Defouler placements - Lexus IS Forum
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post #1 of 9 (permalink) Old 06-18-2019, 10:26 PM Thread Starter
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Defouler placements

Hello all this is my first post on the forum. I recently installed exhaust headers on my 02 is300, obviously it threw a CEL light. I currently have defoulers with o2 sensors on all four sensors (bank 1 sensor 1 and 2/bank 2 sensor 1 and 2).

The current set up is after market headers(no cat) with stock y pipe (with cat).

So my question is which sensors should I put the defoulers on to clear the code.

i might get a ypipe to help with this issue...

Last edited by Howie Quan Nguyen; 06-18-2019 at 10:32 PM.
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post #2 of 9 (permalink) Old 06-19-2019, 06:20 AM
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I currently have defoulers with o2 sensors on all four sensors (bank 1 sensor 1 and 2/bank 2 sensor 1 and 2).
You don't put them in the primary positions no matter what. The engine uses the primary 02's to run properly. The secondary's only check emissions. They have no impact on how the car runs. ypipe will do nothing in relation to this issue. Anything after the secondary 02 sensors doesn't matter to your problem.

The point of defoulers is to remove the secondary 02 sensors from the primary exhaust flow in hopes the ECU won't notice the missing cats. As to whether they work or not, you'll have to determine that on your own. They worked on older cars but newer ones seem to be less "foolable".

I know that the IS300 is looking for a specific fairly fixed but slightly varying voltage from the secondary 02's. It's actually documented in the manuals.
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post #3 of 9 (permalink) Old 06-19-2019, 12:06 PM Thread Starter
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Originally Posted by Ek9B18 View Post
You don't put them in the primary positions no matter what. The engine uses the primary 02's to run properly. The secondary's only check emissions. They have no impact on how the car runs. ypipe will do nothing in relation to this issue. Anything after the secondary 02 sensors doesn't matter to your problem.

The point of defoulers is to remove the secondary 02 sensors from the primary exhaust flow in hopes the ECU won't notice the missing cats. As to whether they work or not, you'll have to determine that on your own. They worked on older cars but newer ones seem to be less "foolable".

I know that the IS300 is looking for a specific fairly fixed but slightly varying voltage from the secondary 02's. It's actually documented in the manuals.
Okay I removed defoulers from B1S1 and B2S1 and left defoulers on B1S2 and B2S2. will return to thread to update you guys.

Last edited by Howie Quan Nguyen; 06-19-2019 at 07:17 PM.
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post #4 of 9 (permalink) Old 07-06-2019, 12:10 AM Thread Starter
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I removed defoulers from B1S1 and B2S1 and left defoulers on B1S2 and B2S2; I then erased the code. The CEL stayed off for about almost 200 miles then came back on again for the same code. BUT the engine is running much better because the O2 sensors pre cat are reading correctly. been driving with the CEL code for a 400 miles now and nothing is wrong but does anyone know a permanant solution to this?
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post #5 of 9 (permalink) Old 07-06-2019, 12:02 PM
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Originally Posted by Howie Quan Nguyen View Post
I removed defoulers from B1S1 and B2S1 and left defoulers on B1S2 and B2S2; I then erased the code. The CEL stayed off for about almost 200 miles then came back on again for the same code. BUT the engine is running much better because the O2 sensors pre cat are reading correctly. been driving with the CEL code for a 400 miles now and nothing is wrong but does anyone know a permanant solution to this?
Back in the day with my S2000 I had a similar situation. Would stay off for a little but eventually trip. My solution (which actually seemed to work perfectly) was to stack two defoulers on top of each other and then plug the O2 sensor in. I've also seen people get the 90 degree elbow defoulers which would lesson air flow by the o2 sensor. Good luck.
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post #6 of 9 (permalink) Old 07-06-2019, 08:11 PM
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Most people use an active O2 sensor simulator. It's basically a small PC board that emulates the secondary 02 sensor. You still have to leave the sensor heaters hooked up or the ECU will notice it.

200 miles ought to let you get through most emissions tests. You'd need to reset the CELl, drive it just enough to get into readiness then have it tested.
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post #7 of 9 (permalink) Old 07-12-2019, 11:29 PM Thread Starter
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Originally Posted by humbucker87 View Post
Back in the day with my S2000 I had a similar situation. Would stay off for a little but eventually trip. My solution (which actually seemed to work perfectly) was to stack two defoulers on top of each other and then plug the O2 sensor in. I've also seen people get the 90 degree elbow defoulers which would lesson air flow by the o2 sensor. Good luck.
I have extra defoulers so I'll try this I'll get back to you when I can
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post #8 of 9 (permalink) Old 07-12-2019, 11:30 PM Thread Starter
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Originally Posted by Ek9B18 View Post
Most people use an active O2 sensor simulator. It's basically a small PC board that emulates the secondary 02 sensor. You still have to leave the sensor heaters hooked up or the ECU will notice it.

200 miles ought to let you get through most emissions tests. You'd need to reset the CELl, drive it just enough to get into readiness then have it tested.
I'm gonna look into this if the double defouler doesnt work. Is there any link you can direct me toward for my car?
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post #9 of 9 (permalink) Old 07-13-2019, 11:02 AM
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Originally Posted by Howie Quan Nguyen View Post
I'm gonna look into this if the double defouler doesnt work. Is there any link you can direct me toward for my car?
Just get a simulator and call it a day.
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