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Discussion Starter · #1 ·
I feel like an idiot asking this but here goes....<p>I'm poking around on fcp groton looking for oxygen sensors because I believe I have narrowed my problem down to those. I find 2 of them, one before the cat and one after.<p>So I put the car up in the air and I start from the back.<p>Muffler.... ok good ..... a resonator... ok good ..... the cat (or so I thought) and then oxygen sensor #1, flexpipe, oxygen sensor # 2.<p>What the hell? Are there 2 resonators besides the muffler, and the cat is somehow hidden up in that tiny little flexpipe?<p>On my E46 the cats are in the manifold, I did not expect to find something equally whacked out on this car.....
 

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Re: Umm.... Is the cat in the flex pipe ? (CoconutPete)

</i>"What the hell? Are there 2 resonators besides the muffler, and the cat is somehow hidden up in that tiny little flexpipe?"</i><p>No.<p><IMG SRC="http://i614.photobucket.com/albums/tt222/plainv70/swedespeed/Untitled-1.jpg" BORDER="0"><p>The three-way catalytic converter (TWC) stores oxygen found in the exhaust gases and uses it to make toxic gases more environmentally friendly. The catalytic converter is a 3–way catalytic converter in which HC (hydrocarbons) and CO (carbon monoxide) are oxidized and NOx (nitrous oxide) is reduced. As the three-way catalytic converter (TWC) ages, its ability to store oxygen is reduced. The conversion capacity of the three-way catalytic converter (TWC) is reduced and unburned residue which is harmful to environment is released. To reduce the environmentally damaging emissions, the engine control module (ECM) checks the efficiency of the three-way catalytic converter (TWC). In brief, this check is carried out as follows.<br>Two heated oxygen sensors (HO2S) are used to check the three-way catalytic converter (TWC) one upstream and one downstream of the catalytic converter. The main function of the heated oxygen sensors (HO2S) is to measure the oxygen content in the exhaust gases so that the engine control module (ECM) can maintain the fuel–/air mixture at around λ=1. This mixture provides optimum three-way catalytic converter (TWC) efficiency. To determine catalytic converter efficiency the amplitude of the heated oxygen sensor (HO2S) signals is compared (amplitude is a measure of signal oscillation).<br>When three-way catalytic converter (TWC) efficiency is good and the fuel–/ air mixture is normal, the front heated oxygen sensor (HO2S) signal switches between rich and lean while the rear heated oxygen sensor (HO2S) signal is even. When three-way catalytic converter (TWC) efficiency is poor and the fuel–/ air mixture is normal, the rear heated oxygen sensor (HO2S) signal switches between rich and lean because the exhaust gases are passing straight through the three-way catalytic converter (TWC) without being converted.<br>If the amplitude of the rear sensor becomes too great in relation to the amplitude of the front sensor for a number of checks, a diagnostic trouble code (DTC) will be stored for catalytic converter efficiency.<br><BR><BR>
<i>Modified by MrTippy at 2:02 PM 7-10-2009</i>
 

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Re: Umm.... Is the cat in the flex pipe ? (MrTippy)

Ok. Part # 1 on that diagram appears to be the cat... which would be right in line with what I saw.<p>The part that threw me off was that one part was listed as "oxygen sensor before cat" and one was listed as "oxygen sensor after cat" I guess I Just misunderstood and they are in fact both "before" the cat but one is "upstream" and one is "downstream".<p>I guess I'll just order both of them and hope for the best!
 

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Re: Umm.... Is the cat in the flex pipe ? (CoconutPete)

Per VADIS:"Two heated oxygen sensors (HO2S) are used to check the three-way catalytic converter (TWC) one upstream and one downstream of the catalytic converter. "<p>I could not find a better picture in VADIS showing their location.<p>They would not be of much use if they were both on the same side of the cat.
 

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Discussion Starter · #5 ·
Re: Umm.... Is the cat in the flex pipe ? (MrTippy)

Ok. Part # 1 on that diagram appears to be the cat... which would be right in line with what I saw.<p>The part that threw me off was that one part was listed as "oxygen sensor before cat" and one was listed as "oxygen sensor after cat" I guess I Just misunderstood and they are in fact both "before" the cat but one is "upstream" and one is "downstream".<p>I guess I'll just order both of them and hope for the best!
 

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Re: Umm.... Is the cat in the flex pipe ? (CoconutPete)

Have you had the dtc read? if the sensor(s) is(are) bad, there will be an error code. Are the two sensors the same? (I thought so.) If, so what are the odds that both went south at the same time? Do you need to buy two?
 

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I just finished replacing my front HO2S after a diagnosis from the stealership that it was bad. After I finished the job and turn over the motor, it's running even worse than before, surges at idle and quickly stalls out. Anyone know something I don't? It seemed like a simple plug/unplug job. I bought a brandy-new HO2S from myswedishparts.com, who I've used before and never had any issues with...
 

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Re: (arls116)

Could be an ETM, do you have the original? There is an extended warranty on them, ask your dealer.<p>Also, re o2 sensors, get your codes read again, see if there is anything still there. Any parts shop can do it for you.<p>And listen to oceans60r he knows what he is talking about.
 
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