The Official Blown Catalytic Converter Thread

[MSq5]

What symptoms did you get when your flowmaster cats failed? I currently have Flowmaster 200 cells near the transmission and I just did a long road trip (1500 miles) and I noticed my exhaust note has changed. I'm a bit concerned as I have 1500 miles to go to get back home...

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The failure was misfire on the driver side and a metallic rattle in the suitcase muffler. A piece of cat substrate had blown through the Vibrant on that side and into the suitcase. The cat metal was removed. But, it was too late. The engine had lost compression on two cylinders on that bank (hence the misfires). In short, I lost the engine due to excessive back pressure. The cat on that side was blocked completely.


I was able to locate a low mileage replacement complete engine, even including the supercharger and accessories for about $5000. The seller (a salvage yard) didn't know what they had. These go for much more. We were able to sell the accessories and supercharger, even cylinder heads on my old engine and recoup some of the cost. I swapped over the pulleys so I could continue to run the tune. All is well, so far.

There were no symptoms other than misfires and the metallic object in the suitcase muffler. Exhaust tone did not change, although I could understand why it might. We initially thought it was simply an internal baffle in the suitcase, but it was cat material, and the compression test told the sad news.

I did not have any change in sound other than that rattle. The only sign was the misfire on one cylinder. Compression was zero on that one and 70 on the other. These were cylinders 4 and 5.

Try to baby the car until you get home. I would not do any full throttle pulls. If it starts misfiring, I would park it and try to save the engine, but it could be too late. The best solution would be to find a muffler shop and get the Flowmasters out, even if it means temporarily installing a section of straight pipe where they are connecting to your resos, then put ceramic cats in.

I made a huge and costly mistake with the Flowmasters. Steel just separated and clogged. If ceramic fails, it is more likely to break up and get blown out. If you relied in my advise or the parts listed in my signature regarding the Flowmasters, I deeply regret it.

Subsequently, I did a deep research dive on the Flowmaster 200 cell steel bottle carsvand discovered an alarmingly frequent failure rate.

[Twi7ch]

The failure was misfire on the driver side and a metallic rattle in the suitcase muffler. A piece of cat substrate had blown through the Vibrant on that side and into the suitcase. The cat metal was removed. But, it was too late. The engine had lost compression on two cylinders on that bank (hence the misfires). In short, I lost the engine due to excessive back pressure. The cat on that side was blocked completely.


I was able to locate a low mileage replacement complete engine, even including the supercharger and accessories for about $5000. The seller (a salvage yard) didn't know what they had. These go for much more. We were able to sell the accessories and supercharger, even cylinder heads on my old engine and recoup some of the cost. I swapped over the pulleys so I could continue to run the tune. All is well, so far.

There were no symptoms other than misfires and the metallic object in the suitcase muffler. Exhaust tone did not change, although I could understand why it might. We initially thought it was simply an internal baffle in the suitcase, but it was cat material, and the compression test told the sad news.

I did not have any change in sound other than that rattle. The only sign was the misfire on one cylinder. Compression was zero on that one and 70 on the other. These were cylinders 4 and 5.

Try to baby the car until you get home. I would not do any full throttle pulls. If it starts misfiring, I would park it and try to save the engine, but it could be too late. The best solution would be to find a muffler shop and get the Flowmasters out, even if it means temporarily installing a section of straight pipe where they are connecting to your resos, then put ceramic cats in.

I made a huge and costly mistake with the Flowmasters. Steel just separated and clogged. If ceramic fails, it is more likely to break up and get blown out. If you relied in my advise or the parts listed in my signature regarding the Flowmasters, I deeply regret it.

Subsequently, I did a deep research dive on the Flowmaster 200 cell steel bottle carsvand discovered an alarmingly frequent failure rate.

Oh man this is not the news I wanted to read. When you were getting misfires did you get get a flashing CEL or EPC light? Or was it just a loss of power when accelerating?

Also did it log any misfire codes? I just scanned with obd11 and I'm not seeing any misfires detected. Sadly obd11 doesn't show me live data of misfires.

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[MSq5]

Oh man this is not the news I wanted to read. When you were getting misfires did you get get a flashing CEL or EPC light? Or was it just a loss of power when accelerating?

Also did it log any misfire codes? I just scanned with obd11 and I'm not seeing any misfires detected. Sadly obd11 doesn't show me live data of misfires.

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Misfile and cylinder deactivation codes consistently on two cylinders on the driver side bank. Yes, an EPC light. I can't say you are safe if you don't get those warnings, but I did in addition to the rattle in the suitcase muffler.

[Twi7ch]

Misfile and cylinder deactivation codes consistently on two cylinders on the driver side bank. Yes, an EPC light. I can't say you are safe if you don't get those warnings, but I did in addition to the rattle in the suitcase muffler.

