Removed one cat, car sounds like garbage. Will removing the other fix it?

[indy525]

My car threw the CEL and soon after had a rattle coming from the exhaust. Debated on whether to replace the cats or just remove them. EVERY good review on all universal cats had at least one bad one to go with it. Didn't feel like wasting money on a universal cat that was bound to fail early.

Found a shop that would hallow out the cats and weld them back on. Driver's side was the culprit, he said the passenger one was ok and to leave it on. I debated, but decided to leave one cat and could have the other removed later. I figured I'll just add non-foulers to get rid of the code.

Now, exhaust tone sounds like crap. I understand that because only one of the cats is removed the exhaust tone is dominated by one cylinder bank. Exhaust is raspy. I'm looking for a nice deep v8 rumble without drone. So here are my options:

1. remove the other cat (if it fixes the exhaust tone, this would be my #1 option)

2. Replace with universal cats

3. Replace cats with universal resonators

again I want my exhaust to have a deep rumble, right now it sounds raspy. I'm open to removing/replacing scuba tanks and or/ resonator in the near future.

Thought on what to do next?

[wagons ho]

When removing cats, it's best to replace it with a piece of straight pipe. The open volume of the cat shell builds turbulence and hurts flow.
And removing a cat should have no effect on sound, unless the other side is clogged also.

[edjack]

What about smog inspections?

[indy525]

Lucky to have no smog inspections in Indiana

- - - Updated - - -

When removing cats, it's best to replace it with a piece of straight pipe. The open volume of the cat shell builds turbulence and hurts flow.
And removing a cat should have no effect on sound, unless the other side is clogged also.

I've read that removing cats has no effect on sound and have read the opposite. In my case it made a difference. My theory is that I'm really only highlighting 4 of the 8 cylinders, hence the crappy sound.

[edjack]

If you don't mind polluting the environment, remove the other cat.

However, check with your DMV. You may need to show that the smog stuff is intact when selling.

[dannydoo]

Performance wise,you just moved the torque levels to different areas and gained a couple horses at best. Lost something holllowing it out too. Cant remember, look around youll see. Hollow out the other one. But it sounds like you need a diff muffler. Theres tons of u tube videos on these. GL Post a video,I wanna hear it.

[geargrinder]

With a few exceptions, the only reason to put "piggies" (aka 'hogged out' cats) back on is to pass visual inspection while having cat deleted. Mostly I think cat delete is stupid - the HP difference is negligible and mythological in many if not most cases, and indeed it stinks and pollutes more, but, when it becomes economically ridiculous to jump through hoops for a car with declining market value, then I have no issue with it and would agree with Wagons, put straight pipes in unless you need the piggy there to pass a visual. Of course unless you get your tune tweaked, the DME is going to throw codes and a CEL, and if the car ever goes to a state w/ an OBD scan inspection it'll be hosed, but again, if that works for you, fine.

Removing cats on most cars absolutely does impact the sound as the cats are calculated into the muffling equation of the system. Especially on a non-turbo car. The only time it might not woudl be a car that is "over muffled" to begin with. Probably pulling a cat off a Toyota Camry or Honda Accord wouldn't make much difference, these cars are not like that.

Despite the teenage fanboiz claims to the opposite, I don't think fully demufflered M6x motors sound that great, I think they sound a bit raw and 'cheap loud', but most 'louder is always better' types don't have much discerning taste for tone, and so I'm not surprised at what you have found here. I think these cars sound best with some kind of good muffler system, as opposed to 'deletes', and the cat delete might be running you into that scenario. I've not heard a 1/2 catted V8, but... OK maybe I can imagine what you're saying that maybe there's a weird 'crappy resonance' thing occurring, but it also just might be the "muffler deleted M6x motors don't sound as good as losers with poor taste think they do".

[edjack]

I have Magnaflow cats on mine, and the exhaust is somewhat edgier than with the original cats, esp at idle.

Note that the BMW cats also have a built-in "silencer."

[indy525]

I'm kinda concerned to why they failed in the first place. Whenever I talked to someone about replacing the cats they all say, "well they shouldn't be failing..." especially after they find out the car only has 61k miles. It does seem like there are a higher rate of failure for e39s. So maybe I'm not that concerned. Car ran super strong and quiet before all this crap happened.

I do agree with you geargrinder that the m62 is not the best sounding engine uncorked. I'm sure it sounds worse because 4 cylinders are choked and the others aren't.

Gotta figure out what to do...

[geargrinder]

higher rate of failure for e39s.

Higher than what? As a rule bmw oem cats are really good and I would have said the opposite. Not a hugely common thing - not unheard of but not high frequency really.

[XAlt]

Isn't the pre-TU cat setup a little less restrictive than ours?

[geargrinder]

Yeah, but its because the NV doesn't have "pre-cats" in the manifolds. So its more about the manifolds than the "real cats" which are the same I believe. Those "pre-cats" supposedly impact startup only when the main cats are cold and not working yet, and are there to accommodate newer emissions standards. So the pre-TU manifolds are a mild performance improvement, and if you look at them you can see obviously how much better they are than the nasty TU "catifolds". While I'm not a huge believer in de-catting power gains, this is a different story - pre-cat setups are usually pretty bad because they constrain the exhaust manifold significantly.

[indy525]

Higher than what? As a rule bmw oem cats are really good and I would have said the opposite. Not a hugely common thing - not unheard of but not high frequency really.

My highly scientific compilation of past threads created about this. There does seem to be quite a bit of activity on the subject dating all the way back to 2003 or so.

