# What causes catalytic converter to fail **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mustang, ford\ **Created:** [August 21, 2021, 2:40am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859 "2021-08-21T02:40:42Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [August 22, 2021, 4:27am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/21 "2021-08-22T04:27:46Z")
I’m thinking you may be right…is fixing the header leak as simple as tightening the all the bolts? Or will i have to remove/install them again? ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [August 22, 2021, 11:49am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/22 "2021-08-22T11:49:47Z")
Header leaks… I sure would start with the bolts first! Blocking the tailpipesat idle can identify leaks… leaks will make a big hissing sound. Attempt 2 would be… If it blew out the gasket you’ll have to replace it. Worst case step 3 would be… Remove the header and have a machine shop flatten the mating flange or weld up a pinhole. ---
**Author:** ![FoDaddy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/fodaddy/32/717_2.png) [@FoDaddy](https://community.cartalk.com/u/FoDaddy)\ **Post date:** [August 22, 2021, 9:19pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/23 "2021-08-22T21:19:23Z")
I think you’re onto to something. My tuner flat refuses to use anything but OEM gaskets for header installs. Even if the headers come with gaskets, if they aren’t the OEM gaskets he won’t use them. I wonder if the OP used aftermarket gaskets. If the gasket is leaking that would explain what’s going on. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [August 22, 2021, 9:28pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/24 "2021-08-22T21:28:27Z")
> [@FoDaddy](#): > > My tuner flat refuses to use anything but OEM gaskets for header installs I have blown out more than a few “Mr Gasket” style fiber gaskets…on race engines with very limited mufflers - so virtually no backpressure. The OE style metal-over-fiber style hold up very well. They were the ones I’d use, too. I think the dead-soft copper gaskets may be a good choice but I have not tried them. ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [August 22, 2021, 9:32pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/25 "2021-08-22T21:32:34Z")
My mechanic that installed the headers actually called me and told me the gaskets that came in the bbk kit suck and he was gonna clean use the original metal gaskets. The kit also didn’t come with enough bolts so he reused the ones off the original headers. I tried blocking the tailpipes and I hear a very faint clicking coming from the engine bay but i’m not sure if it’s an exhaust leak and to be fair most engines have a slight ticking. It doesn’t get louder when revved. I was gonna call MPT tomorrow and datalog just to eliminate the slim chance that the tune wasn’t written correctly. I am getting very harsh downshifts, backfires and the car not going below 2k rpms when downshifting (kinda stalls at 2k and won’t go lower unless i brake). Not sure if this is how a 93 prx race tune from mpt is supposed to be behave but I think i’ll datalog to eliminate a bad tune being the issue before digging into anything else and spending money on diagnostic or throwing more parts ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [August 22, 2021, 9:35pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/26 "2021-08-22T21:35:02Z")
> [@J162\_165342](#): > > Not sure if this is how a 93 prx race tune from mpt is supposed to be behave I am pretty confident this is not how that tune is supposed to work! Mine doesn’t work that way! Bama Tune in a’13 GT automatic ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [August 22, 2021, 9:36pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/27 "2021-08-22T21:36:38Z")
Man i had bama before with no problems but so many people on the internet are raving about how much better MPT is so thought i’d try it but i’m not sure now lol ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [August 23, 2021, 1:33pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/28 "2021-08-23T13:33:09Z")
There have been THOUSANDS (or even tens of thousands) of catalytic convertors replaced over the years when it was just a faulty O2 sensor. ---
**Author:** ![Cavell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cavell/32/43396_2.png) [@Cavell](https://community.cartalk.com/u/Cavell)\ **Post date:** [August 23, 2021, 2:22pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/29 "2021-08-23T14:22:53Z")
I’ve been watching engine masters lately as they like to compare minor changes to determine affect on hp/torq over the rpm range. I bet headers on a small displacement v6 result in loss of torq under 4500 rpm. Might even influence drive ability. ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [August 23, 2021, 4:29pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/30 "2021-08-23T16:29:37Z")
I was wondering about that too. The stock manifolds weren’t really restrictive. ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [August 24, 2021, 6:38am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/31 "2021-08-24T06:38:02Z")