I just took it for a small drive and hit 4500k RPM. 1 misfire in Cyl 5 & 6. It's going to a shop tomorrow.

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[Twi7ch]

Little update. Had the car compression tested and it came back all good with 165-175 PSI. The mechanic banged on the HFC and didn't hear any noise, he thinks new spark plugs will resolve the problem and a new O2 sensor but I'm skeptical since this O2 sensor has always thrown a slow read code. And I can't see that being why I the exhaust note changed and multiple misfires. Anyways, I'm having these flowmasters removed regardless for peace of mind. I really don't want to spend money on GESI cats next. The amount of money I've had to piss away on this exhaust system is a bit outrageous and I'm not even dual pulley.

[Twi7ch]

I saved my motor! Flowmaster 200cell cats failed in the downpipes. I'm thankful I was able to get this resolved as quick as I did while on a road trip. Now I can drive the 1500 miles back home with peace of mind.

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[Slvrbul8]

The amount of money I've had to piss away on this exhaust system is a bit outrageous and I'm not even dual pulley.

I feel ya! I just had the GAS high flow cats installed after my oem cats started throwing low efficiency codes. One side was completely blown out, the other partially. Combined with all the issues I've had with my milltek catback and i wish I never messed with the stock exhaust.

Advice to anyone new to this platform...leave the exhaust alone, haha

[knock.out]

I feel ya! I just had the GAS high flow cats installed after my oem cats started throwing low efficiency codes. One side was completely blown out, the other partially. Combined with all the issues I've had with my milltek catback and i wish I never messed with the stock exhaust.

Advice to anyone new to this platform...leave the exhaust alone, haha

Thanks for sharing, GAS claims ZERO failures of their gesi cats in stock location. Did you have the 400cel gen 2 gesi or 300cell gen 1?



B8.5 S4 DSG
034 stage 2+
previous: B6 A4 Ultrasport 6MT

[Fresh.S4]

That claim of "hundreds" of setups is so wild, especially those power numbers. Especially when it's very hard for the average user to break 500whp.

If y'all remember redstars from years back. They were the go to catted downpipes and it didn't take very long for folks to blow out those same gesi's in the same location and those guys def weren't pushing power numbers like that.

They do look really good though 😍

[knock.out]

That claim of "hundreds" of setups is so wild, especially those power numbers. Especially when it's very hard for the average user to break 500whp.

If y'all remember redstars from years back. They were the go to catted downpipes and it didn't take very long for folks to blow out those same gesi's in the same location and those guys def weren't pushing power numbers like that.

They do look really good though

Exactly my thought, it's a fundament flaw in the design that material science can't solve for a reasonable cost.

I have P042000 code now at 1.7k rpm and P030300/P030200 cyl 2/3 misfire at about 6k rpm. Coils and plugs are 1yr old, so planning to check IC cores and injectors first. If blown cat I'm considering doing headers to downstream exhaust cutouts then cats.

Seems like a good way to let it rip on track with no impact to cats. Witht cutouts, then also able to close it up any baby the cats for daily/spirited driving.

Has anyone run this setup?



B8.5 S4 DSG
034 stage 2+
previous: B6 A4 Ultrasport 6MT

[Nillious]

I wonder what it is about these motors that is so hard on cats. From what I've always known it's overly rich fuel mixture that's melts cats. Maybe take this time to replace your upstream O2 sensors. If they are not reading correctly it can cause a rich mixture all the time. Make sure you're misfire counts are low. Lots of misfiring can load them up with fuel and melt them as well.

[Slvrbul8]

Thanks for sharing, GAS claims ZERO failures of their gesi cats in stock location. Did you have the 400cel gen 2 gesi or 300cell gen 1?



B8.5 S4 DSG
034 stage 2+
previous: B6 A4 Ultrasport 6MT

Bill said they are only using the Gesi 400 gen 2 now. The craftmanship was really good and the installer said they fit just like factory. The sound is a little deeper and more gravelly than oem.

[ThoseRings]

I saved my motor! Flowmaster 200cell cats failed in the downpipes. I'm thankful I was able to get this resolved as quick as I did while on a road trip. Now I can drive the 1500 miles back home with peace of mind.

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Good catch!!!

I wonder what it is about these motors that is so hard on cats. From what I've always known it's overly rich fuel mixture that's melts cats. Maybe take this time to replace your upstream O2 sensors. If they are not reading correctly it can cause a rich mixture all the time. Make sure you're misfire counts are low. Lots of misfiring can load them up with fuel and melt them as well.

My car with the stock tune will do a small puff of black when I rip on it. My understanding is that stage 1 tunes, especially APR run even richer.

