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Old 06-10-2004, 10:09 PM   #1
bigdweeb
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Default No CEL yet!

Having said this, I've probably jinxed myself but here goes anyway.

Since I did a full exhaust a couple months ago I have been living on and off(mostly on) with a CEL. When I did the exhaust I found that the threads on the rear O2 sensor were damaged and wouldn't screw into my new cat. I had no option at the time but to use a Walker wire-in replacement sensor that came with poor wiring directions. I immediately got a CEL with that sensor... It was at one point a PO420 and eventually became a PO136.

I had enough of the CEL and decided to do something about it. I started weighing my options and the electronic MIL eliminator didn't seem like the best option due to the emission testing in my area. I read a bunch about the mechanical fix and tried it out. I bought the Help! P/N: 42002 and drilled one out to .5". This didn't get rid of the PO420 code. I gave it one more shot... this time with a new oxygen sensor.

I bought a new plug-in Denso O2 sensor from oxygensensors.com (P/N: 234-4706) and took another look at my Help! spark plug anti-fouler. It didnt' appear that there was much room for any gasses to get around the sensor, so I took another shot with the spare one I had. I drilled this one out to .5" again and then attacked it with my dremel and a grinding cylinder. I nibbled away a significant amount more material and it looked closer to the diameter of the PDM extender that Flat4 sells.

I installed both the new sensor and the extender together last week and have yet to see the CEL come back. I have put a couple hundred miles on the clock so far in mixed driving conditions. While this wasn't exactly a scientific experiment, the extender may have done the trick. I guess time will tell. For now though, no more CEL!!!
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Old 06-11-2004, 06:27 AM   #2
bigdweeb
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Welp... I knew I spoke too soon. On my way to work this morning it came back on I guess I will get it pulled tonight and see where I go from there.
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Old 06-11-2004, 01:59 PM   #3
00RScoupe
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Wow, sounds like what I have experienced, except I actually tried the MIL eliminator first.

The Flat 4 extender seems to work for me, in that I can go longer distances betweend the dreaded P0420. I am going even farther between CELs now that I have moved and am doing much less highway driving.

Keep us updated if you come up with anything.

I think you and I might just be suffering from the oversensitive computer that many of the early MY00 have been known to exhibit.
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Old 06-11-2004, 02:21 PM   #4
bigdweeb
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00RSCoupe:
Yeah... it seems we are experiencing basically the same thing. Thanks for your long threads about this btw. It's what got me going on trying to fix the damn thing.

I am going to pull the code tonight and make sure it's what I suspect, PO420. If that's the case, I may try resetting it and seeing how long I can go a second time. If it proves to be about the same amount of time, I may try the Flat 4 extender like you have. If that gives the same results, I don't know what I'll do. I may swap the Borla headers out for the stockers and giving that a run. If that solves it, I guess I will have to consider wrapping, coating or ditching the Borlas...
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Old 06-12-2004, 07:40 AM   #5
FstEddie22
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Don't bother experimenting with the Flat4 Extender. I, along with many others, pulled the CEL eventually anyways. Supposedly you can go long distances, but in the end, it doesn't really matter if you're just going to keep getting it. I say save your $26 (yes they charge a big chunk for shipping) and wait for the Cobb Access Port or I-speed relash. Word is, is that both of them are supposed to be ready by the end of summer (August), but we all know how that is.

Ed
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Old 06-12-2004, 08:17 AM   #6
bigdweeb
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hrmm... I still have to get the code pulled, but yeah maybe I won't try the Flat4 extender. I have a feeling the one I fabricated wouldn't be significantly different to change anything. The only thing that was different yesterday morning was that it was really cool compared to the weather we have had lately... it was in the low 50s whereas the rest of the week had been in the 70s. Maybe the dip in temperature was enough to set it off. I may just try swapping the stock headers back on at some point when I get a chance and see if that cures it.

Cobb is working on AccessPort for us? Really... I wouldn't hold my breath on it being on time or cheap. What would that do exactly? Would it just shut off the PO420 code or would it remap the ECU to look for different voltage values from the rear O2 sensor?
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Old 06-12-2004, 10:17 AM   #7
FstEddie22
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Just pull the code and if it is the 2nd o2 sensor, everyone says it isn't a big deal. You shouldn't have to swap the original headers back on. Can someone please explain exactly what the 2nd O2 sensor does? If it doesn't effect the way the car runs, is it just for envriromental purposes?

As for the Cobb Access Port, I'm not sure if it is an AccessPort or a reflash. There are threads on it on their website forum, I'm just too lazy to check right now on this 56k computer. I think they remap the ECU, but I'm not sure exactly what they do to it. Again, you can probably find out on the Cobb website. Hope this helps.

