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03-04-2013, 08:58 AM | #23 |
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You can buy o2 sensor simulators. I can't recall if the rear o2 sensors are heated or not, but if they are you will need something to simulate the heater so that circuit doesn't throw a CEL.. As we all know the rear o2 sensors are there just to make sure the cats are doing their thing, the front o2 sensors are what actually control A/F ratio.
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03-04-2013, 12:04 PM | #24 | |
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On my diagram, the resistor that goes to ground might be misplaced. It may actually need to be bridging the gap between the input and output of the secondary O2 sensor. I'm tired and I'll think more about it later.
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03-04-2013, 12:41 PM | #25 |
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Correct me if I'm wrong, but since there's effectively nowhere to put the rear o2 sensors, the ideal situation would be to remove them all together? Otherwise you just have them dangling somewhere... On the euro headers there's only the spots for the front o2 sensors.
I see what you're doing though, basically you're using a resistor to modify the input voltage to get to a corresponding output voltage... I'm not terribly familiar with how these particular o2 sensors work, but the ones I'm familiar with operate in terms of duty cycle. I don't think you can do that and get good results, because the o2 sensor still needs to see that proper heating cycle and needs to see the temperature inside the exhaust stream. I think your idea would work if you wanted to install those sensors on the euro headers, but that kind of defeats the purpose here. I wonder if you could somehow piggy back the front o2 sensors and use your method to basically step down the voltage and send that to the rear sensor harness.. The ECM doesn't look for a certain voltage, it expects the voltage to fluctuate with the front o2 sensors.. I believe that the front and rear o2 sensors are essentially the same sensor (except with maybe a longer harness).. Since we're not eliminating the cats, seems fair to me to try and do some trickery, and would seem you could make some sort of little "sorcery box" that you could plug in the factory connections.
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03-04-2013, 12:51 PM | #26 |
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So are you saying the duty cycle is what changes when AFR changes, and not the amplitude?
I could easily program a microcontroller to modify the duty cycle, but it would have to be based off of the primary O2 sensor. All I would need to do would be to splice a wire from primary O2 output and set it to an input on the microcontroller. From there the microcontroller could analyze the signal and output the appropriate duty cycle. The microcontroller's output signal would replace the output signal from the secondary O2 sensor, and it would be fed into the ECU. I guess I could do the same with an analog output if the signal is voltage-based and not based on duty cycle. I need to dig into how O2 sensors work. How can they alter the duty cycle with changes in the AFR? I would think it would need some kind of processor onboard, and I don't think they have them.
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03-04-2013, 12:52 PM | #27 |
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Here's a couple threads on the M3 boards, for your reading pleasure.
http://www.m3forum.net/m3forum/showt...p?p=1064685378 http://www.m3forum.net/m3forum/showthread.php?t=390397 http://mkiv.com/techarticles/oxygen_...tor/index.html http://www.m3forum.net/m3forum/showthread.php?t=337969
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03-04-2013, 12:53 PM | #28 |
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Thanks! I'll check them out and see what I can come up with.
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03-04-2013, 01:03 PM | #29 | |
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I know back in OBDI land, the duty cycle is what the ECU to control the AFR.. Basically it was like an ON/OFF switch, so if it was OFF it would read lean, and if it was ON it would read rich. Depending on how often the sensor switched from lean to rich would change the AFR. Again, this was on OBDI cars where the max the o2 sensor could change the AFR was maybe 10-20%, where I think on more modern cars (OBDII) it can vary it much more. I'm not very familiar with electronics, so please excuse my ignorance if I use the wrong terminology... I think you're right, the ECU looks for the changes in amplitude not duty cycle.. http://www.mr2.com/TEXT/O2_Sensor.html http://en.wikipedia.org/wiki/Oxygen_sensor Bottom line it sounds like your methodology sounds correct. Since a catalytic converter essentially removes the same amount of pollution regardless of how lean or rich it is (not exactly true, but true enough for this discussion), it would seem to me the voltage drop (either positive or negative) would be fairly linear.