[Slvrbul8]

If y'all remember redstars from years back. They were the go to catted downpipes and it didn't take very long for folks to blow out those same gesi's in the same location and those guys def weren't pushing power numbers like that.

The current gesi 400 cell gen2 has a completely different core than the old redstars used. The dual wound s-core is the game changer.

[Twi7ch]

The current gesi 400 cell gen2 has a completely different core than the old redstars used. The dual wound s-core is the game changer.

Do you think Gesi OBD2 (300 Cell) could handle the temps in the same spot my flowmasters were (in the downpipes right at the bend before it goes into the first resonators)?

[Slvrbul8]

Do you think Gesi OBD2 (300 Cell) could handle the temps in the same spot my flowmasters were (in the downpipes right at the bend before it goes into the first resonators)?

Hard to say for certain, but I think the gesi would be better quality than the flowmasters.

[STXA7]

Do you think Gesi OBD2 (300 Cell) could handle the temps in the same spot my flowmasters were (in the downpipes right at the bend before it goes into the first resonators)?

“the definition of insanity is doing the same thing over and over and expecting different results”

as someone mentioned before , every inch you move it downstream will protect the hfc core

JHM HFC placement go where original pair of first resonators are at maybe try copying that placement

[Twi7ch]

“the definition of insanity is doing the same thing over and over and expecting different results”

as someone mentioned before , every inch you move it downstream will protect the hfc core

JHM HFC placement go where original pair of first resonators are at maybe try copying that placement

I already have a Gibson resonator in that location otherwise I would. Sadly the only spot I have room is where my last pair of cats were. If GESI aren't likely to survive I guess I'm SOL

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[Slvrbul8]

I already have a Gibson resonator in that location otherwise I would. Sadly the only spot I have room is where my last pair of cats were. If GESI aren't likely to survive I guess I'm SOL

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You are not sol, you just need to get the 400 cell version. https://garageautosports.com/product...0&_ss=e&_v=1.0

[Twi7ch]

You are not sol, you just need to get the 400 cell version. https://garageautosports.com/product...0&_ss=e&_v=1.0

I can't justify dropping $2g's on those as much as I'd like to have them.

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[Fresh.S4]

I already have a Gibson resonator in that location otherwise I would. Sadly the only spot I have room is where my last pair of cats were. If GESI aren't likely to survive I guess I'm SOL

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you can CLEARLY fit hfc's right after the tp and have room to stick resonators...

https://www.audizine.com/forum/showt...1#post15131506

[Twi7ch]

you can CLEARLY fit hfc's right after the tp and have room to stick resonators...

https://www.audizine.com/forum/showt...1#post15131506

This is where I had my flowmaster HFC so yes there is room after the TP. I'm just saying I don't have room to place them further away from the engine than that.

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[Fresh.S4]

just get some magnaflow's or if you want to spend the extra $$ get some gesi cats in the same location.
i thought about getting that gibson resonator but its all baffles and no packing. not sure how the sound would of turned out.

[Twi7ch]

just get some magnaflow's or if you want to spend the extra $$ get some gesi cats in the same location.
i thought about getting that gibson resonator but its all baffles and no packing. not sure how the sound would of turned out.

The Gibson does have a bit of a hollower sound but it's the only thing that's lasted. I blew out my MF res, I blew out my Borla res. This at least helps with rasp and is holding up.

[STXA7]

just get some magnaflow's or if you want to spend the extra $$ get some gesi cats in the same location.
i thought about getting that gibson resonator but its all baffles and no packing. not sure how the sound would of turned out.

Check out YouTuber C Midas he has a video specifically about the Gibson muffler with before and after sound on his A6 3.0t not sure if he has any hfc though probably not.


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[Fresh.S4]

Check out YouTuber C Midas he has a video specifically about the Gibson muffler with before and after sound on his A6 3.0t not sure if he has any hfc though probably not.


Sent from my iPhone using Audizine Forum

yea i know him. hes local.

i originally started with polo performance (helmz holtz) but after adding tps, it was a downhill losing battle with having to add hfc's and multiple sets of resonators. if my current 5" cans ever blow out, ill probably try the gibson just for shits and giggles.

[Nillious]

I wonder what a set of super 50s would sound like on these cars. Zero packing and can never blow out. They are pretty damn quiet on the cars I’ve heard with them but they were all v8 or na v6s

[M1k3ee]

I have had no issues with the GESI GEN 2 cats placed in the resonator section in the past three years at stage 2 power level. This includes one German autobahn trip (>155 mph+) and frequent 60 - 120 mph pulls. Quite interesting to see that other vendors claim they also hold up at stage 2+ level when placed in the stock cat location.