Holy s@!& guys i think i might have found the answer. Would appreciate if someone could clarify the following: Originally to try to fix the p0420 code i had an exhaust shop replace the passengers side cat converter. This was a few days ago I’ve been driving my car for a few days since they replaced the cat and noticed my car sounded noticeably raspier especially at higher rpms than before, even though they used an OEM cat on the side they replaced. I thought this was strange because I never made any other changes to the exhaust yet it sounded much louder than before and raspier and even though the code was gone and the car definitely ran better, something still felt a bit off when driving it (mostly a very small misfire/stuttering from exhaust when decelerating and slight loss of low end power.) Turns out, ford put small bottle resonators on both sides JUST before the cat. I looked under my car and noticed the passenger side of the car that had the cat replaced was missing the resonator! The shop probably sawed it off when replacing the old cat and just put a regular pipe in place…to be fair they’re really difficult to differentiate, they almost look like straight pipe unless you look very closely Anyway, could one side of the car having a resonator and the other not having a resonator make the cars acceleration slower, cause backfires and/or misfires? Due to each exhaust bank having a different amount of backpressure? If so I think I may have just found my problem and i’ll take it back to the exhaust shop tomorrow. This makes sense to me but if it doesn’t to you all let me know. Don’t wanna spend any more than I need to. ---
**Author:** ![Cavell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cavell/32/43396_2.png) [@Cavell](https://community.cartalk.com/u/Cavell)\ **Post date:** [August 24, 2021, 12:14pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/32 "2021-08-24T12:14:58Z")
a “resonator” before the cat? ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [August 24, 2021, 1:03pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/33 "2021-08-24T13:03:54Z")
Oh i meant the resonator is after the cat not before ---
**Author:** ![Cavell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cavell/32/43396_2.png) [@Cavell](https://community.cartalk.com/u/Cavell)\ **Post date:** [August 24, 2021, 1:38pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/34 "2021-08-24T13:38:16Z")
I could see some high rpm gain with headers. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [August 24, 2021, 11:15pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/35 "2021-08-24T23:15:55Z")
The interaction of the exhaust system w/the rest of the engine is pretty complicated. So it is quite possible your _missing resonator_ theory is correct. For example Google “exhaust scavenging” . ---
**Author:** ![FoDaddy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/fodaddy/32/717_2.png) [@FoDaddy](https://community.cartalk.com/u/FoDaddy)\ **Post date:** [August 25, 2021, 12:21am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/36 "2021-08-25T00:21:11Z")
Wouldn’t have Y pipe, 2011+ V6 Mustangs have dual exhaust. I want to say they come from the factory with a X pipe. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [August 25, 2021, 1:28am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/37 "2021-08-25T01:28:59Z")
I want to say they have a factory H pipe like the V8s… and that missing resonator is unlikely your problem unless the cut off portion is leaking. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [August 25, 2021, 1:42am UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/38 "2021-08-25T01:42:35Z")
AP/Eastern with resonators; ![image](https://global.discourse-cdn.com/cartalk/original/3X/7/2/72cccd07943ef1fa2ba501cc345ade8af17c83bc.png) Walker without resonators; ![image](https://global.discourse-cdn.com/cartalk/original/3X/6/0/603ae71ece6dc45df56bfebb29913a61abc9b5d3.jpeg) ---
**Author:** ![Scrapyard-John](https://avatars.discourse-cdn.com/v4/letter/s/f6c823/32.png) [@Scrapyard-John](https://community.cartalk.com/u/Scrapyard-John)\ **Post date:** [August 25, 2021, 4:44pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/39 "2021-08-25T16:44:47Z")
I don’t think the missing resonator is going to come into play (other than sound), especially since it’s past the 02 sensor in the exhaust stream. Sounds to me like the issue is going to be with the headers (leaking) or with the tune not accounting for the headers. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [August 25, 2021, 9:54pm UTC](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859/40 "2021-08-25T21:54:01Z")
> [@Scrapyard-John](#): > > Sounds to me like the issue is going to be with the headers (leaking) or with the tune not accounting for the headers. +1 I had P0420 plus some confusing A/F sensor related code (forgot exact code) raised when I had a quite small leak between the header and the cat. it was not enough to make the ticking sound, but was enough to throw P0420 after 150-300 miles, then get it off and on again randomly [Previous page](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859.md?page=1) [Next page](https://community.cartalk.com/t/what-causes-catalytic-converter-to-fail/178859.md?page=3)