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FYI/Thorley Header-O2 Sensor

2801 Views 18 Replies 9 Participants Last post by  KesekiSupra
When I first got my car, I used a Bosch O2 sensor, and it passed emissions . I recently failed emissions, and broke down and bought a factory sensor $98. Between tests I had put on a Thorley header. Comparing both O2 sensors side by side, I see why I failed. The Bosch is so short at the tip, that it wasn't even in the exhaust stream. The Toyota sensor is much longer at the tip, and was designed to work with the header, that was, at the time an OEM accessory part. This was an expensive mistake trying to save a few bucks. Live and learn.
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The Toyota one I have doesn't stick out very much on my Thorley, maybe a 1/8 or so. The bosche replacement must be really short, the Toyota one isn't very long either. I thought this might have been one reason I wasn't passing smog but I ran about the same #s on the stock manifold w/same O2 sensor.
What exactly are you failing emissions on? If the 02 sensor is out of the stream or just not working you should have skyhigh HCs and COs. For what its worth I've ran my car with the header and with the stock manifold on the car nearly back to back. The emissions were only slightly better with the stock manifold in place. For the most part the header seems to be a non-issue for me on smog checks.
I doubt the 02 sensor is your problem with NOx levels that high. Are your CO #s really high? They should be really low like 0-.2 ppm. If they are high I'd suspect the converter (like 1ppm or more). When all 3 are high is general a sign of an ailing converter. Even if you have a new high flow converter I'd suspect it. I swapped my new Magnaflow in place of my orginal Toyota cat and all of the #s double or tripled. The only aftermarket cats I've been able to smog on is a brand new Catco. Even after a 2k miles or so even those won't pass. Generally high NOx is the result of hot combustion (i.e it runs lean). When the 02 is MIA the engine should run very rich (high HC and CO). On mine the NOx is high everything else is near 0. You can unplug the O2 sensor and run it and it fail HC,CO and passes NOx near 0. NOx numbers in the high 2000s are way off the scale. I would do a functinonal check on the EGR as well. Those NOx # are extremely high the worse I've done is like 1800-1900 with the EGR unhooked (this is on a 6M on top of my 1100-1200 usual #s)
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