I had the OEM one when I put the headers in but I was getting the MIL. So I went to Advance Auto Parts and grabbed Bosch's OEM version of the O2 sensor. It was cheaper then buying from the dealer and comes with a warranty. Think the dealer has a better O2 sensor?

Install the cat backwards? Hmm. When I had the flanges welded on the, the guy asked me about this. I asked the parts store and they did not know anything. There were not any arrows indicating in and out. Everybody has told me that the MIL comes on because of the high flow cat, not b/c of a bad sensor. This sounded right because I have tried several different sensors with no luck.

 

I would suggest using the OEM sensors that were on the car when you bought it, and double checking the wires again.


There SHOULD have been arrows on the cat .. or at least IN / OUT markings.

If you've double checked the wires, and you've tried different sensors, then honestly I would say the cat might be installed backwards and the CEL you are getting is because the cat is NOT doing its job.

Where did you purchase this cat from?

 

That kinda sucks because the OEM sensors are kind of expensive, but at this point I just want the problem resolved. But the bottom line is, I can have headers and a high flow cat without the MIL on, correct? I thought that I would be selling those headers just to fix this problem. I will try to get this setup up and running this weekend. I will update you with my results probably on Sunday.

I purchased the cat from A&A in Stroudsburg, PA. It looked like a good deal: small and compact, high flow, and EPA approved.

 

Do you have an o2 bung IN your cat?

Because if it's installed backwards, that means you bought the wrong cat, it would mean you bought a cat with an o2 bung in FRONT, when you need one in back. Go to the place you bought it from and find the exact one you bought, then ask them if the o2 bung is in the front or back, this will tell you if you have the cat installed backwards or not.

Seriously bro, any o2 sensor SHOULD work, but it's just that I would suggest going the OEM route so you KNOW 100% that the wires match up, because the colors will match, that way you just eliminate the possiblity of you screwing up the wiring being the issue you're dealing with.

Yes, you can have this setup without any CEL.

 

You really should have the first o2 sensor after all 4 collectors merge, that gives the comp incorrect information the way you have it.

 

Ok. The cat I bought just had 2.25" piping coming from both ends. I told the welder to put an O2 bung at one end. He had somebody look at it and they determined which end was in, and which was out. The cat and the box the cat came in did not have any diagrams, symbols or any other types of markings that would show which was in or out. I was also told that a cat installed backwards would not allow the car to run at all. Something about bad flow?

About the first O2 sensor, the car seems to run good, but I will move it after where the collectors merge. That might be why the second O2 sensor is not working. If the first O2 sensor is giving values that are slightly off, that might affect how the ECU handles the second O2 sensor? I am just guessing from what I have read.

So, this weekend, I am moving the front O2 sensor after the collectors. Then, I will re-wire a brand new second O2 sensor completely and hook it up. I should not have any problems with the wires this time. Since hooking up the headers, I have picked up a 2001 shop manual and the Electrical Troubleshooting Manual. This should make everything work correctly. I will also check out the cat again and see if that is an issue. That should be it, I hope.

 

No, don't move the first o2 sensor. STOCK the sensor sits in one runner, it won't make a difference. If your first o2 sensor was giving you bad readings, and you had a CEL, your car would go into limp mode. Throttle response would be low and MPG would suck.

I'm almost positive your problem is that the cat was installed backwards, and the bung welded in the wrong end.
OR
You screwed up the wiring to the 2nd o2 sensor.


To say that a backwards installed cat would not allow the car to run is silly, have you ever looked inside a cat? It's not air tight, therefore air can go in and come out, it just doesn't function properly (ie CLEAN the air) if it's backwards. That's why you're getting a CEL, because IF both of your sensors are functioning properly (ie you wired them CORRECTLY), then both of the sensors are getting a reading which is very much the same, when they SHOULD be getting different reading because the cat is supposed to take some pollutants out (but its not because the cat is backwards, see where I'm going..).

 

Stock o2 sensor sits few inches below Cylinder #4... The air from all cylinders is pretty much all together there. Its not the best position, but it'll do. If his (SSA header I guarantee) is in the actual collector, then it could create problems. Several members here had problems with the SSA header giving CELs, and this is one of the reasons.

I'm not saying this is the problem, but its a cheap fix and can only make the car run better, not worse.

 

Well, I pulled out the stock manifold and the first O2 sensor sits centered on top of the Calif. emissions cat. It does sit where all four runners collect, but thats only like 6 inches away from the top of the manifold. When looking at my engine from the front bumper, the first O2 sensor sits on runner #4 (very last one on the right). If I move the first O2 sensor, it will be after the flex pipe, right before the flange that connects to the cat. I guess I could give it a try and see if it works. It is still recieving information before the cat so it should not mess anything. Does this sound right?

Anyway, at this point I am really more concerned about the second O2 sensor. I can not stand driving with the MIL constantly lit. I am going to try what zoned019 told me to do, and see if that fixes the problem.

By the way, I did look inside the cat and both ends look exactly the same. If you hold it up to the light, you can see through, but not very much (If i can remember correctly). You can only see that light exists on the other end. This made it tough for me to determine what end was in, and what end was out.

 

This is what I would do, in order.

1. Check your wiring on your second 02.
2. Check the placement of the first o2 sensor.
3. Then tear it apart and see if cat was on backwards.