Bad O2/Cat Relationship

[Vettezuki]

I have a situation on the Aveo from hell, where I know the O2 sensors are bad because the computer will throw a code immediately after clearing it. Here's the question:

If know the O2 sensors are bad, but don'tkow if the cat is bad, what's the best way to proceed? My understanding is that a bad cat can wreck at least the downstream O2 sensor, and if the ECU gets bad data, it can also lead to a condition where both O2 sensors get toasted.

All I know to do is put in the new O2 sensors, but I'm not going to be happy if they get chewed up right away. How can I avoid that?

[Damian]

Before you change the O2 sensors out, you can run the engine for awhile and then use a temp gun to see what the temps are right before and after the cat. If its hotter before the cat, it's bad.

[BADDASSC6]

Check the part numbers on the O2 sensors. If they are the same than a bad cat will not damage the downstream O2 sensor. O2 sensors are $50 to 100 I would just replace it and see what happens.

[Vettezuki]

Check the part numbers on the O2 sensors. If they are the same than a bad cat will not damage the downstream O2 sensor. O2 sensors are $50 to 100 I would just replace it and see what happens.

They're different and quite a bit different in price. Don't know if that's just the length of the pigtail, or something else, but they ain't the same part.

[94cobra69ss396]

Like Damian said, check the cats with a temp gun. Run the engine at around 3000 rpms for a couple minutes and then check the temp before and after the cat. The temp out of the cat should be about 300 degrees hotter if the cat is working properly.

[Vettezuki]

Thanks for the cat check protocol. I shudder at having to replace that as the cheapest cats are fuck all expensive.

[94cobra69ss396]

That's where I'm at on the Cobra. I think I'm going to add front cats to the current H pipe which are about $130 each. A complete four cat H pipe is about $550. I might be able to get a stock one that's missing a front cat but I don't know yet. I haven't tested my cats yet but my current H pipe only has 2 cats.

[Vettezuki]

The one (1) cat on the Protege was like $750. I think they are like $650 on the LS1 AIR. It's not total BS though, OEM cats have a lot more catalyst and platinum in them than aftermarket, which borderline isn't even legal anymore. The law is pretty fuzzy to me. Paul would know, but in the Aveo case, basically a dealer item.

[Shaolin Crane]

That's where I'm at on the Cobra. I think I'm going to add front cats to the current H pipe which are about $130 each. A complete four cat H pipe is about $550. I might be able to get a stock one that's missing a front cat but I don't know yet. I haven't tested my cats yet but my current H pipe only has 2 cats.

I never used the cats you gave me. You're welcome to them back.

[Leedom]

Give me the part numbers for the O2 sensors and I will check to see if we manufacture them. If we do I might be able to get you a good price on them.

[Damian]

You can get cats that are OBDII compliant. They have the CARB number or whatever number stamped onto the housing. Or try eBay.

[Vettezuki]

Well, not exactly sure where to check temp in my exact case, but nowhere lower on the cat, or exiting the cat to the exhaust flange is the temprature higher than at the collector. It's the same or cooler. But that doesn't surprise me given the configuration. The collector and entry point is in front of the engine behind the radiator. The bottom/exit is probably in the air sufficiently to get cooling to the atmosphere and isn't directly mated to as much thermal mass. So it' either toast, or that test is not so relevant in the case of the Aveo. :huh:

NOTE: cat comes straight off the exhaust manifold is what I'm getting at. It's not located under the car.

[Damian]

Maybe try driving it around the block a few times and then check it. Keep it idling while you check. But if it has no power like you said it doesn't, chances are the cat is bad.

And if the cat is bad, change it out first before you change out the O2 sensors.

[Vettezuki]

Maybe try driving it around the block a few times and then check it. Keep it idling while you check. But if it has no power like you said it doesn't, chances are the cat is bad.

And if the cat is bad, change it out first before you change out the O2 sensors.

After changing out the gas and plug wires, power is about where I'd expect of that little 1.6L. :huh: