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7 Series - E38 (1995 - 2001)

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  #1  
Old 05-21-2013, 05:34 PM
heavymetal2005 heavymetal2005 is offline
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Location: Beaver Creek, MN
 
Join Date: Nov 2012
Posts: 4
Mein Auto: 97 740iL
Catalytic Converter

Hello, this is regarding a 1997 740iL with 215K.

Issue: Both catalytic converters (CEL)

I've replaced:
All plugs (platinum 4) and boots
valve cover gaskets (due to oil in spark plug hole)
both front and rear o2 sensors (there was a CEL for one o2 senor before CAT, but I replaced them all)

I've notice that on hot days I can hear a whining sound coming from under the car right were the CATS are. This usually happens after I drive it for about 15 to 20 minutes. Last winter the CEL flashed when I was accelerating. This was a misfire due to the CATS. Oil and antifreeze seem fine so I'm ruling that out.

What I'm trying to find out is if there is anything else I would consider checking before I replace the CATS. I just don't want to replace them and then have them go bad in a few months because I overlooked something. Your feed back is appreciated thank you.
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  #2  
Old 05-21-2013, 08:04 PM
Mayorchuck Mayorchuck is offline
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Location: Farley, MO
 
Join Date: May 2013
Posts: 707
Mein Auto: '96 740iL
A good muffler shop can check the flow of the cats to see if they are plugged. Did you replace your sensors with Bosch? This car does not like aftermarket sensors and will often cause it to throw codes. I replaced both my cats with Magnaflow 94105's. Amazon sells them for about $70 each with free shipping. Might be able to get most of that back by selling your bad cats if they are originals. Just be out the cost to cut and weld the new ones on.

If they are bad, replace them. The back pressure is not good on your engine. Really nothing you need to do further to prevent hurting the new cats. Some suggest 87 octane gas shortens the life of the cats but I run QT 87. Had mine for 2+ years and counting. JMO
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  #3  
Old 05-22-2013, 05:23 AM
heavymetal2005 heavymetal2005 is offline
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Location: Beaver Creek, MN
 
Join Date: Nov 2012
Posts: 4
Mein Auto: 97 740iL
Yes I used Bosch o2 sensors only. Thanks for the feed back ill go ahead as planned and get those CATS fixed before more problems arise. I only use 89 and up octane, I love my BMW to much to mistreat it with 87 octane. Once again thanks.

Last edited by heavymetal2005; 05-22-2013 at 05:26 AM. Reason: added to post.
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