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Old 09-03-2018, 07:42 AM   #1
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I am finally at the stage where I am plugging in the electricals but have a potential problem.
The cats I removed from my 99, 2.5L had 2 O2 sensors, the replacement cats I installed have NO spots o put in the O2 sensors. I think I figured out the forward one by removing the plug on the manifold and putting one set of O2 sensors there, now what do I do with the aft ones?

This is the original cat I removed


This is the replacement cat which also came off a 99 2.5L

Any assistance will be greatly appreciated.

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Old 09-03-2018, 09:38 AM   #2
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Get the correct catalytic converters or have O2 bungs welded onto the set you have.
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Old 09-03-2018, 10:01 AM   #3
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Removed post.
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Old 09-03-2018, 10:39 AM   #4
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There are 2 sets on 97-99 cars for a total of 4 O2 sensors; the 2 pre-cat O2 sensors which are used for fuel ratio and 2 post O2 sensors which monitor catalytic converter health.


Last edited by particlewave; 09-03-2018 at 01:02 PM.
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Old 09-03-2018, 12:30 PM   #5
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I'm not sure where you got this, but it is wrong.
Ok, I'll have to check my info. In the meantime, I removed my post. Thanks.
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Old 09-03-2018, 02:13 PM   #6
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When troubleshooting an O2 issue, I think there was information that ROW early model cars only had 2 O2 sensors.
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Old 09-03-2018, 03:13 PM   #7
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There are 2 sets on 97-99 cars for a total of 4 O2 sensors; the 2 pre-cat O2 sensors which are used for fuel ratio and 2 post O2 sensors which monitor catalytic converter health.

So what your'e say is that CATs I bought were for MY 2000-2004? My only options are to (1) remove and replace Cats with correct ones or (2) have an insert welded to the existing ones so I can install O2 sensors?

The cats I have in now does not have the spot (#4 on the 2000-2004 diagram) to insert an O2 sensor. Do I have some sort of mutant catalytic converter???

Is there any "Hack to bypass the aft O2 sensor? Will the car start and run with the aft O2 sensors not attached to anything?

All I want is for this project to be over with...
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Last edited by flouese; 09-03-2018 at 03:19 PM. Reason: omitted two data points
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Old 09-03-2018, 03:28 PM   #8
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All cats should have position 4/2 bungs (position 4 on 2000-2004, position 2 on 97-99).
As long as you have pre-cat sensors installed, the car will run fine, but you'll get a CEL for failing cats since the DME won't see a signal for the post cat sensors and will think they have failed.

You need the pre-cat sensors for fuel ratio.

I don't know if there are any post cat O2 emulators on the market.

Last edited by particlewave; 09-03-2018 at 03:33 PM.
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Old 09-03-2018, 03:32 PM   #9
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All cats should have position 4/2 bungs (position 4 on 2000-2004, position 2 on 97-99).
As long as you have pre-cat sensors installed, the car will run fine, but you'll get a CEL for failing cats since the DME won't see a signal for the post cat sensors and will think they have failed.

You need the pre-cat sensors for fuel ratio.
Thanks fr the response. I feel better now. Hopefully I can find someone to weld new "bungs" in the existing cats.
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Old 09-03-2018, 04:22 PM   #10
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