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Old 08-28-2012, 11:26 PM   #1
zsoufi1
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cats & o2 sensors and.... mechanic bs?

So my emissions test is coming up in september and I have headers and a straight pipe with a muffler on my car... well thats not going to work so I purchased some used cats, an oem exhaust and o2 sensors from a junk yard. my mechanic said he cant connect the oem exhaust to the cats because the cats I purchased wont fit the exhaust pipes because they are from a different year & model car. So now i am driving around on just the cats until i find a new exhaust... but all the o2 sensors are plugged in and im still getting all the codes for the o2 sensors! should that be happening even if i dont have my exhaust connected to the cats?

btw I erased the codes with a crappy walmart code reader, could that be a reason to why the codes came back on?

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Old 08-29-2012, 06:19 AM   #2
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So now you have your 'exhaust' just ending at the cats? You have all 4 02 sensors?

If you erased the codes and they returned, it's the car, not the code reader...however crappy it is, I'd say.

Did you do the straight pipes yourself? If so, you should have anticipated the emissions test. You know guys use 02 emulators or some such devices to hide emissions problems.

Not much help, I know, OP...sorry about that. Ask in your regional forum...maybe there's a good muffler shop around that could get you fixed up.
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Old 08-29-2012, 08:23 AM   #3
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no that was great help thank you very much. But exactly like you said, the exhaust ends at the cats and im getting all 4 o2 sensor codes as well as the thermostat code. So i thought due to not having any kind of exhaust beside the cats that that may be the cause of the codes but i guess not..

And I'm sorry I bought my e46 about 6 months ago and never was really into customizing unti now so I am new to all this stuff What exactly is a 02 emulator? does it go right where the sensors are supposd to go?
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Old 08-29-2012, 08:33 AM   #4
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When you drive on the highway, is your temp gauge reading a little to the left of dead center? If so, your therm could be stuck open and that would lead to the car running rich, and all your 02 codes.

Read fanatics until you convulse. Start with considering a complete cooling overhaul...but maybe for now, just therm will help you. Get OE--wahler I think is the maker.

...and in the future, sticking to what bmw gave you will ensure you end up with a car at the end that is a bmw. Why would you trust the hacks that the guys here are doing more so than the bmw engineers? Our engineering friends spent hours studying 'stuff' and using volumes of data on results...collected in the many years bmw has been in business.

I'm sorry, but I'd take the accumulated wisdom of bmw engineers over the accumulated wisdom of 'most' fanatics any day of the week.

Be careful. There are many mods you can do obviously, but I'd guess that a good 90% of them aren't quite done right, and that 95% of them come at the price of unwanted, unanticipated consequences.

An emulator is a device built that sends a made up signal to the DME to tell it that the car is running fine...when it might not be. It's a hack; a bypass; a final act of desperation to get a car to pass an emissions test.

I wonder if your car was coded when you lost your cats? I don't really follow this stuff to much, because I've followed it enough to know I'll never be playing around with my car like that!
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Old 08-29-2012, 09:30 AM   #5
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Ya the temp gauge does read a little to the left. I should be able to replace it myself this weekend hopefully

The previous owner said he paid the smog guy under the table to just pass his emissions for him; so I visited the smog guy and he wanted $400 to pass is illegaly and I just said the heck with that... It was too loud and had a disgusting sound, everything was falling off because of the vibration so I went and bought the original exhaust system from a junk yard.

But thanks for the help I really appreciate it. I'll post back if those codes go away after I change the thermostat, that may help someone else whos got the same issue. I searched fanatics 3 hours last night couldnt find a thing so hopefully someone will find this thread helpful
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Old 08-29-2012, 11:15 PM   #6
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I changed my thermostat and my thermostat code went away but all four o2 sensor codes still exist... I took it to a smog guy to reset my computer for me, i drove 200 miles today and I went back to him and the codes still appeared but my catalyst test never completed, neither did the oxygen sensor heater test nor the secondary air system test.

I have also installed back all original cats, all orignial o2 sensors, and original exhaust today. no help at all...
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Old 08-30-2012, 05:22 AM   #7
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Hmmm? You know, I recall of guys being asked if they've plugged the right O2 sensors in in the right place. I'm not up on the specifics of how you could go wrong doing this, but evidently it's possible.

I don't know how the sensors are different besides having different length wires, but you seem to have them plugged in just sitting somewhere it sounds like. They'd need to show some signal...thus the emulator.

This is beyond me, I'm afraid. I think kpeng had a thread on headers...maybe there's something in that thread that will help you.

(I'm assuming you've had all those 02 codes since you removed your cats...is that right?
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Old 08-30-2012, 06:44 AM   #8
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Just an idea, but do you think that since the system is open after the cats, perhaps the reading on the O2 sensors after the cats might be off? I mean its technically seeing more oxygen (outside air) since the system is not closed around that area. IDK, maybe Im crazy.
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Old 08-31-2012, 12:28 PM   #9
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thanks for all the help everyone. Ill look into kpegs post. As or the exhaust having a little open air.. Im actually missing one screw from my exhaust because I lost it.. and theres a tiny bit of air escaping from that area because the exhaust isnt sealed to the cats all the way. I didnt think this would be an issue but Im heading over to the dealership right now and buying that screw. Hopefully that will fix the issue
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