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2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement #5429599 05/15/20 05:23 AM
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Hi P0420/P0430 code has been on my Lexus LS400 for last 40000 miles or so-has 203000 on it now. Needed a left wheel bearing and asked mechanic about the code and he said would replace right gasket to see if would clear code. On write up after job the mechanic wrote “replaced right CAT gasket hoping to close gap in pipe unfortunately this did not solve the problem therefore recommend replacing just front catalytic converter since that is the flange that’s is bad estimated cost $502.00.

I have owned the car for less than two years-bought it at 134000 miles and it has been whisper quiet throughout. When got the car back yesterday-It sounded louder-much louder like there was a hole in the muffler or I was a teenager who put on an aftermarket exhaust. I went back to place and the mechanic was on the middle of something and the front like phone/scheduling person said-“ohh that is normal for the car to be louder after that replacement. The drivability and acceleration seems fine-and drove about 150 miles to and from work and drive some last night-was checking brakes they replaced and overall stability of the car. Again drives fine but is now obnoxiously loud-I probably would have loved this 30 years ago because it has a cool burbling sound-but am near 50 and it really is loud and noticeable when accelerating at any speed.

I am going to head up there this afternoon after work and talk directly to the mechanic. Is this potentially normal? What could have maybe broken off doing this particular job? My understanding of mechanical stuff is poor-but try to understand as much as can when asking questions. Would be interested in any input and ideas about having a whisper quiet Dr. Jeckyl car to now this thunderous loud Hyde. Thank you

Last edited by spiderbypass; 05/15/20 05:31 AM. Reason: added CAT in front of gasket

Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429606 05/15/20 06:00 AM
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Astro14 Offline
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If the gasket was replaced properly, then the exhaust would be sealed up and quiet.

Two possibilities: one, job was done badly, or two, it wasn’t that gasket.


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429609 05/15/20 06:15 AM
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If the gasket was replaced properly, then the exhaust would be sealed up and quiet.

Two possibilities: one, job was done badly, or two, it wasn’t that gasket.

First thank you so much for responding... likely going there this morning.. I understand the first point that wasn’t sealed correctly as possibility... with your other point-When you say it wasn’t that gasket... could you expand further when get the chance...thank you again

Last edited by spiderbypass; 05/15/20 06:18 AM.

Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429614 05/15/20 06:24 AM
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It sounds like there is a hole in the muffler, because there IS a hole. Your car was whisper quiet when new. If everything was intact and properly installed, it would remain so.

Manifold, down pipe, cat, muffler, I can’t tell where your leak is over the Internet, but you’ve got an exhaust leak, that’s why it sounds like you’ve got an exhaust leak.

It’s a 20 year old car. Lots of things could’ve rusted out.

Or your mechanic is a hack that couldn’t get the system to seat properly.

The moron on the phone that said that it’s typical for a car to be louder after this replacement is utterly wrong. The whole point of this repair is to make the car quieter by repairing the leak.

Your mechanic has failed to do that.


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429632 05/15/20 06:55 AM
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That is just it... even with a leak or problems with the catalytic converter-the car has run impeccably and been whisper quiet-it just became noisy yesterday after the work was done. I am up here now at Mechanics and will update after speaking with him when he gets in about 830.


Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429637 05/15/20 07:04 AM
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Just saw them they said well yes it because there was so much rust buildup when they changed it the sealant they put in there wouldn’t actually seal it back and that’s why they need to take the next step and try to fix the catalytic converter I didn’t have time to argue with them. It is just frustrating I should’ve just let sleeping dogs lie

Last edited by spiderbypass; 05/15/20 07:06 AM.

Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429647 05/15/20 07:15 AM
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Don't replace the Cat with an aftermarket one. If you think the Lexus is now loud(er) with the gasket change, you won't believe how much more sound will come in the cabin with an aftermarket Cat. I changed the Cat's in our Lexus RX with aftermarket ones and I ended up getting rid of the RX. OE Cats are ridiculous in price but, worth it.


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429658 05/15/20 07:29 AM
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Holes in the exhaust are easy to find. If stuff has rusted away leaving a hole of course it needs to be replaced, and usually the metal around the hole is rusted to practically nothing, making repair impractical.

