Air/fuel ratio and Downpipe anit-fouler mod assumption + question (long)
03-15-2006, 01:30 PM
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Air/fuel ratio and Downpipe anit-fouler mod assumption + question (long)
Hi all,
Please correct me if my assumption is wrong / incomplete:
A lot of after market downpipe has their 2nd O2 sensor BEFORE the cat (e.g. APR, Labree), hence the primary sensor and secondary sensor's reading is almost the same, and that triggers the CEL for Cat below efficiency code.
The anti-fouler mod was intended to move the 2nd O2 sensor away from the downpipe so that it will read less O2 and that would trick the ECU that there is a working Cat exists between the primary sensor and secondary sensor, and thus no CEL.
However, since the reading from the 2nd O2 sensor does not reflect the real situation, the ECU is not going to be able to feed the right (ideally 14.7?) ratio of air / fuel to the engine (although the ECU is thinking that its doing the right work). So if it runs rich, eventually the Cat will blown. If it runs lean, the timing of ignition will be wrong such that the piston may in some case work against the combustion (i.e. ignition happens when piston is only moving 80% downward). This will eventually bring damage the piston / cam.
Here comes the question:
1) The knock sensor will comes in the play when the above mentioned situation happens, correct?
2) How much retard in timing will knock sensor and what does it based on?
3) So the most correct way is to manually move the 2nd O2 sensor below the cat and forget about the anti-fouler mod at all, correctly?
Sorry for the long post - I try to ask some exhaust guys and he had no idea what I'm talking about....so AWers, please help!
Matthew
Please correct me if my assumption is wrong / incomplete:
A lot of after market downpipe has their 2nd O2 sensor BEFORE the cat (e.g. APR, Labree), hence the primary sensor and secondary sensor's reading is almost the same, and that triggers the CEL for Cat below efficiency code.
The anti-fouler mod was intended to move the 2nd O2 sensor away from the downpipe so that it will read less O2 and that would trick the ECU that there is a working Cat exists between the primary sensor and secondary sensor, and thus no CEL.
However, since the reading from the 2nd O2 sensor does not reflect the real situation, the ECU is not going to be able to feed the right (ideally 14.7?) ratio of air / fuel to the engine (although the ECU is thinking that its doing the right work). So if it runs rich, eventually the Cat will blown. If it runs lean, the timing of ignition will be wrong such that the piston may in some case work against the combustion (i.e. ignition happens when piston is only moving 80% downward). This will eventually bring damage the piston / cam.
Here comes the question:
1) The knock sensor will comes in the play when the above mentioned situation happens, correct?
2) How much retard in timing will knock sensor and what does it based on?
3) So the most correct way is to manually move the 2nd O2 sensor below the cat and forget about the anti-fouler mod at all, correctly?
Sorry for the long post - I try to ask some exhaust guys and he had no idea what I'm talking about....so AWers, please help!
Matthew
03-15-2006, 02:21 PM
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So our 2nd O2 sensor is just...
..being used to see rather our Cat is working or not, right?
And the anti-fouler mod simply move the O2 sensor out of the way so it tricks the ECU thinking that everything is perfect, Right?
And the anti-fouler mod simply move the O2 sensor out of the way so it tricks the ECU thinking that everything is perfect, Right?
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03-15-2006, 05:01 PM
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Hahahaha...yes....^_^
btw..if I move the O2 sensor after the cat, then there is no need for anti-fouler mod, right? I am thinking instead of doing the anti-fouler mod, I should route the sensor behind the Cat instead of the current position (you know APR has theirs before the cat...sucks man).
Matthew
Matthew