Has anybody seen what are the electronic characteristics of the post cat O2 sens signal?
07-07-2004, 08:36 PM
#1
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Has anybody seen what are the electronic characteristics of the post cat O2 sens signal?
PEB tunnas, have you devised a post cat signal generator?
I logged hours of block 031 to see what was the signal like in everyday driving and I think that it might be pretty easy to reproduce from the pre cat O2 signal. What Ive seen is that the signal is fairly constant (small AC component) but sort of follows the pre cat signal at a lower voltage (maybe half the voltage). Im thinking an AC dec follower opamp circuit with a variable voltage divider on the output will do. Then a properly heat dissipated resistor to mimmic the O2 sensor itself. This way we can do away with the whole wiring and sensor.
Any thoughts?
I logged hours of block 031 to see what was the signal like in everyday driving and I think that it might be pretty easy to reproduce from the pre cat O2 signal. What Ive seen is that the signal is fairly constant (small AC component) but sort of follows the pre cat signal at a lower voltage (maybe half the voltage). Im thinking an AC dec follower opamp circuit with a variable voltage divider on the output will do. Then a properly heat dissipated resistor to mimmic the O2 sensor itself. This way we can do away with the whole wiring and sensor.
Any thoughts?
07-08-2004, 03:55 AM
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Sounds like you are on to something... i can't offer much help but please let me know how it works..
sounds like you are preposing to tap into the circutry of the primarys to benchmark the "signal" that the ECU sees from the secondarys.
from what I have read. the trick is to have an acceptable delta between the primary and secondary O2 signals so the ECU won't protest and throw codes.
I am not PEB certified but those are my thoughts
from what I have read. the trick is to have an acceptable delta between the primary and secondary O2 signals so the ECU won't protest and throw codes.
I am not PEB certified but those are my thoughts
07-08-2004, 05:46 AM
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According to Todd@AWE, the S4 doesn't use the secondary O2 sensors for mixture control at all...
This is contradictory to what the Bentley manual says...
<img src="http://d.pramanik.home.comcast.net/post/o2s.GIF">
... but I tend to believe Todd over the Bentley in this case. APR has no issues with ignoring the secondary sensors with its testpipe programming.
-Dave Pramanik
<img src="http://d.pramanik.home.comcast.net/post/o2s.GIF">
... but I tend to believe Todd over the Bentley in this case. APR has no issues with ignoring the secondary sensors with its testpipe programming.
-Dave Pramanik
07-08-2004, 06:19 AM
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nice work. now who has a scope and a dyno? hell you could prolly get good enough signal trace...
just sitting in the garage reving...
this post-cat O2 sensor-emulator would be nice!
this post-cat O2 sensor-emulator would be nice!
07-08-2004, 09:14 AM
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A couple thoughts.
I'm am not familiar with the term 'AC dec follower', but I think you want to use a DC amp for the O2 sensor signal. As far as I know, the DC component of the signal is what the control stuff looks at.
I saw somewhere (here, I think) that someone just used the forward voltage drop of a diode to reduce the pre-cat sensor voltage to a lower value. Personally, I'd give that a try first - seems like that would be a lot simpler than wiring up op amps.
I agree with you that a power resistor could be used to simulate the heater element in the O2 sensor. I assume that is one thing the ECU checks to see if everything is ok. It might be worth checking to see if you can get away without it. You could measure the resistance of the heater wires on the sensor to see what value to use. I'd be tempted to try higher resistance values to reduce the amount of heat that is generated. It could be the ECU is just making a rough check of current flow and you could get away with a lot less.
hope that helps,
Dave
I saw somewhere (here, I think) that someone just used the forward voltage drop of a diode to reduce the pre-cat sensor voltage to a lower value. Personally, I'd give that a try first - seems like that would be a lot simpler than wiring up op amps.
I agree with you that a power resistor could be used to simulate the heater element in the O2 sensor. I assume that is one thing the ECU checks to see if everything is ok. It might be worth checking to see if you can get away without it. You could measure the resistance of the heater wires on the sensor to see what value to use. I'd be tempted to try higher resistance values to reduce the amount of heat that is generated. It could be the ECU is just making a rough check of current flow and you could get away with a lot less.
hope that helps,
Dave
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07-08-2004, 10:23 AM
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don't think thats contradictory at all
sounds like the stock programming does, but testpipe software can be made to ignore it.
what i dont get is why you can't write software to totally ignore the post cat o2's and not throw dtcs in the first place... unless thats in a different part of the ecu?
what i dont get is why you can't write software to totally ignore the post cat o2's and not throw dtcs in the first place... unless thats in a different part of the ecu?
07-08-2004, 10:30 AM
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No, what Todd said is that the stock code makes no reference to the secondary O2 sensors...
with regards to mixture control. That's exactly the opposite of what the Bentley manual says.
Oh and APR's 2+/testpipe programming does exactly that... throws away the DTCs from the secondary O2 sensors. There's no need to ignore the data from the sensors since they don't affect mixture control.
-Dave Pramanik
Oh and APR's 2+/testpipe programming does exactly that... throws away the DTCs from the secondary O2 sensors. There's no need to ignore the data from the sensors since they don't affect mixture control.
-Dave Pramanik