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#2575597 - 03/21/12 11:23 PM Car has 2 catalytic converters. If I remove one...
Klutch9 Offline


Registered: 01/07/09
Posts: 2237
Loc: Rochester, MI, US, World
Will I get a CEL? This is for down the road, should one of them fail. My Focus is a PZEV so it has 2 catalytic converters. AFAIK, the second o2 sensor (post cats) just measures a change in temperature. So if one cat was still there, I think the sensor would still be happy. Also, I think the PZEV model makes 5 less hp because of that 2nd cat; I know they're quite restrictive. I might even pick up an mpg or two.
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#2575609 - 03/21/12 11:28 PM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
motor_oil_madman Online   content


Registered: 11/29/09
Posts: 2354
Loc: Houston, Texas
If their is an 02 sensor after the second cat then I bet it would throw a CEL.
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#2575613 - 03/21/12 11:31 PM Re: Car has 2 catalytic converters. If I remove one... [Re: motor_oil_madman]
Klutch9 Offline


Registered: 01/07/09
Posts: 2237
Loc: Rochester, MI, US, World
Originally Posted By: motor_oil_madman
If their is an 02 sensor after the second cat then I bet it would throw a CEL.


There is, but that one cat will still reduce EGT's, which is what the second o2 sensor is usually looking for.
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#2575614 - 03/21/12 11:32 PM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
Chris142 Offline


Registered: 06/05/03
Posts: 13729
Loc: apple valley, ca
Yes it will throw a CEL. Usually removing a cat decreases power and economy since the computer is designed with both cats in and working.
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#2575641 - 03/21/12 11:55 PM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
stephen9666 Offline


Registered: 12/08/06
Posts: 3140
Loc: USA
Originally Posted By: Klutch9
AFAIK, the second o2 sensor (post cats) just measures a change in temperature.


This is a little confusing to me.

If the "second o2 sensor" only measured temperature, then it would be a temp sensor, not an oxygen sensor.

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#2575650 - 03/22/12 12:04 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
tommygunn Offline


Registered: 01/27/11
Posts: 3061
Loc: usa
Secondary sensors measure O2 after the cat and compare it to the upstream. The way cats work there should be a different amount of oxygen in contrast to the upstream, as the reaction causes O2 to go up (or down, I can't remember the exact reaction...but it should be different at any rate).

If O2 levels are the same before and after the cat its reasonable to assume the cat is no longer functioning and the CEL goes off.

So, is there still a cat between your upstream and downstream? Good. It could be fine if thats still the case. But obviously if you change it who knows what it could do.

Obviously if its a straight pipe between upstream and downstream eventually it'll complain.

It does nothing to measure temperature.
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#2575654 - 03/22/12 12:05 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
rpn453 Offline


Registered: 11/06/02
Posts: 4842
Loc: Saskatchewan
The oxygen sensor measures oxygen. It's not looking for temperature changes, it's looking for a smoothing of the oxygen readings. That's why a spark plug anti-fouler can often compensate for converter removal. By removing the sensor from the direct stream, the changes it sees occur less rapidly.

This would probably be vehicle-dependent. Check a more specific forum to see if anyone has experimented with this on a similar Focus.
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#2575693 - 03/22/12 12:58 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
pzev Offline


Registered: 11/30/05
Posts: 601
Loc: arctic
Might have been changed for O7, but on the earlier Focus Duratecs, there was only 02 sensors on the upstream "mani-cat" (exhaust manifold/catalytic converter combination). The second did not have any accompanying 02 sensors, which means you can remove it without worry of a CELL.

However, they could have changed that in later model years. The bottom line is this...if there are 02 sensors after the second catalytic converter, then yes, you'll throw a CELL if you remove it.

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#2575696 - 03/22/12 01:05 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
strongt Offline


Registered: 03/01/07
Posts: 371
Loc: So. Utah
I'm betting if you remove the 2nd Cat you'll trip the CEL. Besides why remove it? I'm sure Ford put some pretty low restriction Cat's on that model. It would make them look bad on the green side for selling a PZEV clean air car that get worse MPG's for being a "Green" model.

Shoot my Jeeps got 3 Cat's. 2 Pre-Cats by the engine and a Cat after those.
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#2575731 - 03/22/12 05:08 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
NHGUY Offline


Registered: 10/09/11
Posts: 4576
Loc: USA
They added the 2nd sensor to check up on the cat.With OBDII it has to sense and report any condition that may cause excess emissions.But I really bet they added it after all those years of people hollowing out the cats to appear legit but in actuality do nothing at all.People cant do that anymore (and thats a good thing for emissions overall).

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#2575802 - 03/22/12 07:42 AM Re: Car has 2 catalytic converters. If I remove one... [Re: rpn453]
dwcopple Offline


Registered: 10/11/04
Posts: 3582
Loc: Michigan
Originally Posted By: rpn453
That's why a spark plug anti-fouler can often compensate for converter removal. By removing the sensor from the direct stream, the changes it sees occur less rapidly.

This. buy 'em at Advance Auto and remove the cat.
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#2575866 - 03/22/12 09:06 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
lexus114 Offline


Registered: 05/12/08
Posts: 6113
Loc: Easton, PA
Dont mess with the emissions system. Your car isnt going to run that much better anyway, if at all. You might pick up a little low end, but the top end will suffer. Today`s Catalytic Converters are not nearly as restrictive as they used to be. I remember my Mom`s 77 Pontiac Gran Prix, when you would floor it, all you would hear was air from the exhaust. It had that pancake style converter on it, and they always seemed to clog up.


Edited by lexus114 (03/22/12 09:09 AM)
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#2575886 - 03/22/12 09:28 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
JTK Offline


Registered: 08/14/03
Posts: 8545
Loc: Buffalo, NY
What are you trying to gain by removing one of the CCs?. It's a Focus and it's relatively new being a 2007 w/ only 38Kmi? You're not going to get a noticeable performance or economy gain.

You've got years and miles left on your Federal emissions warranty coverage anyway. If something should happen to the remaining CC w/in the 7/70 Fed warranty and they see you hacked the exhaust, your SOL.

Joel


Edited by JTK (03/22/12 09:30 AM)
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#2575987 - 03/22/12 10:58 AM Re: Car has 2 catalytic converters. If I remove one... [Re: lexus114]
jeepman3071 Online   content


Registered: 04/15/10
Posts: 2249
Loc: Storrs, Connecticut
Originally Posted By: lexus114
Dont mess with the emissions system. Your car isnt going to run that much better anyway, if at all. You might pick up a little low end, but the top end will suffer. Today`s Catalytic Converters are not nearly as restrictive as they used to be. I remember my Mom`s 77 Pontiac Gran Prix, when you would floor it, all you would hear was air from the exhaust. It had that pancake style converter on it, and they always seemed to clog up.


This. Plus it is against federal law. I'm surprised your post is still here, as most online forums prohibit the discussion of removing cats and emission equipment. hornets
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#2575993 - 03/22/12 11:01 AM Re: Car has 2 catalytic converters. If I remove one... [Re: Klutch9]
Hokiefyd Offline


Registered: 06/24/04
Posts: 13736
Loc: North Carolina
Guys...re-read his first post. He's simply asking a theoretical question should one of his converters eventually fail 100k miles down the road. He never said he has plans to remove it.
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2009 Honda Ridgeline RTL
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