What does this mean?

[benfrogg]

So I noticed a 2-5mpg drop in typical trips the past couple of days. Then I noticed this mostly white, slightly yellow residue on the joint of the exhaust mani to the cat.




I know white smoke means burning oil. I know this indicates leaks at this union. (I think?) I know that leaks at the 02 are bad for FE.

What do you guys think?
How can I get this union apart so it can be reassembled with a new gasket? Gasket cement instead?
Thanks
B

[GasSavers_Erik]

Burning oil usually has a blue tint to it, white smoke means moisture (normal when it is cold outside and the exhaust is still cold) or coolant.

I had a leak at that joint on mu 87 Civic. Start soaking them now with penetrating oil and hammer on the correct sized 6 point socket. If the one on the left gets rounded off, you can try to pound on a 12 point SAE socket that is a size smaller or you may need to weld a larger nut over that nut.

[benfrogg]

What kind of effect did this leak have on your fuel mix/ FE since it's right at the the 02? It seems like a bad place for it to happen. Did you just replace the gasket with a new one and that sorted things out?
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[GasSavers_Erik]

My gasket was blown out- it was very loud. Yes I simply took it apart and replaced the gasket- it had a metal inner ring surrounded by a composite outer part. I was able to get it from an auto parts store- although it was special order. I scraped both mating surfaces and it sealed nicely.

Yes- I think that it could affect the mix being that close to the o2 sensor.

[benfrogg]

Well, I tore into it today. The dealer is the only place to get that gasket, $18 and it'll be here in the morning. Here's what it looks like from the top side:

Here's some noticeable damage on the inside of the bottom:

Here's a perplexing pile of what I assume is ash from unburned hydrocarbons:


This stuff fell out when flipped the cat over to unbolt the lower flange. There's a lot of it. Easily enough to fill the palm of my hand.
So, that could have easily been blocking flow. I used an air compressor to blow out any more of that stuff that I could. At least i was able to get this junk cleaned out of the cat..... maybe it was blocked and wont be as much now?
Here's hoping I can assemble it all with no leaks. I bought 4 new nuts ($1.20 each!) and I've got washers that'll work here already. I'll have to put some new SAE bolts in the lower flange after i back out the threaded studs.

I'll report back when I get some more data.
Thanks for the input.
B

[benfrogg]

Just found this:
"If the front oxygen sensor has been replaced and the vehicle still sets a P0420 code, the catalytic converter may be at fault and should be replaced if it cannot be brought back to working operation. Monitor the rear oxygen sensor at cruise to determine if it is cross-counting like the front one. This would confirm the converter is not working. It may be possible to revive the catalytic converter by heating up the converter.

To do this, operate the vehicle until it reaches normal temperature. Ground one spark plug wire and run the vehicle for three minutes at 3,000 rpm. This will cause the catalytic converter to run very hot, which can clean out the contamination and bring the converter back into operation.

I know techs who have performed this procedure on their own vehicle and nine months later, it was still working perfectly. Be aware though, that this may not work on all affected vehicles. "

From here:http://www.asashop.org/autoinc/june2007/techtips.htm

I might try this after I get things put back together.
Can't hurt, right?
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[GasSavers_Erik]

Hmm- did it feel gritty like sand? If so, maybe it was powdered ceramic from some of the honeycomb material inside the cat that degraded over time.

You should also be able to look in one side and shine a light through the other side. This can be done to be sure there are no random blocked passages.

[benfrogg]

Yeah, gritty. Very similar to play sand.

With a flashlight, I can almost not see through any parts of it. In a pitch black room with and a high power led I can see some spots of light through, but not much.

I'm guessing all of this means the cat is way plugged up.
I have a pressure tester for compression that has an adapter that will fit in the 02 sensor hole. If I see like 15 psi or something I'll know what the problem is. I guess it's time to start pricing cats....
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[benfrogg]

Prices I'm finding are about $200ish. Maybe it would be cheaper and better to go with a header and cheaper aftermarket inline cat instead.... I know universal cats can be had for $50-$70.
Has anyone done this mod on a VX? I think I've seen some pictures somewhere on the site of a user that did it.
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[GasSavers_Erik]

If you wanted to save the expense of a header, I think you just could knock a 1.5 inch hole through the center of the ceramic honeycomb and then put an inline cat downstream under the car.