Without leaks to the outside the cat still often affects the noise of the car. Though the primary purpose isn't noise suppression, if the active material inside the cat has fallen out or been removed you will get more noise along with the P0420 code.

Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429679 05/15/20 08:12 AM
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I dont know how this Lexus is built - but usually there is a ball and socket with no gasket - or a fully welded system past the second cat- especially with OBDII - I owned many Fords that leaked like a sieve from the factory - OBD II made them get their "stuff" together.

I remember Toyota on the Original LS400 touting the fully stainless lifetime exhaust system design. Impressive.

I would run away from this moron mechanic. You don't use sealant on an exhaust. At least I never have.

This is teenager clueless shade tree mickymouse.


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429711 05/15/20 08:40 AM
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I felt hopeful that found good place two weeks ago-guy who sold me the car mentioned this place Weikles in Felton Pa and said they work mostly on Toyota’s. They did timing belt and water pump for under 700 and were cool about using Redline D4 for transmission fluid drain and fill... they got me hooked with that and when asked about other services they seemed pricier relatively speaking to timing belt deal.

They were a little tricky too with catalytic converter-they quoted replacement a little over 2000 last week then lady Christina said yes the today I got you a better price it will be 505.00 for converter but only had two year warrranty. Last night started reading up more on Lexus LS400 and I think they have four of them so her deal was simply taking one forth of initial estimate which when read small print was all four of them.

I feel like I am back in 1995 when had my 1988 Chevy Caprice Police package that had louder exhaust storming down the road.


Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429829 05/15/20 11:41 AM
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Find a proper exhaust shop or even body shop that have the ability to weld.


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5429940 05/15/20 02:09 PM
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I'd suggest taking it over to Run Run Exhaust over in New Holland (Lancaster County) and have them look at it. They are an old school exhaust place and have all the proper equipment (tubing, welders, etc) and knowledge to fix exhaust leaks. And they are very reasonably priced!

Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5430250 05/15/20 08:59 PM
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JMJNet
Find a proper exhaust shop or even body shop that have the ability to weld.

VacaI'd suggest taking it over to Run Run Exhaust over in New Holland (Lancaster County) and have them look at it. They are an old school exhaust place and have all the proper equipment (tubing, welders, etc) and knowledge to fix exhaust leaks. And they are very reasonably priced

Thank you very much-really appreciate suggestions and feedback. I have kept contact with the guy who sold me this car for 4000 nearly two years ago-he texted me back with similar suggestion- here is message with his permission

“Weikles is great with troubling shooting & diagnostics- technical things. They are great with Toyota’s & the experience they have working on them is unmeasurable! But items such as exhaust suspension, brakes- basic things- they are no better than most. I’ve found good exhaust work is very hard to find. Not to many good welders or benders anymore. Everyone wants to replace the entire exhaust. The guy in Windsor is backwoods! That’s what you want from an exhaust guy. The 2 times I used him I was very impressed.”
It seems like exhaust work is a niche’ in auto mechanics where you have to have a lot more welding skills and org a creative flair. Thank you again


Insecurity with overcompensation are the root of evil deeds.
Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5430315 05/15/20 11:00 PM
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They probably snapped some studs off trying to remove the up-pipe/catalyst? Japanese exhaust nuts require heat down here in the south much less in the rust belt!


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Re: 2000 Lexus ls400 oud rumble exhaust after right gasket at cat replacement [Re: spiderbypass] #5432962 05/19/20 02:22 AM
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Another question-would a mechanic immediately know before removing and replacing the catalytic gasket cover that it would be problematic to put a new one on because of the rust buildup-or he would not know that until taken off? Again had engine light on for awhile and car drive whisper quiet-now unbearably loud-what should le should not be the responsibility of the shop? They wanted to make appointment to just keep going forth with more work like replacing the CAT-my inspection isn’t until November and wouldn’t even think of that if they replaced the gasket and car was same as before with the light still on. Before going back up there-I want to know if request for them to “fix” gasket for the noise. This sounds like unique situation in that the gasket was almost like a causality of war in terms of diagnosing and fixing the emissions problem.


Insecurity with overcompensation are the root of evil deeds.
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