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7 Series - E38 (1995 - 2001)

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  #1  
Old 02-23-2014, 01:50 PM
R3DNA R3DNA is offline
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catalytic converter replacement 97 740i

I'm replacing the catalytic converters on my 97 740i and I'm wondering if there's anything I need to look out for, or any tips on making it easy. Any help or info is greatly appreciated.
It looks pretty straight forward, already have both pipes, but have not gotten underneath the car yet to see how difficult the removal and installation will be.

Thanks
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  #2  
Old 02-24-2014, 05:25 PM
jmorgenson jmorgenson is offline
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Unless your exhaust is already modified, those catalytic converters aren't bolted on, they're welded.
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  #3  
Old 02-24-2014, 06:57 PM
R3DNA R3DNA is offline
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I guess it's been modified because the CC's I have just need to be bolted on. I'll take a photo and show you what I've got.
I spoke to a BMW certified mechanic and he said it should be fairly easy.
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  #4  
Old 02-24-2014, 07:46 PM
CitizenOfDreams CitizenOfDreams is offline
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Quote:
Originally Posted by jmorgenson View Post
Unless your exhaust is already modified, those catalytic converters aren't bolted on, they're welded.
I don't think you can find too many E38s with the original welded cats still in service. Replacement cats were attached with clamps, even when serviced by a BMW dealer.

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  #5  
Old 02-24-2014, 09:16 PM
R3DNA R3DNA is offline
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This is great! Thanks for posting this. The cats on here look exactly like the ones I have. I'll figure out the O2 sensors, bracketry etc.
As shown in the diagram, #3 the gaskets, will I need to have replacements, or can I re-use the ones already there? I believe they're metal.
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  #6  
Old 02-24-2014, 09:38 PM
CitizenOfDreams CitizenOfDreams is offline
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Quote:
Originally Posted by R3DNA View Post
As shown in the diagram, #3 the gaskets, will I need to have replacements, or can I re-use the ones already there? I believe they're metal.
Sometimes you can reuse them, sometimes they are too far gone. No way to tell until you take the flanges off. So better have them ready before you take the car apart.

The gaskets are not metal, they are made from some graphite mix. They can break and chip.
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  #7  
Old 02-24-2014, 09:44 PM
CitizenOfDreams CitizenOfDreams is offline
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P. S. I suggest you also buy a complete set of nuts and bolts for the exhaust flanges. You may have to break some of them off, especially if the previous owner replaced the proper copper nuts with regular steel ones. Ask me how I know.

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  #8  
Old 02-24-2014, 09:49 PM
CitizenOfDreams CitizenOfDreams is offline
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P. P. S. Try not to break the outer flange bolts (as in the picture above). They are a [female dog] to get out. I tried hammering out the broken one, but it would not budge. I spent an hour hollowing it out with a Dremel and a carbide end mill. Only then it gave up.
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  #9  
Old 03-11-2014, 05:51 PM
R3DNA R3DNA is offline
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I installed the new CC's and it wasn't that difficult. I'll need to tighten them after the car runs a few times to seal the connection completely. I was wondering if there's a sealant I should use to make it as quiet as possible?
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  #10  
Old 03-20-2014, 11:48 PM
tomloans tomloans is offline
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Where is the least expensive place to buy new cats...?
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  #11  
Old 04-07-2014, 07:34 AM
dave38 dave38 is offline
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Have a 97 E38 that needs new cats(that's what the dealer says is causing the periodic loud thumps under the floor) and wondered what brand you used for replacement and any problems with fitting to existing pipes.

Here in MA, my 1997 is exempt from emissions testing and I could even eliminate the cats, but don't want constant CEL warnings. Any further info on your experience and photos is appreciated.
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  #12  
Old 04-07-2014, 07:50 AM
CitizenOfDreams CitizenOfDreams is offline
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Quote:
Originally Posted by dave38 View Post
Have a 97 E38 that needs new cats(that's what the dealer says is causing the periodic loud thumps under the floor)
Catalytic converters causing loud thumps? Are you sure it's not your driveshaft center bearing?
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  #13  
Old 04-07-2014, 08:34 AM
dave38 dave38 is offline
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The thumps are random several minutes apart, sometimes never happen on a short trip.
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  #14  
Old 04-07-2014, 08:44 AM
First740i First740i is offline
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I had small thump in my cats also. The inside can comes loose. If you don't have to worry about emissions gut them out and your car sounds/runs better!!

