I'm not sure what you're paying the tech to clear the codes and take a reading but I would think in the long run it would be cheaper to buy a reader and do the clearing and reading yourself unless you just happen to get it right the first time.

The reader would also probably be nice to have for other things in the future, for clearing future codes and diagnostics.

So far I haven't paid anything for the code reading/clearing. Most shops around my area do it for free. I'll probably offer something if I'm going to be stopping by daily while I fiddle with things trying to get it dialed in.

Today I started in on the trial and error path to clearing these damn codes. The first step was to take the upstream defoulers off. Then I removed the drive's side downstream defouler to compare my options and decide which one to install back into the downstream spot. As I said in a previous post, I have a set of 90degree ones and a set of straight ones. The pictures show one of each. It just so happens that the 90degree ones come apart and it offers me a second set of straight defoulers. As you can see, the removed, straight section of the 90 degree set has a noticeably larger hole and is about 1/8 of an inch shorter. I figured I'd try this options first before I start modifying any of them. You'll also notice the 90 degree set actually has part of it inside the exhaust tube while the straight options are really just spacers. You'll also notice that its depth into the pipe is adjustable because of the nut on the threads. If you want to get that tip you can spin the nut all the way up to the corner, or if you want to back it out, spin the nut down towards the tip. I really wish I could screw the O2 sensor into the corner piece but it dosen't fit. The aformentioned adjustment would really have been nice. But with the extra distance that corner adds, I'm not sure the adjustability will get the O2 sensor close enough to the pipe compared to the straight ones.

I'm not sure how much sense this makes as I try to explain it but I hope it's not total jibberish. As always, I'm open to any and all ideas and suggestions.

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The first post I made on this thread... Why are you still attempting to trick the PCM with defoulers/spacing back the sensor. This is actually retarded if you think about it.. you'll never achieve the proper a/f ratio with your new headers because this sensor is f_cking crucial in spraying the correct amount of fuel in proportion to air. Tricks won't work and the headers might as well not be there. Get the proper a/f tune via piggyback or Dyno shop or just put manifolds back on. Peace ✌️👽

Respectfully disagree.

The crucial sensor is the upstream sensor, this is the one that should not be messed with as it will certainly impact the A/F mixture as previously mentioned by me. The 2 upstream sensor should be left alone.

However, the only purpose of the 2 downstream sensors is to monitor the efficiency of the catalytic converter. By installing headers and getting rid/changing the converter you end throwing codes. The defouler on the downstream sensors could absolutely work to trick the ECU without any negative drawbacks (other than the obvious increase in actual emission output).

Going the route of an actual piggyback/standalone and a dynotune would absolutely be the "correct" way to do this while also gaining some performance, however, this will not fix the issue of the ECU throwing a catalytic code due to it just not being there.

Sorry for missing the question earlier, been tied up with finishing my my rig.

I picked up this OBDii reader on amazon and it has paid for itself 10 times over by now: Amazon.com: FOXWELL NT301 OBD2 Scanner Professional Mechanic OBDII Diagnostic Code Reader Tool for Check Engine Light : Automotive

With regards to my process, it was trial and error. Basically what I was seeing was what you described from your test as well, 0 reading at first, and a significant lag behind the upstream as you got into the throttle.

My initial setup included having a stacked defouler (so a total of 2), this was the first thing I removed. I went down to just a single defouler, plugged everything in and went for a drive to monitor the O2 readings. What I saw was an improvement, but still there was noticeable lag, as well as no reading down low at idle.

At this point basically what I did was modify the defouler a bit more so that I can sit the o2 sensor deeper down into it, I believe I accomplished this by grinding down the top portion of the defouler that the O2 sensor bottoms out on. I did this 2 times before I got the readings to looks some-what correct.

At this point I reset the codes and just started driving... and what do you know, after 2 days all my systems initialized and I no longer had pending codes pop up.

It certainly is a bit of a process.. and I am pretty sure I'll have to re-do this with time as the converter gets even less efficient, but at that point I will be working backwards probably and spacing the sensor back out a bit.


So if my assumptions are correct, there are probably 2 adjustments that you're working on... first and foremost, it is the depth of the o2 sensor to ensure that it sees exhaust flow early on, the second, is the fine-tune of the opening to increase/limit the amount of exhaust gas it sees... not saying that this will work with no cats in place.. but certainly fixed my issues and the logic sounds fairly sound to me..

