Catalytic Convertor Failure - BMW Luxury Touring Community
 
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post #1 of 8 Old May 11th, 2014, 4:09 am Thread Starter
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Question Catalytic Convertor Failure

Hi has anyone experienced Cat failure yet? My 99 1200LT with 140,000 miles under her belt started making a heavy clonk from low down when accelerating/decelerating!!!! Traced the noise to the first expansion box (the cat)something was very loose inside. Removed exhaust and proceeded to cut open the box to discover the cat had separated from the pipework and was banging up and down the internal pipe. Now here's the problem do I spend £2000 on a new exhaust? I am considering removing the offending cat and welding up the box leaving the oxy sensor in place, figuring that it will still function correctly and not upset the engine management!! Anyone have any thoughts what the long term implications are running without the cat? No worries in UK/Spain re exhaust emission checks (at the moment). Any thoughts re performance and mpg....will they improve? Cheers!
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post #2 of 8 Old May 11th, 2014, 7:50 am
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Re: Catalytic Convertor Failure

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Originally Posted by Tinks View Post
. I am considering removing the offending cat and welding up the box leaving the oxy sensor in place, figuring that it will still function correctly and not upset the engine management!! Anyone have any thoughts what the long term implications are running without the cat? No worries in UK/Spain re exhaust emission checks (at the moment). Any thoughts re performance and mpg....will they improve? Cheers!
Cut it open remove the cat and weld it back up.

Even if you had emission testing, removing the cat would have no effect.
They may however do a visual check for one. (if your bike came with one from the factory)

the dense honeycomb cat is VERY restrictive.

I gutted the cat on my pickup truck and gained 5 mpg.

One thing though.... on the LT, if you gut the cat.... you basically turn that section into a resonator.... which MAY or MAY NOT effect your exhaust tone.

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post #3 of 8 Old May 11th, 2014, 10:45 am
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Re: Catalytic Convertor Failure

I second gut the cat. Mine went bad at about 150k. I removed it and it flows better but sounds pretty cool too. It seems to run better. I havent noticed any excessive emmisions smell either.

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post #4 of 8 Old May 12th, 2014, 1:48 am
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Re: Catalytic Convertor Failure

I have rodded out cats for my track students when the brick broke loose and partially (almost totally) plugged the pipe. As long as you leave the oxygen sensor working and don't mind the tone change you'll likely not detect any difference.

However, do not believe the junk about cats being hugely restrictive. In good shape, they're not. Generally rodding out a cat won't do anything useful for power and when someone calms a substantial benefit it may well be that that vehicle has other more fundamental problems that have gone unaddressed.
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post #5 of 8 Old May 12th, 2014, 2:02 am
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Re: Catalytic Convertor Failure

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Originally Posted by racer7 View Post
I have rodded out cats for my track students when the brick broke loose and partially (almost totally) plugged the pipe. As long as you leave the oxygen sensor working and don't mind the tone change you'll likely not detect any difference.

However, do not believe the junk about cats being hugely restrictive. In good shape, they're not. Generally rodding out a cat won't do anything useful for power and when someone calms a substantial benefit it may well be that that vehicle has other more fundamental problems that have gone unaddressed.
Plus 1. LT's generally run BETTER with fully functioning cats. The motronics are programmed for them.

At 140K it is not unusual for them to be toast. They have a design life - like all things - and that ain't too shabby.

My advice for the OP: Quite screwing around, man up and buy a new one. OR - if you have the skills to take one apart and weld it back together - go out and buy a new section for next to nothing and repair it properly.

I had one of these welded on to my 1987 454 Chevy 1 ton crew cab dually exhaust (that ran like horse hockey) when the OEM cat was toast at 220K. I suck at tig welding, so some things are better left to guys that do it every day for a living and have all the fittings and hangers next to them. It took some custom cutting and fitting. It passed emissions and ran SO much better it was hard to believe. I'm not sure if any of these will fit the LT's exhaust, but they are worth a look. Especially for $3,000 USD for a new one? I would find it hard to invest in something that was the same value as the bike's re-sale value. On a good day. In the spring.

I say: Keep 'em hummin' for $100.00. You've still got 100K miles to go on the engine. Really.

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Last edited by RonKMiller; May 12th, 2014 at 2:55 am.
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post #6 of 8 Old May 12th, 2014, 10:50 am Thread Starter
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Re: Catalytic Convertor Failure

Hi All Thanks for your responses. Well as I said I bit the bullet and took the exhaust off and cut open the box. Sure enough the "brick" was loose and sliding up and down the box. It was fairly badly damaged and looked pretty clogged! Re-welded the box back together (MIG weld) re-fitted the system and went for a ride. As everyone suggested the exhaust note has altered, deeper tone. The performance does seem to be slightly improved, not just on acceleration but also accelerating in higher gear (ie 30mph in 5th) the engine pulls really well. Not sure if the MPG has improved, but due to do some longer journeys over the coming weeks. Once again thanks for your advice.
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post #7 of 8 Old May 12th, 2014, 1:04 pm
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Re: Catalytic Convertor Failure

Aside from the fact that a healthy catalyst results in only a miniscule loss (if any) in engine power at full throttle, there seems to be a disconnect between the removal of the catalyst and modern thinking on safety and heath. The "old" gasoline contained lead compounds to prevent detonation, but since it could cause learning difficulties and poison the catalyst, the lead compound was replaced by compounds containing aromatic hydrocarbons such as benzene and toluene. These don't cause learning difficulties and don't poison the catalyst, but unburned aromatic hydrocarbons can cause damage to the human central nervous system and are carcinogenic in various degrees. Also in the products of combustion could be nitrous oxide, the largest contributor nowadays to the depletion of the ozone layer. The modern three-way catalyst takes care of carbon monoxide, a poisonous gas in itself, unburned hydrocarbons and nitrous oxide. Even though the engine will run without the catalyst, the disadvantages appear to outweigh any possible advantage. Let alone that it is illegal to remove the catalyst.

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Last edited by andres; May 12th, 2014 at 1:11 pm.
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post #8 of 8 Old May 12th, 2014, 1:37 pm
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Re: Catalytic Convertor Failure

gasoline has always contained benzene and it can cause leukemia in children including teenagers, very carcinogenic

Gary
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