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03-04-2013, 01:15 PM | #30 |
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The older OBDI cars were narrowband sensors, and the newer (but not all) OBDII cars use widebands. A narrowband sensor can only tell you if you're lean or rich, whereas a wideband can tell you by how much.
I'm definitely not one to fret over terminology . I appreciate the education!
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03-04-2013, 02:00 PM | #31 |
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Good luck getting a sim to work. We ≠ M3
The rear O2's shouldn't ever be 'dangling somewhere'. They should be placed in the same location as our European neighbors to avoid issues. Cutting, coding for, removing, sims etc... is asking for a CEL and other issues. |
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03-04-2013, 02:07 PM | #32 |
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IIRC O-cha had some experimental simms & I dont think they proved to be completely successful on our cars.
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03-04-2013, 02:33 PM | #33 | |
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Ocha's sims didn't pan out IIRC. And those who have spliced wires to extend the secondary O2 wiring have run into issues as well. The ECU is very picky. I'm not sure if anyone has got a tuner to turn off the secondary, and if so, in doing so left the car "ready" from an OBDII perspective. Like Intg8r said, our ECU isn't the same as the E46 M3, so we can't assume an M3 solution will work (ask those who have tried to tune this car for turbo or supercharger--it's totally different). After I found the parts I was looking for I stopped looking, so beyond the modified section 2 and real Euro cat I'm afraid I'm not a great resource. |
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03-04-2013, 03:08 PM | #34 | |
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I believe evolve has a tune that turns down the rear o2s but still reports ready for smog purposes. This would be the cheapest route with no relocation required. So far though I don't think anyone has posted showing that they did this successfully.
Donovan does have some cats for sale right now, and those things are like unicorns. I'd encourage anyone to pick those up for a proven solution. Oh and somehow I missed this question, sorry Finnegan! Quote:
The reduction in radiant heat for these types of thick ceramic coatings is massive. The direct contact heat is at least 30% lower, which means radiant heat goes down 35-55. Way better than the thin "paint" coatings most people go for.
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03-04-2013, 09:14 PM | #35 |
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Some more info I found about the E46 323ci; whether or not our cars are similar is TBD:
The primary O2 sensors don't have a frequency or duty cycle, and their output oscillates in amplitude from 0.9 volts (rich) to 0.1 volts (lean). The secondary O2 sensors are much more stable. I don't understand this right now, because I would think they would read lean and oscillate with the primary O2 sensors... I guess the cats dampen the oscillation. According to what I read, the secondary O2 sensors don't necessarily follow the primary O2 sensors. So, if my circuit was to work, it would have to have a voltage supply independent of the primary O2 sensors, or simply reduce the voltage of the actual secondary O2 sensor readings. I don't know if the ECU expects an oscillation, or if a constant ___ volts will do the trick (doubt it, because if it was that easy someone would have done it by now). O2 sensors PRODUCE the output voltage. They only work when they get up to operating temp. Prior to this, the car is in a rich "safe" open-loop mode. Once the O2 sensors warm up, they produce the voltage... it isn't supplied to them. The only thing supplied is for the heating element. At this point I believe the 4 wires are heater hot, heater ground, O2 output, and O2 ground. Solution: I could EASILY program a microcontroller to output a signal between two values (0.5-0.7 volts?). The issue is knowing if there's a relationship between the primary and secondary O2 sensor readings, or how the ECU determines if the sensors are actually working. Does there need to be some oscillation? How often? I don't know. If it isn't picky, I could have it randomly oscillate at a slow, smooth rate. The next step will be to get an OBDII tool with data logging capability, and measure/graph each sensor's output simultaneously. Example attached (I claim no rights to the picture).
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03-05-2013, 05:47 AM | #36 |
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I was reading a little what the E90 guys do, and they use a thing called a BMS simulator, and apparently it is adjustable so you can tweak it. Even if our ECU isn't similar to the E46's, it has to be similar to some other BMW so chances are there's a solution out there that will work, we just have to find it...
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04-19-2013, 12:57 AM | #37 | |
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