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Hi all, new here. Read a few of the threads regarding O2 sensor bypassing and etc. Everyone seems to keep acting as if there is only one cat on the 96-00 Civics? Mine has two... One in the manifold, and a smaller one welded in place down the middle of the car. I'm not wanting to replace the things. I was just wanting to buy a cheap header and pull off the rest of the exhaust (run it open)... However, I want my CEL to be working and off. Figured it was easy as throwing an O2 simulator in the bung hole on the downpipe... The pipe has an EX down pipe but that shouldn't matter if I'm scrapping the back half of the exhaust right?
 

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yea just put your front o2 sensor in pre "cat"

then use the sparkplug non fouler trick or buy the ones you can get on ebay. put your rear o2 sensor in that.

basically need the rear o2 to read less exhaust than the front one and cel should stay off. i can tell you from experience that the light may show up some times and you will need o just clear it out and it will stay gone for a while but may come back.
 

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What is the "spark plug non fouler trick"?
They make nonfouler adapters that limit the amount of exhaust gas that the 02 sensor can read. So when you use the adapter on the secondary 02 with a cat delete, the secondary 02 wont read a large enough difference between the primary 02 to throw a CEL



Many local parts store stock them.
 

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Discussion Starter #6
What is the "spark plug non fouler trick"?
They make nonfouler adapters that limit the amount of exhaust gas that the 02 sensor can read. So when you use the adapter on the secondary 02 with a cat delete, the secondary 02 wont read a large enough difference between the primary 02 to throw a CEL



Many local parts store stock them.
There is only one o2 bung on the downpipe, should I tap it for a second one?
 

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It's the Y7 exhaust so one is built into the manifold and the other is welded into the middle of the exhaust halfway down the car otherwise I would have went that route. I will be going that route with my wife's Caravan lol... As it is, I'm taking a cutoff wheel to the exhaust and pulling everything then replacing the manifold to just run open header...
 

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Hi all, new here. Read a few of the threads regarding O2 sensor bypassing and etc. Everyone seems to keep acting as if there is only one cat on the 96-00 Civics? Mine has two... One in the manifold, and a smaller one welded in place down the middle of the car. I'm not wanting to replace the things. I was just wanting to buy a cheap header and pull off the rest of the exhaust (run it open)... However, I want my CEL to be working and off. Figured it was easy as throwing an O2 simulator in the bung hole on the downpipe... The pipe has an EX down pipe but that shouldn't matter if I'm scrapping the back half of the exhaust right?
Do you have 1, 2 or 3 "lumps" in your exhaust? Lump meaning round catalytic converter looking devices.

1 lump is definitely the cat.

2 lumps could be two cats or 1 cat and 1 resonator

3 lumps could be 2 cats and 1 resonator.

If your car has a manifold mounted lump, it is almost always a cat. Any lumps following the manifold mounted cat can usually be determined by their heat shield design.

If the heat shield looks something like the attached pictures labeled "heatshield", that is catalytic converter heatshielding. If the shielding is plain, smooth or simply not there and the lump is more than half way towards the back of the car, you are most likely looking at a resonator chamber.


Are the cat(s) clogged or just not working normally? Do you keep getting a P0420? If they were clogged, you would be suffering engine performance issues. If you just keep getting a fault code, more than likely the catalyst materials have simply degraded and it is no longer efficient. Your engine performance won't suffer simply because of catalyst degradation. Clogged cat(s) should ALWAYS be replaced, otherwise your engine will not be happy.


What engine/trim level civic do you have?

If you have a manifold mounted catalytic converter, you most likely have the OEM upstream wideband oxygen sensor setup. There were two different versions of upstream oxygen sensors that you could have.

The wideband version was usually reserved for use on certain VTEC-E and economy non-VTEC engines with a manifold mounted catalytic converter for tighter catalyst operation control and fuel control on the economy trim levels.

The more "performance" oriented civic variants came with a normal upstream narrowband heated oxygen sensor with a regular header style manifold. The catalytic converter and sensor set was further downstream.

You are sure you have two catalytic converters installed, and the second one you are looking at isn't just a resonator pipe? See the attached pictures, and let me know which possible exhaust configuration you have.


Just an FYI about the non-fouler trick, because I have run into this with customers asking for exactly what you are trying to do with the manifold mounted setup:

If you DO have the wideband upstream sensor setup, the catalyst monitoring downstream O2 sensor is still just a normal narrowband O2 sensor BUT the catalyst operating/monitoring strategy is MUCH more tightly scrutinized by the ECU. If you do attempt the spark plug non-fouler trick on the downstream O2 with this setup, it MAY or MAY NOT work. Most of the time, the light will stay off for longer but it DOES come back on.

Best way to determine if you have the wideband upstream O2 variant with the manifold mounter catalytic converter is to check the part number of the upstream sensor. Use a Honda parts catalog website (there are many) and pull up the exhaust system parts diagram. Compare your sensor P/N with what the diagram shows. There will be upstream sensor part choices based on P/N, one will be much more expensive than the other. If you match to the more expensive one, it's the wideband variant. If you match to the less expensive one, its the narrowband variant.

The above is just to give you an idea of what to expect when trying to "trick" the ECU. You might still be fighting the CEL even after any tricks.
 

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Discussion Starter #10
Yes there is one after the first cat, the first cat being part of the manifold (D16Y7), I don't want to replace cats, just open header... So, a 4-2-1 header with an EX downpipe on my DX with a bung for the O2 sensor in the downpipe.
 

