horrendous racket, and faulted P0420 on every drive cycle. It was really hard to isolate the noise. At one point it seems to be coming from one of the serpentine belt pulleys. Finally the noise got loud enough that I could tell it was somewhere in the exhaust. I could hear the car about two blocks away. Sounded like a dump truck. Then suddenly the noise stopped, which I think was the matrix chunks finally breaking into smaller pieces and exiting the exhaust.

That's my hunch what has happened to your car.

 

Oops, forgot to mention an important detail about the noise. It was fairly quiet at idle. I think was because airflow was low and the chunks just sat there.

Above 1800 RPM or so, it quieted down. My hunch was the high airflow pinned the chunks in place so they didn't rattle.

Above idle up to 1800 was the loudest. I think there was enough airflow to blow the debris around, but not enough to pin it in place.

 

Hi,
There are no Fault Codes, only P1111. I also had my car inspected and it passed the Massachusetts Emissions test with flying colors, bit they failed me on the excessive noise of the exhaust. They thought at first there was a leak in the front pipe, but there is no leak. Just a loud exhaust noise.
During my drive home the CEL light did flash several times and then went solid, so I kept going. That is what I did wrong. I should have stopped immediately, but it was not continuously blinking, so I kept on driving home.
The next day I drove the car to a mechanic about 30 miles away for repair of the coil. Everything seems to be working fine now except the loudness of the exhaust.
I am concerned that if it is the Catalytic Converter and I start replacing mufflers and resonators a great expense then I waste a lot of money and don't fix it.
If I replace the Catalytic Converter only and that doesn't fix it then I again waste money.
Thanks,
Jeff

 

There are tests for cats, such as removing O2 sensors and using a borescope or checking with an IR gun.

 

Not really sure what to suggest. I can only state that tracking down the source of a noise can be very difficult at times. I've had a Steelman Engine Ear 65001 for many years and recommend it without reservation. The microphone is highly directional:

https://www.steelmantools.com/engine...ethoscope.html


In your situation, you may just want to take the car to a muffler shop and get their opinion and an estimate.

 

I think the op is right in thinking raw fuel was getting into the cat because of the bad coil.....then it ignited and boom....possibly even in the muffler....fully agree for muffler shop time and converter diagnosis before any actual exhaust work

 

Did you ever get the exhaust noise resolved