Car has 2 catalytic converters. If I remove one...

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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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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).
 
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.
 
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.
 
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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
 
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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.
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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.
 
Originally Posted By: Klutch9
W 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.

You're considering breaking federal and/or state laws to gain 5 whole HP?
 
One of them may be a "pre-cat," placed close to the engine to light off sooner. It's mostly there for cold start emission control, and the second cat actually does most of the "work."
 
Originally Posted By: Hokiefyd
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.

That may be - but why even consider it? Cats are designed to last the lifetime of a vehicle. I've seen vehicles go 200K - 300K or more on the original cat and still pass smog, this is of course assuming that the vehicle was properly cared for. My Aerostar has the original cat with over 200K miles.

Not to mention - sometimes "theoretical questions" aren't as "theoretical" as they might seem!
 
There should still be a difference int front and rear O2 readings.
That should satisfy the computer monitor.

Will it throw a code? Who knows ? There are too many individual parameters here.
Some guys are lucky - they have actually removed the cat with no codes being thrown.
 
Originally Posted By: Hokiefyd
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.


This.

Also, could a Mod please lock this thread? Some posters are turning it into an argument/accusation fest, and it's going nowhere.

For those of you who input useful, constructive information, I appreciate it as always.
 
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