Clamping on catalytic converter

[zaid3ssaf]

My 02 Bravada is throwing a P420. Live data for the oxygen sensors show sensor "mirroring" where both sensors follow the same trend. it still does 19 mpg on highway and I don't think I have any issues with reduced power.


1) How do I know if the catalytic converter is bad or clogged, or of the oxygen sensor is bad
2) What engine problems can cause the cat to die on the 4.2L vortec?
3) Can I cut the old cat out and just clamp a new one on?

 

[Mooseman]

1) How do I know if the catalytic converter is bad or clogged, or of the oxygen sensor is bad

You could use an IR temp gun. Keep the engine revving at 2000rpm and check the temps in and out of the cat. The out temp should be much higher than in temp as the cat burns the gases.

2) What engine problems can cause the cat to die on the 4.2L vortec?

Misfiring engine, old age, mileage, damaged or missing internal honeycomb, contamination by an additive.

3) Can I cut the old cat out and just clamp a new one on?

Sure but finding one that fits right might be difficult as the size is an oddball 2.75" instead of a standard 2" or 3". You might be able to weld in a 3".

 

[Mektek]

When you hit the gas hard to accelerate for an on-ramp the engine will stumble and the check engine light might flash as well. That's a pretty good indicator of a clogged cat.
Since you don't have reduced power, it's probably not clogged.
You might just have a coating of some kind on the catalyst. I think there may be a procedure to clean the cat - superheat it to burn off the contaminants. Maybe someone here knows something about that.

 

[Maverick6587]

I have a car that I'm currently selling that has a catalytic converter code. I'm about to dump a bottle of the CRC Guaranteed to Pass fluid into the tank to see if that "clears it up."

I don't think I would use that in my daily driver but, it's an option. It seems to have pretty good reviews.

 

[mrrsm]

With the Vehicle "Ice Cold"... Reach under the center area of the CAT S/S CAN.... and using a Dead Blow Hammer... Lightly Tap around on the Bottom area. Listen for the re-bound noise for what sounds like "Pocket Change being dropped into a Glass Bowl".

If you can hear that sound echoing inside... it's a sure sign that the Precious Metal impregnated Ceramic Honeycomb sections inside have Fractured and then Fallen to the Bottom of the Can. Besides having an out and out Clog... this condition will also obstruct the flow of the Exhaust Stream.

 

[budwich]

Based on the posted o2 response traces, it would appear that your cat is shot. :-( If the downstream sensor was "bad", it would be unlikely that it would be switching at any rate. Having said that, you need to provide more information about what the trace actually is.... is this at idle? If so what happens at 1500 rpm? Further, how long was the engine running before the trace was captured? You need to ensure a warm engine condition so that the sensors can be at "operating points". Next what software are you using to capture the info? Lastly, what is the history of the vehicle / engine? Just saying that you get good mileage doesn't really mean much. Posting fuel trim info that coincides with the traces will also provide useful information. Further on vehicle history, what is the status of your coolant?

 

[zaid3ssaf]

You could use an IR temp gun. Keep the engine revving at 2000 RPM and check the temps in and out of the cat. The out temp should be much higher than in temp as the cat burns the gases.

I think I've seen Eric's video before. I'll try to get my hands on a gun and see what happens

Sure but finding one that fits right might be difficult as the size is an oddball 2.75" instead of a standard 2" or 3". You might be able to weld in a 3".

I have bought a MagnaFlow cat for around $150 and I took it around shops to see if they would weld it on for me, but no one can. if you buy their universal cat its about $295. Do you think I can clamp a 2.5' on?

I'm about to dump a bottle of the CRC Guaranteed to Pass fluid into the tank to see if that "clears it up."

I'm going to do the same but with a gallon of lacquer thinner and then drive it for an hour or so.

With the Vehicle "Ice Cold"... Reach under the center area of the CAT S/S CAN.... and using a Dead Blow Hammer... Lightly Tap around on the Bottom area. Listen for the re-bound noise for what sounds like "Pocket Change being dropped into a Glass Bowl

I don't think the honeycomb is fractured. You'd hear rattling noise while driving, correct? Can I do that with a mallet?

is this at idle? If so what happens at 1500 rpm? Further, how long was the engine running before the trace was captured? You need to ensure a warm engine condition so that the sensors can be at "operating points". Next what software are you using to capture the info? Lastly, what is the history of the vehicle / engine? Just saying that you get good mileage doesn't really mean much. Posting fuel trim info that coincides with the traces will also provide useful information. Further on vehicle history, what is the status of your coolant?