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Discussion Starter #12
Do you have 1, 2 or 3 "lumps" in your exhaust? Lump meaning round catalytic converter looking devices.

1 lump is definitely the cat.

2 lumps could be two cats or 1 cat and 1 resonator

3 lumps could be 2 cats and 1 resonator.

If your car has a manifold mounted lump, it is almost always a cat. Any lumps following the manifold mounted cat can usually be determined by their heat shield design.

If the heat shield looks something like the attached pictures labeled "heatshield", that is catalytic converter heatshielding. If the shielding is plain, smooth or simply not there and the lump is more than half way towards the back of the car, you are most likely looking at a resonator chamber.


Are the cat(s) clogged or just not working normally? Do you keep getting a P0420? If they were clogged, you would be suffering engine performance issues. If you just keep getting a fault code, more than likely the catalyst materials have simply degraded and it is no longer efficient. Your engine performance won't suffer simply because of catalyst degradation. Clogged cat(s) should ALWAYS be replaced, otherwise your engine will not be happy.


What engine/trim level civic do you have?

If you have a manifold mounted catalytic converter, you most likely have the OEM upstream wideband oxygen sensor setup. There were two different versions of upstream oxygen sensors that you could have.

The wideband version was usually reserved for use on certain VTEC-E and economy non-VTEC engines with a manifold mounted catalytic converter for tighter catalyst operation control and fuel control on the economy trim levels.

The more "performance" oriented civic variants came with a normal upstream narrowband heated oxygen sensor with a regular header style manifold. The catalytic converter and sensor set was further downstream.

You are sure you have two catalytic converters installed, and the second one you are looking at isn't just a resonator pipe? See the attached pictures, and let me know which possible exhaust configuration you have.


Just an FYI about the non-fouler trick, because I have run into this with customers asking for exactly what you are trying to do with the manifold mounted setup:

If you DO have the wideband upstream sensor setup, the catalyst monitoring downstream O2 sensor is still just a normal narrowband O2 sensor BUT the catalyst operating/monitoring strategy is MUCH more tightly scrutinized by the ECU. If you do attempt the spark plug non-fouler trick on the downstream O2 with this setup, it MAY or MAY NOT work. Most of the time, the light will stay off for longer but it DOES come back on.

Best way to determine if you have the wideband upstream O2 variant with the manifold mounter catalytic converter is to check the part number of the upstream sensor. Use a Honda parts catalog website (there are many) and pull up the exhaust system parts diagram. Compare your sensor P/N with what the diagram shows. There will be upstream sensor part choices based on P/N, one will be much more expensive than the other. If you match to the more expensive one, it's the wideband variant. If you match to the less expensive one, its the narrowband variant.

The above is just to give you an idea of what to expect when trying to "trick" the ECU. You might still be fighting the CEL even after any tricks.
I have a 97 Civic DX sedan with the D16Y7 1.6L non-VTEC. One cat is part of the manifold. There is an O2 sensor right above it. I don't think my second cat looks like either of those, just smooth. I'll check again soon.
 

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Discussion Starter #13

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You can install just about any D series header on your engine, the tricky bit is going to be trying to keep the CEL off.

Regardless of the header you choose, you need to make sure you have the upstream sensor installed. Especially for OBD2+ vehicles, fuel control is dependent on that sensor in closed loop operation.

Let me know what happens in your attempts to trick the rear one! Research the non-fouler trick. I have no idea if there are rear O2 simulators or not for your application.

If the CEL keeps coming back after all your attempts, short of doing a Y8 head swap with a matching engine harness and O2 sensor set, I think putting an aftermarket cat back on will be your cheapest option to keeping the light out :)

Just warning you again, everytime I have tried to trick the version with the upstream wideband setup with the non-fouler trick, it eventually determines catalyst efficiency is not good enough and back comes the P0420. The software is just that much more particular about catalyst operation.

Except for very specific vehicles below 2010, the non-fouler trick works just about every time for about every vehicle. The exceptions are usually vehicles that use rear O2 sensors as part of engine fuel control/catalyst temperature control strategies (your Honda doesn't in this case, it's just super sensitive if it's the upstream wideband version).

Check the O2 part number with the Honda parts website to see which version upstream sensor you have. You might luck out and have the cheaper sensor. I can't tell without being there or without pictures :)

This is not relevant to your situation, but a friendly FYI for future cat removal endeavors :)
From 2012 and newer vehicles, rear O2's in almost every vehicle are used as part of other monitor calculations that extend beyond just catalyst efficiency. Bottom line for these vehicles means the cats MUST be present for proper rear O2 feedback, as proper base engine operation is dependent on correct feedback from them. The system has to work as a whole, or it falls apart and you get faults, which means you can't pass e-test and get your sticker.

Newer vehicles are extremely sensitive to catalyst operation, they watch em like a hawk. There are no tricking new vehicles without a comprehensive solution short of somehow disabling catalyst monitoring within the ECM software. Even this contains huge obstacles, both skill and legal based.
 

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Discussion Starter #16
Will the P0420 inhibit proper engine performance? I know they're clogged because I can't get over 55 mph or the tiniest of inclines... Tech at parts store told me what code meant but not exact code...
 

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P0420 will not inhibit engine performance. It is only an ECU indicator that means the catalyst failed tests that determined it is not operating efficiently.

Now there are many issues that can cause a vehicle to have low power, what kinds of low power diagnostics have you performed?
 
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