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  #15  
Old 04-07-2014, 01:06 PM
dave38 dave38 is offline
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Thanks for the response. I assume one must cut the pipe nearest to the cat and extricate the guts. If so is there a pipe sleeve available to rejoin and clamp?
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  #16  
Old 04-07-2014, 01:30 PM
First740i First740i is offline
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There should be a flange holding the exhaust pipe to the cat. Unbolt the flange, pull the pipe away. Get a long bigger screwdriver and pound that **** out ( you will see a comb like thing in there). Now you can keep what you pound out and scrap it not worth much, but money is money!!

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  #17  
Old 05-08-2014, 08:46 AM
dave38 dave38 is offline
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Cats gone!

Had an independent shop remove the cats guts yesterday (very reasonable), and vehicle runs great. No misfires or CEL's yet. Thanks for the tip. Anyone with misfire problems and not subject to emissions testing should give this a try.
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  #18  
Old 05-08-2014, 09:37 AM
First740i First740i is offline
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Nice. Glad i could help!

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  #19  
Old 05-08-2014, 04:12 PM
R3DNA R3DNA is offline
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Not sure if this is related or not, but after replacing my cats every now and then the car almost stalls out. The CEL comes on about every 4 or 5 trips, and then goes out on it's own. It reads that it's a mass air flow sensor. I will replace my air flow unit, but I was wondering if anyone has had the same issue after replacing their cats. It feels as though it completely gets the air shut off and the car wants to stall out, only happens for a second, then accelerates fine after that.
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  #20  
Old 05-15-2014, 06:24 AM
Dans 750 Dans 750 is offline
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The o2 has to heat up to 600 something degrees if it doesn't it tells the computer to dump more fuel in the engine in order to heat it it up to that temp. The mass airflow tells the engine how much air and the temp of the air coming into the engine in order to tell the computer how much fuel to put out. So really the two are kinda related. You could test the temp of the cat while it's running and hot with a laser temp hand held tool there pretty cheap. Measure the temp before the cat and after the cat I believe there should be 100 degree difference between the two. Also check for those fricking vacuum leaks that can cause those kinda issues.


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  #21  
Old 07-25-2014, 10:53 AM
Yemdogbuc Yemdogbuc is offline
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Hello, I'm new on here so please be patient. I have a 2001 740 il sport. Check engine light is on, the code reads cylinder 1 and 2 misfire. I've changed all the plugs and coils still misfire. I've checked the fuel rails mas sensor, no change. I'm guessing the cc are bad. They aren't rattling. Do I need to change all 4?


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  #22  
Old 07-25-2014, 11:02 AM
tomloans tomloans is offline
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how does it run? Any changes to performance? Don't start changing out anything until you diagnose. How many miles on the engine... Give us the exact code number and verbiage please. Also clear the codes and then let us know at what RPM does the misfire occur that is if you are able to notice it?

Have you changed out the cam Sensors yet? don't do it, I am just asking...

Crank Postion Sensor (CPS) - controls when the plugs fire
Cam Postion Sensor (CMP) - controls when fuel is injected. fuel injection
Note: These two are tied together so it all happens at the right time
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  #23  
Old 07-25-2014, 11:46 AM
Yemdogbuc Yemdogbuc is offline
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The car runs ok, but after 40mph the power decreases. You can also here the car grumble when accelerating. It's as if the exhaust has a leak or something. The car also shakes a little at stop lights. When you step on the gas, the rpm goes up, the the speedometer stays put. I took the car to an indy. First he said the secondary air pump. Then he claims the intake hose. Now he's telling me that the rings have locked up. HOW? The engine only has 127890 on it.


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  #24  
Old 07-25-2014, 11:52 AM
tomloans tomloans is offline
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You need somebody who knows this car. Where are you located?
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  #25  
Old 07-25-2014, 11:54 AM
Yemdogbuc Yemdogbuc is offline
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I'm in Upper Marlboro MD


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