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Discussion Starter #1
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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I noticed that too. The bosche's body is also shorter. This may be handy for those that are limited in space. I can't fit the toyota o2 due to where I mounted the o2 bung on my half custom header, only the bosche fits. But it is deep enough for my header.
 

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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.
 

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this is kinda OT, but ive really noticed that spending a little more on toyota parts can really pay off in a longer haul.
 

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you know what you may be right, I have some DT headers too and I bought a new Bosch O2 sensor and it didnt want to pass smog. I guess Ill be getting that toyota O2 sensor.

BTW is there some kind of part number to get for that Toyota O2 sensor?
 

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Discussion Starter #6
I went through the diagnostic today, and again it's bad news. I failed emissions again, but the numbers are much better. It seems that the O2 sensor is working, but it is only registering from 4/10 of a volt to a 6/10 of a volt variance, and doing that slowly. If you rev the engine, it spikes the one volt change it is capable of, so the theory is that it works but is not in the exhaust stream enough to make the necessary voltage changes. I'm going to measure the stock manifold, and then call Thorley, and see what they say. The mechanic was also concerned that possibly the ceramic coating on the header was not letting the sensor ground properly, but we were unable to get the proper changes by clipping a ground on the sensor body. I'll let you know what I find out. Back when these headers were OEM, emissions were not run on a dyno, so maybe they never really worked very well.
 

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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.
 

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Discussion Starter #8
HC failed the 25MPH test 249ppm, limit 118ppm. NO failed both the 15 and 25MPH test. 2656ppm at 15MPH limit 937ppm. 2977ppm at 25MPH limit 853ppm. The sensor on the stock manifold is at least 3/4" into the exhaust flow, and less than 1/4" on the header if that.
 

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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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Discussion Starter #10
CO is .01 and .12 for both tests respectively. You are most likely right about the CAT, but temp readings indicated it was working. They weren't sure if it could do it's job because of the lazy operation of the O2 sensor (only fluctuates between 2 and 6 tenths of a volt, and slowly at that). Tech at Thorley agrees that the position of the sensor in the header is not in the exhaust stream enough for it to work right. I will most likely relocate the sensor to the collector, so the sensor can monitor O2 on all six cylinders instead of only 1, 2, and 3 and position it so it is in the pipe as deep as it is in the stock manifold. EGR is working. The valve and modulator is less than a year old, I cleaned the blocked passages in the plenum ( the lower pipe is clean), the BVSV is spot on, and the VSV vacuum switch has been replaced. The readings I gave you were before the timing was corrected, it was at 22 degrees for the test ( please don't ask how that happened), so the numbers were much lower when it was corrected, but still too high to pass.
 

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Discussion Starter #11
Pulled the header off today and had the O2 sensor flange welded directly to the pipe. The sensor was not in the exhaust flow at all with the Thorley setup, so even using the longer Toyota part, there is no way that it could have ever worked properly. Had to weld studs to the flange with this setup, but it just makes installing the sensor that much easier. I'll let you know how it runs with a working O2 sensor in the header. The Cat. looked good, so I'm hoping it will go through emissions this time. There was not enough room to relocate the sensor to the collector.
 

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Discussion Starter #12
Put everything back together this morning, and this car has never run better. It has much more power, especially at the top end, and it easily pulls 7,000RPM before the power flattens out. This is a must do modification of the Thorley header. From the face of the flange to the inside of the pipe shouldn't be much over 5/16". This thing rocks now, it unlocks the true potential of the header.
 

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GreyFalcon

How did the O2 sensor relocation work at the emissions test?

Also, does the O2 voltage change faster and with a bigger swing now?

What you've described makes a lot of sense, but before i start welding on my header I'd like to hear how the smog tests went.

Dale
 

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Discussion Starter #14
It passed emissions, but my cat. was also gone and the motor is a little tired with 197,000 miles on it, so NOx was still a little high. It won't pass in two years from now when they drop the numbers again. The biggest benefit was the power increase. It is a different motor altogether. Most noticeable is drive-ability, low end power and it will run itself into the rev limiter in a heartbeat now. I got a good 7,000RPM out of it once before I posted, and then the limiter started kicking in every time, at just under 7,000 RPM. I had a marginal automatic transmission that is being changed now. It was real fun for a couple of days. With cleaned and balanced injectors, I believe this car could be a little beast. If you have a ceramic coated header, find a way to ground the O2 sensor directly. I bolted a large braided ground strap to one of the sensor's studs, and then attached the ground wire to that so it wouldn't burn up, but there may be a better way.
 

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might try cleaning our your egr if it doesn't pass next year. high nox numbers are usually because of a clogged/not working egr valve
 

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Discussion Starter #17
All my systems are clean and working, hoses, belts, including timing have been replaced, EGR passages cleaned, valve and modulator replaced, VSV replaced and all other components test correctly. Valve seals and guides are a bit of a problem, and I could very well have injector problems, that I haven't gotten around to checking yet. There could be a bad connection in a connector somewhere for all I know. I failed emissions, with the new cat (just barely), so Toyota replaced the new O2 sensor I had just purchased. It passed the next time. I was somewhat near the limit on NOx on the 25MPH test, so if I don't find anything else wrong, I'll either rebuild or put in a rebuilt 6M before the next test.
 

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Discussion Starter #18
I'll try to get pictures when I go under to replace the transmission.
 

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any suggestions to go about cleaning the EGR and stuff? i really need help with this. My car hasnt passed smog and i have like 1 week until my free re-test is void. my cat is pretty much dead so i bought a new one (im sure that shuld help) I failed on the NOx. but this is my total reading ill scan it. btw it says the test weight on the car was 3.3k LBS. arent these cars supposed to only weigh like 2.4k? jeez. oh yea, and i also bought a cooler running thermostat tho my car was never overheating, it was always just a nudge under half way. SO maybe it is a dirty EGR? any suggestions? id really like help on cleaning the EGR or watever please =\ thanks

 
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