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Old 09-07-2012, 05:31 PM   #1
afraziaaaa
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Modified 2005 ST P0420

Ok, so I fixed the last code that I had (P2004) with new vacuum lines.

Now, I am trying to get a NJ inspection (never move to NJ if you have a modified car unless its more than 25 years old).

I had to detune the car to the stock tune because none of the electronic monitoring systems would show up as "READY" for the inspectors while it was running on aftermarket tune. So now, it runs, but I have CAI, 2.5" exhaust and Crane stage 1 cams so I am most likely incredibly lean. Once all the systems reset, the code P0420 came up. It basically means that the cat isn't working properly.

So, my plan is to go back to stock cams and see if the code goes away.

Two questions:

1. Has anyone experienced this or a similar scenario?
2. If the code does not go away once I replace the cams, is it still possible that I have a bad downstream O2 sensor?

I have already looked all over the internet for information and found what I needed. I am not looking for info, but more for anyone's personal experiences and tips/tricks to get this fixed without having to drop several hundred dollars for a new exhaust manifold.

Once I get the car fixed and inspected it is going up for sale, along with several of the bitchin aftermarket parts I have for it. I needs me a truck!

Thanks for looking and for any advice.


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Old 09-08-2012, 03:51 PM   #2
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Not a soul, eh?
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Old 09-08-2012, 04:46 PM   #3
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Since P420 is a catalyst problem, I'm not sure why you're thinking a cam swap would rectify the code? If the cat is truly done and it's not a downstream O2 sensor/ sensor wiring issue, you could try using a MIL cheater (either the electronic kind or one that simply pulls the sensor out of the exhaust stream) to defeat that one code.
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Old 09-08-2012, 04:55 PM   #4
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To my knowledge they don'take o2 sims anymore
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Old 09-08-2012, 05:04 PM   #5
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You can make your own:
http://www.focusfanatics.com/forum/showthread.php?t=130381
Principle is simple. Introduce the voltage drop that the ECU is looking for by some other means or remove the sensor from the "dirty airflow" (mechanical method - can't find a link but it involves using a plug de-fouler.)
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Old 09-08-2012, 06:28 PM   #6
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FWIW, BC's got the right idea!

it's been discussed in the "tuning" forums - IF both cat sensors are working properly, the 'downstream" one needs to see "cleaner" exhaust than the "upstream" one to let the computer know the Cat is functional.

SO, 'cheating" by moving the downstream further out of the exhaust flow, like by screwing it into a "spark plug anti-fouling" adapter will "fool" the computer, letting you "pass" emissions testing....

Luck!
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Old 09-09-2012, 05:36 AM   #7
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Quote:
Originally Posted by sailor View Post
FWIW, BC's got the right idea!

it's been discussed in the "tuning" forums - IF both cat sensors are working properly, the 'downstream" one needs to see "cleaner" exhaust than the "upstream" one to let the computer know the Cat is functional.

SO, 'cheating" by moving the downstream further out of the exhaust flow, like by screwing it into a "spark plug anti-fouling" adapter will "fool" the computer, letting you "pass" emissions testing....

Luck!
You said exactly the words that I needed to hear. I have an extra bung welded into my exhaust manifold after the flex pipe. I am going to try moving the rear O2 back there and see if it reads any differently. Hopefully that will at least get me to pass inspection so I can have a bit more time to scrape some dough together for the new exhaust manifold.

BC, I guess you are right that the cams will not change it. After hearing your explanation, I realize that I was hoping the cam swap would be a less expensive alternative to replacing the exhaust manifold.

Either way, I plan on selling the car once its fixed up and most people don't want an idle that lopes from 650-850 on a stock tune. It purrs well on the aftermarket tune at 1000rpm, but can't pass inspection that way. NJ and EFI cars are a bad combo for enthusiasts.
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