Yes thanks. I was referring to the upstream a/f sensors not the downstreams.

And here I thought I was going crazy.

I did a set of the shorties and welded the cats on. I triple checked for leaks in my welding and made sure I was good for a seal on the block. I think there is a hole in my muffler that I'll be replacing at the same time. I don't have any emissions checks so I'm just going to get some cats that are the proper length and send it if they are the issue. Maybe I can pay for the new cats with the old ones.

Still seems like I might have a leak on the block so this winter I am going to pull the body and re-check everything. I know the cats were in great condition because I was able to look at them. I might have a set of cats on standby just in case I need new ones.

I've got 4 codes and they're all o2 sensors. Both upstream and downstream are reading off and while I have zero issues going down the road and mileage isn't an issue I've pretty much ignored them for a year.

Would a piggyback tuner help? I haven't done any other mods so tbh while the headers help with flow I don't think a tune is necessary? I only got the headers because the crack was pretty bad and I didn't feel like doing this again in another 150k.



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Yeah the downstreams being off will also throw codes for the upstreams. I went with the resistor/capacitor trick for my downstream dummies, the spacer guessing trick I'm not sure about. Throw a high flow intake on her since she's exhaling much better she needs to inhale much better as well.. then tune that h0e properly. Doug thorley would probably include the tuning technology the same as a superchargers do but the emissions laws won't let them or even talk about it with customers.

Well I guess I'll go ahead with that line. It does make sense in a way.

I made my own sealed high flow for my 3rz in conjunction with a snorkel so it isn't unfamiliar territory. This build wasn't supposed to be the same way though. I got a limited v8 because I wanted to be comfy LOL

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You'll still be comfy but maybe just a little more sucked back into the seat. Vroom.

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I picked up the code reader that you recommended and took a look at the live data. I did notice a difference between bank 1 and bank 2. I think I mentioned it before but what I did is; I made the modifications to the driver's side defouler and left the passenger side as it was. I wanted to see if there was a difference between the two setups. And I did in fact see a difference. So here are my 2 big questions 1. is bank 1 the driver's side and bank 2 the passenger side? 2. Do you have any idea what the numbers should be either at higher RPMs or at idle? Cruising at highway speed I was getting around .895 on bank 1 and .857 on bank 2, and of course, it dropped to zero at idle. Is a difference of 4 hundredths significant?

Sorry for so many questions but this is yet another task that I have to learn myself to get it done right. I'm really disappointed with my mechanic for having nothing for me on this. I guess once you get into aftermarket parts, a lot of shops just want to avoid it. Hopefully I can get these defoulers to work for now while I look further into Jakeepoo's suggestion.

Id like to say bank1 is the drivers side bank.. but last time I was trying to figure this out I believe I ended up being all sorts of confused.. so who knows.. a quick way to tell would be to just unplug a down stream sensor from one side and see which code pops up, bank 1 or 2. It should come up pretty quick with it completely disconnected.

To answer your other question, i do not believe a 4 hundredths is significant at all, no. Not to mention I "think" the Ecu only compares pre and post cat numbers, so the bank 1 - 2 slight differences shouldn't matter.

Again.. this is all just my theory that ended up working out for me.. but if my thinking is that in order to correct the issue for the voltage not showing up at idle you are adjusting the in/out position of the sensor. In your case it needs to be inserted further into the exhaust stream. If the higher rpm cruising number of .857 (unfortunately I don't know what the limits are prior to the ecu throwing a code.. ) ends up being too high, you are then working on modifying the size of the opening for the exhaust to enter. In your case if it high it would need to be closed up slightly.

I haven't had to do this, and can't recall EXACTLY what my numbers were, but I don't think they were far off from the .8xx's. If I had to close up the opening slightly, I think I would look into using small dabs of JB weld to start closing up a bit of the opening a little at a time.



maybe...? lol sounds like you're on the right track.. and I know it can be frustrating.. but if it work it should work pretty decent for a while

Here is the information on the O2 sensor for 5th gen. Yours I imagine work the same, perhaps different values, same principle. This waveform is what to look for. By the way everytime you unplug that you'll have to reinitialize the PCM. You can monitor them from the PCM terminals with a multimeter. You tuned yet?

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