[geargrinder]

Thats a load of poop I say. Just because people mention it / have threads doesnt mean its a high frequency quality issue. Cats are a PITA and expensive and if somebody does have a problem, unlike some other 'normal' stuff, they are far more likely to go searching around for answers like "can I do without them" and "is there a cheaper than OEM option". Cats are not particularly poor or a frequent issue on these cars. Other things, sure. Cooling systems, some bushings, some gaskets, etc. etc. Not the cats. As I said, doesn't mean one won't go bad here and there, but they aren't a notable weakness vs. any other normal car, and in fact the cats themselves are probably better than a lot of cars. I know a shi7ton of guys w/ E39's and E38's, many pretty high miles cars. Hard pressed to remember anybody having a real cat failure issue although I'm sure somebody I know has.

[philly98540]

IIRC some of the early E39's (not sure about E38's) had a history of premature cat failures. They would start to rattle. The dealer replaced them under warranty. This was waaaaaay back. Mine were replaced, that is how I remember this. The old original ones were obround in cross section. The dealer replaced them with round ones. In any event, the BMW cats, in general, are some of the best. They are very long lived if the the car is kept in tune. They carry a huge price tag and command top dollar in the scrap yards due to the high precious metal content.

[JimLev]

I know a shi7ton of guys w/ E39's and E38's, many pretty high miles cars. Hard pressed to remember anybody having a real cat failure issue although I'm sure somebody I know has.

Ummm a shi7ton of guys. Guess I'm one of them, LOL.
153K and 17+ yrs old, main CAT on pass side coded 2 weeks ago for efficiency.
I'm sort of surprised it didn't last a bit longer.
Haven't done anything about it yet, no emission testing or inspection are done here.
Will probably buy 2 new ones so I don't have to do the job twice.
Guess it will either be HJS, Magnaflow, or ???, still looking at what's available and will require the least amount of work to replace them.

[XAlt]

E38 M62NV cars tend to be the ones that eat cats. Typical post goes like this.

>"hey guys I'm misfiring on bank 1 and I've put thousands into the car"
<"It's the cats"
>"but they tested just fine"
<"just do it"
>"wow thx guys problem solved"

[geargrinder]

Ummm a shi7ton of guys. Guess I'm one of them, LOL.
153K and 17+ yrs old, main CAT on pass side coded 2 weeks ago for efficiency.
I'm sort of surprised it didn't last a bit longer.
Haven't done anything about it yet, no emission testing or inspection are done here.
Will probably buy 2 new ones so I don't have to do the job twice.
Guess it will either be HJS, Magnaflow, or ???, still looking at what's available and will require the least amount of work to replace them.

Ha ha - bummer Jim. But still - close to 20yrs on the cats - that's not too bad.

I've heard such mixed things about the Magnaflows, don't know what to make of them... from double thumbs up to double thumbs down... I had a short list of cats on my list back when I was hotter for re-doing my exhaust... if I find it I'll shoot it over.

E38 M62NV cars tend to be the ones that eat cats. Typical post goes like this.

>"hey guys I'm misfiring on bank 1 and I've put thousands into the car"
<"It's the cats"
>"but they tested just fine"
<"just do it"
>"wow thx guys problem solved"

Sounds like those are the same NV ones Philly is talking about.

[JimLev]

I'm not really bummed out it failed, knew it wouldn't last forever. This is the longest I've ever owned the same car.
Back in the good old Roadfly days some of the guys had good success using DEC CAT's.
http://www.deccats.com/catalog_page.php

I don't see any prices listed, will need to call them up on Monday.

[indy525]

I'm not really bummed out it failed, knew it wouldn't last forever. This is the longest I've ever owned the same car.
Back in the good old Roadfly days some of the guys had good success using DEC CAT's.
http://www.deccats.com/catalog_page.php

I don't see any prices listed, will need to call them up on Monday.

Bavauto sells DEC. They seem very reasonably priced for direct fit replacements.

[JimLev]

Bavauto sells DEC. They seem very reasonably priced for direct fit replacements.

Thanks for the info, didn't know they sold them. When we lived in MA I would go to BavAuto at least once a year for the Show and Shine.

[topaz540i]

Cat life has alot to do with engine health. Run rich forever and dont bother fix the problem and you will clog them right up.
jim (prob on his way to go see the new Fast and Furious movie as we speak :0 ) runs nos which probably burns insanely hot (hotter than car is designed for) and probably shortened the life somewhat. Alot of drivers baby their car never going over 3k rpms which could contribute to clogging as well as they never fully burn off from all the lugging. I suspect that jim driving like an old granny wore them out.

[geargrinder]

To summarize - Jim shortened life by both be more abusive, and, not abusive enough, to his car. I agree.

Srsly I do like this theory and think it prob has merit. People like to think that DME adaptation is the perfect cure all to everything but IME it is not. For example failing/failed CCV systems dumping extra oil into the intake are going to be real hard on the cats.

Cat life has alot to do with engine health. Run rich forever and dont bother fix the problem and you will clog them right up.

[JimLev]

To summarize - Jim shortened life by both be more abusive, and, not abusive enough, to his car. I agree.

Ha! The car is never babied.
I've only used the juice once last August so it isn't from that.
The DEC cat's from BavAuto are still pretty expensive, about the same as the HJS cat's that Philly and BMW540san are using.

[indy525]

Ha! The car is never babied.
I've only used the juice once last August so it isn't from that.
The DEC cat's from BavAuto are still pretty expensive, about the same as the HJS cat's that Philly and BMW540san are using.

Hey Jim, do you have a link for more info on the hjs cats?