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Old 09-20-2008, 11:41 AM   #1
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02 Boxster S header/O2 help?

I recently put on a set of headers which increased the pipe diameter and removed the primary cats on my 2002 Boxster S. The bad news is that after 150-200 miles the CEL came on. I initially installed the O2 sensors in the runners of the new headers (not at the collector) and had a couple bungs welded in past the second set of cats. I extended the wire for the second set of O2 sensors using crimp connectors. I initially thought that the one of the O2 sensors was bad so I replaced it with a Walker sensor. After another 150 miles the CEL came on again. I thought maybe I should move the O2 sensors down to the collector area of the headers so I extended the wires on the sensors and screwed them in. After 150 miles the CEL light came on yet again! The codes are P0133 and P0153 which are aging pre-cat sensors (the MAF code also showed up). Meanwhile I also installed an Agency Power CAI (after the first CEL showed up so I don't think it is the MAF?).

derb helped me looked at what is going on with his Durametric tool and the post-cat sensor on the drivers side wasn't fluctuating its voltage.

Help? Is it possible that I fried the front sensors when I had them installed in the runners of the new headers? Is there something I am missing? It looks like I'll be purchasing some more O2 sensors but sure would like to know what went wrong? I really like the sound of the new headers and believe I have gained some power at higher RPM's but am not going to drop $$$ in a bunch of sensors trying to make it work.


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Old 09-20-2008, 04:30 PM   #2
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Boy does this sound like a familar story. When I put on headers and high-flow cats I ended up replacing my oxygen sensors, redoing the wire extension to the rear sensors and even replaced both my cats. Every time we tried something, I was still getting a CEL after 100 miles or so. We tried moving the location of the sensor bungs, moving the sensor into and out of the gas stream, still got CEL. I find it interesting that some folks put on headers and extend the wire to their oxygen sensors and never get a CEL, not me.

In my case, the shop that installed the headers and high-flow cats also wrote the software for, and installed the chip in my car. They ended up going into the ECU and slightly changeingthe threshold whereby the CEL was triggered. It has been 15K miles and the car is running like a top and no CEL. BTW, all the time I was getting the CEL, the car was still running great, the light just drove me nuts. Best of luck with your CEL, not sure what to offer other than what my experience was,


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Old 09-20-2008, 05:23 PM   #3
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Maybe a larger gauge wire for the sensor extension will lower resistance enough to keep the signal to the ECU within the expected range?
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Old 09-20-2008, 05:41 PM   #4
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Here is the description of the codes from the Durametric Tool:

P0133 - Porsche fault code 15 - sensor ageing behind cat (conv. cylinder (1-3) below limit value)

P0153 - Porsche fault code 21 - sensor ageing behind cat (conv. cylinder (4-6) below limit value)

This is saying that the voltage on your post-cat O2 sensors is too low. Are they in the stream of exhaust gas? I know when I initially put headers on I just tied up the sensors in the engine area and didn't put them in the exhaust flow. I got both of these codes because the O2 sensor wasn't reading any exhausts gases. The engine computer was smarter than I thought.

If the catalytic converter is doing its job, the voltage should read a lower voltage than the pre-cat O2 sensors. You'll see major flucuation in the pre-cat O2 sensors from between .1 to .8 volts. I haven't driven the car much since putting my post-cat O2 sensors in on the car and extending the O2 wires, so I can't comment on the voltage yet for my post-cat O2 sensors and if any CEL will go off. So far though, nothing yet.
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Old 09-22-2008, 03:34 AM   #5
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just find a Porsche PST2 and have someone scan your DME to ROW
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Old 09-22-2008, 07:10 AM   #6
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When you extend the oxygen sensor wires you must ensure that the signal wire and the signal ground wire are extended as a twisted pair.

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Old 09-22-2008, 02:42 PM   #7
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Originally Posted by tholyoak
When you extend the oxygen sensor wires you must ensure that the signal wire and the signal ground wire are extended as a twisted pair.

Interesting advice... what is the reason for the twisted pair? Can I simply twist everything including the heating wires? Thanks!
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Old 09-29-2008, 09:44 PM   #8
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Wow, seems like a lot are having problems with the headers.I have 2003 s, I also put headers and I keep getting the cel. I put in spark plug non fowler p/n 42002 last weekend and drove it about 100-200 miles, so far the light has not come back yet. you can get this part in any parts store. you need to buy 2 sets and drill the other one. you can google it and get more information or you can pm and i will send you more info.
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Old 10-05-2008, 08:07 AM   #9
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In general twisted PAIR wiring is used to cancel interference and must be bought already twisted, it's not something you can just twist by hand.
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