Yes the picture is at idle. At 2500 RPM, the bands get closer, but they still follow the same trend. The engine was at temp and I was driving for about 30 minutes on the highway. Engine has 235,000 miles (I think it's the original), and coolant is brand new dexcool (I switched from regular recently). Software is car scanner pro, very good software. Here's the short term fuel trim after driving for 20 minutes.

 

[budwich]

OK... thanks for the extra info. Since you are getting down and dirty on this, the likelihood of having to replace the o2 sensor is high, you might try another test... how good are you at o2 sensor removal (I had some fun getting mine off... by heat and an Ice cold wrench provided enough thermal shock to remove it). You can try removing the downstream but leave it connected (ie. sitting in free space). Run the vehicle like this to see what the response is and whether it is different. Go from the result.

 

[mrrsm]

Yes... You can Test it With a Mallet...but much care has to be done NOT to Do More Harm Than Good... Unless you are certain that Fractured Honeycombs are not present and you want to skip this effort entirely... Perhaps you can slip a Chunk of Wood in between the CAT-CAN and the Mallet to prevent any excessive energy getting imparted within.

 

[Mooseman]

I have bought a MagnaFlow cat for around $150 and I took it around shops to see if they would weld it on for me, but no one can. if you buy their universal cat its about $295. Do you think I can clamp a 2.5' on?

Maybe. On my '02, I had used band clamps with a universal 3" cat. The original was in an awkward place but it held for quite some time until that one eventually failed. Then I just got one with the pipe. Much easier.

 

[zaid3ssaf]

UPDATE
Since we don't have smog or inspections in Iowa and my CAT is not clogged, I got me one of those eBay O2 extenders (basically a non-fouler) and mounted the downstream O2 sensor on it.

Before:

After:

M18x1.5

No P0420 code have come back yet.

 

[gmcman]

My cat will not light off at idle either, the downstream sensor mirrors the upstream. However at a cruise or slow city driving it will light off and the downstream sensor will turn flat.

It doesn't behave like this all the time, I generally get a mirrored waveform on the downstream but at a much lower intensity, more like a slight sawtooth waveform.

I'm sure it's needing replacement, but still hanging in there.

 

[JayArr]

I replaced mine with Walker version (Part#93253). I welded it in myself. I got my power back and the codes went away. The old cat that came out was about 95% clogged.

 

[zaid3ssaf]

I replaced mine with Walker version (Part#93253). I welded it in myself. I got my power back and the codes went away. The old cat that came out was about 95% clogged.

I wanted to do that. But shops wouldn't weld my new CAT for me and was quoted around $300 for a new one. so opted for doing this since I don't have any loss of power.

 

[JayArr]

I've often wondered if I could remove the cat completely and use an op-amp to duplicate the front O2 sensor except with a slight delay and at 1/3 or 1/4 the amplitude. I wonder if the computer would accept that and believe the cat was working.

I've got a lot of projects in my head for if/when I ever get to retire and spend all day every day in the garage. LOL

 

[Mooseman]

Easiest would be to use the spark plug defouler to pull the downstream O2 sensor out of the exhaust stream. Beyond that, deleting the sensor with a tune will do it (I can do that now!)

I've got a lot of projects in my head for if/when I ever get to retire and spend all day every day in the garage. LOL

That's what YOU think!

 

[Stugar]

Thanks, did this on mine this afternoon and fixed the P0420 code.

 

[JimInRadfordVA]

I had good luck with the "guaranteed to pass inspection" in a bottle on my daughter's Hyundai Tiburon. It was a 2005 with 210,000 miles on it. Followed the instructions and cleared up the problem in about 50 miles.

 

[Stugar]

Michigan doesn't have inspection, I just wanted the light to turn off. $6.99 and 20 minutes wasn't a lot of money or time, I think it was worth it.