O2 SENSOR INFO

[Guest PURPLE95]

During my quest to replace my clutch, I had to pull the exhaust out of my C4 (95) last year for the OBD1 system. I looked at the huge cats under the car and thought, hmmmmm, remove the cats, save wieght and get better flow. There is only one downstream cat, read: after the cats on the OBD1 cars. 96 was the beginning of the OBD2 cars which had 2 downstream sensors. During my research about removing the cats and having to deal with the downstream O2 sensor I found out some great info. The upstream O2's are the only ones that take care of fuel trim. Of course if your going to do any exhaust work you would want to leave those 2 sensors in the system. The downstream sensor is looking at cat convertor performance. Another words, what is coming out of the cat, dirty or clean. In order to eliminate the opportunity for the downstream sensor to be able to get a full or accurate reading, I found an easy and inexpensive way to deal with this. The fix is to install two spark plug anti foulers. The first one just screws into the O2 sensor bung. The second one gets drilled out to be able to receive the size of the portion of the sensor that typically hangs down into the exhaust stream. The drilled out anti fouler gets screwed into the first one completing the "adapter" for the sensor. Install the O2 sensor into the new assembly and plug it into the sensor harness. This removes the sensor from the exhaust stream and "shrouds" it. Now the sensor won't be able to pick up a true reading because it is not directly in the stream. If this is performed and you are getting a mil light the sensor just needs to be further shrouded from the stream by getting a longer anti fouler. It is recommended that you use 2 long anti foulers to begin with. In closing. I am going to perform this mod to my Vette along with a bunch of undercar gasket replacing etc. I will let you know what the result is once the car is running again. Just FYI this isn't something that I just came up with. I researched this for a week and found that this is the best way to achieve a "no mil" scenario without having to deal with an oddball O2 sim. Later, Rich

[JLs Mistress]

During my quest to replace my clutch, I had to pull the exhaust out of my C4 (95) last year for the OBD1 system. I looked at the huge cats under the car and thought, hmmmmm, remove the cats, save wieght and get better flow. There is only one downstream cat, read: after the cats on the OBD1 cars. 96 was the beginning of the OBD2 cars which had 2 downstream sensors.

During my research about removing the cats and having to deal with the downstream O2 sensor I found out some great info. The upstream O2's are the only ones that take care of fuel trim. Of course if your going to do any exhaust work you would want to leave those 2 sensors in the system. The downstream sensor is looking at cat convertor performance. Another words, what is coming out of the cat, dirty or clean. In order to eliminate the opportunity for the downstream sensor to be able to get a full or accurate reading, I found an easy and inexpensive way to deal with this.

The fix is to install two spark plug anti foulers. The first one just screws into the O2 sensor bung. The second one gets drilled out to be able to receive the size of the portion of the sensor that typically hangs down into the exhaust stream. The drilled out anti fouler gets screwed into the first one completing the "adapter" for the sensor. Install the O2 sensor into the new assembly and plug it into the sensor harness.

This removes the sensor from the exhaust stream and "shrouds" it. Now the sensor won't be able to pick up a true reading because it is not directly in the stream. If this is performed and you are getting a mil light the sensor just needs to be further shrouded from the stream by getting a longer anti fouler. It is recommended that you use 2 long anti foulers to begin with.

In closing. I am going to perform this mod to my Vette along with a bunch of undercar gasket replacing etc. I will let you know what the result is once the car is running again. Just FYI this isn't something that I just came up with. I researched this for a week and found that this is the best way to achieve a "no mil" scenario without having to deal with an oddball O2 sim. Later, Rich

What if you just turn off the rear O2 with your tuner ?.....I should ask they do have turners right if not never mind . I might be old but new at this not sure about the C4

[Guest PURPLE95]

During my quest to replace my clutch, I had to pull the exhaust out of my C4 (95) last year for the OBD1 system. I looked at the huge cats under the car and thought, hmmmmm, remove the cats, save wieght and get better flow. There is only one downstream cat, read: after the cats on the OBD1 cars. 96 was the beginning of the OBD2 cars which had 2 downstream sensors.

During my research about removing the cats and having to deal with the downstream O2 sensor I found out some great info. The upstream O2's are the only ones that take care of fuel trim. Of course if your going to do any exhaust work you would want to leave those 2 sensors in the system. The downstream sensor is looking at cat convertor performance. Another words, what is coming out of the cat, dirty or clean. In order to eliminate the opportunity for the downstream sensor to be able to get a full or accurate reading, I found an easy and inexpensive way to deal with this.

The fix is to install two spark plug anti foulers. The first one just screws into the O2 sensor bung. The second one gets drilled out to be able to receive the size of the portion of the sensor that typically hangs down into the exhaust stream. The drilled out anti fouler gets screwed into the first one completing the "adapter" for the sensor. Install the O2 sensor into the new assembly and plug it into the sensor harness.

This removes the sensor from the exhaust stream and "shrouds" it. Now the sensor won't be able to pick up a true reading because it is not directly in the stream. If this is performed and you are getting a mil light the sensor just needs to be further shrouded from the stream by getting a longer anti fouler. It is recommended that you use 2 long anti foulers to begin with.

In closing. I am going to perform this mod to my Vette along with a bunch of undercar gasket replacing etc. I will let you know what the result is once the car is running again. Just FYI this isn't something that I just came up with. I researched this for a week and found that this is the best way to achieve a "no mil" scenario without having to deal with an oddball O2 sim. Later, Rich

JL,

Your right, you can "tune" the ecm to remove the rear O2 sensor(s) from the data stream, but that costs money as it is a function of tuning. The spacing and insulating the rear O2(s) is a cheap but effective way to take care of this problem.

[Cross]

I have known about this for years I think I still have two with one drilled out sitting in my box.

[Guest PURPLE95]

I have known about this for years I think I still have two with one drilled out sitting in my box.

When you put them in the car, did the mil light stay off? The tech's that I have talked to don't actually have seat time in a car with this mod. Any info here will help. Thanks, Rich.