Ed
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Old 06-12-2004, 11:59 AM   #8
00RScoupe
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I think the second O2 sensor is only there to check if the cat is working.

Only problem is that the way the computer works is that it simply measures the difference between front (before cat) and the rear (after cat). The computer thinks the cat is working if it sees a consistent number on the rear.

Once you had headers, and/or a high flow cat the exhaust system is working so much better that the rear O2 will detect fluctuations that it doesnt' normally see on the stock headers/cat. Therefore, even if it is working correctly it will pop up P0420.

If I remember right you can go to Scoobymods and look up Random tech high flow cat, and in that thread there is a much better description of how the computer works and why it doesn't like aftermarket headers and cats.
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Old 07-22-2004, 08:52 AM   #9
DreddRS25
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Dig, Dig, Dig old threads.

Would it be uncommon for the P0420 code to come on for a few days and then go off? My headers triggered a CEL after 3 weeks of being on, CEL for about 3-4 days, and now no CEL. Should I expect that it will come and go?
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Old 07-22-2004, 09:16 AM   #10
bigdweeb
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That's uncommon in my understanding... AFAIK, exhaust codes like PO420 are supposed to stay on until they are cleared. That has been my experience anyway. I have cleared mine a couple times with a scanner and it usually comes back in about a week or so.

As for my "no CEL yet"
I need to do my clutch in a few weeks. I will have to separate my exhaust at that point and am either considering swapping the original exhaust manifold back on or wrapping my headers to see if that helps things. At this point I am thinking of going back to the stock manifold, but that remains to be seen.
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Old 07-23-2004, 07:33 AM   #11
Slack
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I installed the mechanical fix on my car last Sunday and no CEL yet. I have borla headers and a random tech cat, which have caused me to have the PO420 code for over a year with it randomly going off and then coming back on shortly thereafter. So far I haven't had the code come back. I was only able to use 1 of the anti-foulers due to the lack of space between the O2 sensor and the bottom of the car.

From what I've read, the to sensors in your cat section are looking for temperature and/or oxygen content changes from the first and second sensor. If the second sensor doesn't see enough of a change from the first it will throw the code. If that is true, then perhaps wrapping your headers and the first part of your cat section could help by heating up the cat more to burn the gases more thoroughly. It's just an idea, but it couldn't hurt to try it out.



Mick
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Old 07-23-2004, 08:55 AM   #12
DreddRS25
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I have considered wrapping the headers. Just thinking that here in Texas it stays hot enough, so I wasn't worried about wrapping soon. But I am assuming the light going on and off can be a good thing in that the sensor is reading something. Did I read correctly that wrapping headers can shorter their life span and void the warranty?

Hmmm. And those RT Cats are looking better and better. Looks like I'm being counterproductive in preventing the CEL.
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Old 07-23-2004, 03:28 PM   #13
SlimChance
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I have the Brullen Headers w/high flow cat and I am seeing exactly the same behavior. The CEL light will come on, then it will clear itself. Only to come back on later. There doesn't seem to be any rhyme or reason. It will come on when cruising around 50-60 mph in the rain. But it also has turned off, in the same circumstances.

It's good to know, that I'm not the only one.
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Old 07-23-2004, 03:51 PM   #14
Matt Monson
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The reason the CEL is going off is that if the same CEL isn't read in the 5 consecutive driving instances, the car will assume that it was a false code and clear it. So, what you guys are experiencing is sometimes conditions where the readings are out of spec and other times when it isn't. A lot of things could cause that. It could be temp or humidity, or even a new tank of gas with slightly different burn characteristics.

I have the Flat4 extender and it used to work for me for around 500-600 miles between 0420's. Near the end, I started getting the 0136 code as well. Now I have a permanent CEL with the addition of cams. For me, the only fix will be the Accessport, which is slowly progressing. I spoke to Trey about it last week. He wouldn't stick a date on it, but I am thinking it will come out sometime this fall if things keep moving along without any major set backs...
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Old 09-24-2004, 06:20 PM   #15
bigdweeb
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I was driving home from work today and my CEL WENT OUT!!!

I did my clutch last weekend and at the same time swapped out the Borlas for a stock exhaust manifold. All things considered I think I like the sound of this setup better anyways... I must be getting old.

Anyway, I didn't reset the ECU during the clutch install so the CEL was still on. I have only driven the car a handfull of times since the clutch was done, but this time the sensor must have been reading in spec. I am going to watch it for a few more weeks as the weather cools down and if it stays off I think I'm gonna try removing the mechanical fix I made with the HELP! anti-foulers. I'll update this again when things change.
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