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Old 10-22-2009, 09:13 PM   #11
calvin1234
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Quote:
Originally Posted by 03OrangeSVT View Post
FOR THE LAST TIME THE SECOND O2 HAS NOTHING TO DO WITH IT GOING INTO OPEN LOOP!!!!

The Second O2 sensors ONLY job is to determine the efficentcy of the CAT NOTHING ELSE.
Read Ford's "OBD System Operation Summary for Gasoline Engines" it says it does more:
Quote:
As the front UEGO [wide range o2 sensor] sensor ages and gets exposed to contaminants, it can develop a rich or lean bias in its transfer
function. The rear bias control (also called FAOSC Fore/Aft Oxygen Sensor Control) system is designed to
compensate for any of these bias shifts (offsets) using the downstream HO2S sensor. The "FAOS" monitor looks
for any bias shifts at the stoichiometric point of the front UEGO sensor lambda curve. If the UEGO has developed a
bias beyond the point for which it can be compensated for, lean (P2096, P2098) or rich (P2097, P2099) fault codes
will be set.
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Old 10-22-2009, 10:29 PM   #12
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Yes it sets fault codes but is NOT the determing factor for the engine going open loop from the rear o2 being unplugged

Everyones a tuner these days

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Old 10-23-2009, 01:43 AM   #13
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Quote:
Originally Posted by 1turbofocus View Post
Yes it sets fault codes but is NOT the determing factor for the engine going open loop from the rear o2 being unplugged

Everyones a tuner these days

Tom
OK, I'm confused... then please explain this quote from the same manual
Quote:
Due to the fact that intrusively driving the CMS sensor rich will cause drivability and emission concerns, there are
other several condition counters that have to fail prior to intrusively forcing the sensor to go rich...
If it does nothing except check the cat how can it cause drivability concerns especially when earlier the same manual said most failures of the cat were because the cat was exhausted and not plugged?

I may not be a tuner but I have a 2 year degree in computers and electronics and work on a 2 million dollar machine for a living that is much more complicated than any Focus you or I will ever work on, so you will understand my natural curiosity in everything about my car.
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Old 10-23-2009, 09:40 AM   #14
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The rear o2 can measure heat and add fuel (very rare), once the fault is set the ECU no longer is able to use the rear o2 and no longer looks at it and relies on the front o2 sensor as long as the front o2 is working properly it will keep the engine in the proper fueling

Your quote says it self "there are
other several condition counters that have to fail prior to intrusively forcing the sensor to go rich... " To go rich not to go open loop and the top quote also says nothing about going open loop but driving it under a rich condition will cause driveability issues again nothing about it going open loop

The rear o2 has the ability if in place and working to add fuel to cool the CAT as thats is the job of the rear o2 , If it is not there it sets the code and the ECU does nothing as it has no information and does not set the ECU to open loop like the front failing can do


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Old 10-23-2009, 09:53 AM   #15
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Thank you for clearing that up for me.
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Old 10-23-2009, 10:02 AM   #16
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Well, it looks like, regardless of it going 'Open Loop' or not, the system can go rich from rear O2 failure?? Which makes this argument somewhat pointless...doesn't it?

He's clearly having a rich condition, as evident from his mileage. If the only change he made was disconnect the rear O2 (I think the ECU can probably compensate for the highflow cat difference), then my suspicions tell me it's the rear O2 causing this...

If not the O2 by itself, which Tom says, then the combination of the rear O2 and something else causing the issues...
I'd replace the front O2 regardless at this point, and see what happens.
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Old 10-23-2009, 11:02 AM   #17
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From the way I understand it, and Tom, clear this up for me if I'm wrong, the rear o2 will set a code if it detects a rich/lean condition, and then pretty much throws the data from that sensor to the wayside after the code is thrown.

However, the portion of the quote from whatever manual that came from that explains the bias compensations seems to be taking place. The car seems to go rich once (or twice) per drive cylce, and then clear up. This makes me think that the system is indeed attempting to remedy something, then realizing it can't fix the problem, and then goes back to whatever it was running off of before, as the misfire/rich condition completely disappears and everything goes back to normal.

The other option is that the front o2 is just wonky, and is causing everything.
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Old 10-23-2009, 11:29 AM   #18
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Quote:
Originally Posted by WuNgUnSVT View Post
Well, it looks like, regardless of it going 'Open Loop' or not, the system can go rich from rear O2 failure??
No if the rear sensor fails it will not cause the system to go rich, the only changes the rear O2 can make (and they are very small changes) are to help control the temp of the catalyst... trying to keep it in the optimum operating range.

If the sensor fails all you're going to do is get a code letting you know it failed and nothing more.

In the tune there are no tables for the rear O2, only an on and off switch. Weather you are running rich or lean is soley controlled by the front O2 sensor.
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Old 10-23-2009, 11:31 AM   #19
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The rear o2 only changes fuel if the cat temps are high if cat temps are not high then no fuel changes are done , if that was the case then turning off the rear o2 would mean changes in the fueling would need to be addressed

The front o2 , tps , timing and a few other things controles the MPG , Me I would log the front o2 and see what it is reading as well as TPS and load anything more then doing that is all speculation

100`s of Foci owners before him have unhooked/mil elim the rear o2 and never had this issue

Tom
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Old 10-23-2009, 12:13 PM   #20
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Well, the next time I get home, I'll grab my Xcal and do some logging.
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