Do cat cleaners work?

[Bonnewagon]

I saved a complete exhaust system from a '95 Sunfire parts car to use on my '99 because it was practically new, not even rusty. So I finally had to use it and I welded it up and all seemed well until weeks later I got the dreaded P0420 code for "inefficient catalytic converter operation". That surprised me as the cat looked perfect and there are no exhaust leaks. The old system was 15 years old and the flex pipe leaked yet it never set a code. Stupidly I tossed the old rusty cat. The other thing was that I saved the downstream O2 sensor figuring it worked so why change it. The only thing I can suspect is that the parts car had suffered an engine failure, though not mechanical, and maybe it dirtied the cat. So I want to try a cat cleaner before I go replacing any more parts. Has anyone tried these and did they work? If so what brand? I have seen that code pop up on two of our Jeeps and an oil/air filter change cured it, but not on this Sunfire.

 

[pontiacgp]

Mark, I have never heard of cat cleaners (except for pet soap) so you got my interest. I'm not a fan mr gasket but that brand seems to be an online favorite when it comes to cat cleaners.

 

[mac61891]

I would seriously doubt that a Cat Cleaner would work. Likely cause for your code, is that the pre OBDII was not compatible with the OBDII model. They may look alike, but the newer would have had a tighter tolerance. Second, if the replacement was actually an aftermarket, it is very common on GM's to have that code. I operate a repair shop and I will never put an aftermarket cat on a GM. The aftermarkets just do not work well enough on GM to keep the lights out.

 

[Bonnewagon]

Mac61891- I thought that also, but it was a Walker model, with a bung for the downstream O2 sensor and the whole shebang was complete from the engine flange to the resonator flange. I can only find that type assembly available for the '96 to '99, so it covers OBD-2. The '95 is a cat only that must be welded in. The car I took it off had no O2 sensor in place, but I figured either they didn't care about passing the emissions test, or that part of CT was lax, or it was as you said, an OBD1 car. But the cat pipe was intended for OBD2, just maybe not NY or Cali. So what you are saying is that I screwed myself tossing the GM original- that figures.

 

[pencero]

Walker is cheap. You get what you pay for. My Walker exhaust worked perfectly fine and sounded good but got surface rust in only a few weeks of being on the car. Try clearing the code right before going for plates. You should be able to get through w/ your fingers crossed and the light will hopefully not turn back on until you're safely on the way home. Consider the problem from outside the box too; a pollution control device on the engine could be causing the code too so dont rule that out before doing all that extra work putting a rusty old gm cat on there again... On a Honda here a similar code recently went away after the weld just before the cat was redone. The fumes escaping at this weld will set off the o2 sensor easily even though its sealed in that cat a cheap brand offers less insulation. Either way it goes expect short life and surface rust if you keep this exhaust. I got my 2 winters out of mine and moved on to a different exhaust soon as I could afford something better.

 

[Bonnewagon]

I plugged in my OTC scanner and watched the O2 values as the car ran. The upstream O2 was fluctuating wildly, as it should, but the downstream sensor was pretty erratic too. It should stay pretty steady if the cat was doing it's job, and the sensor not damaged. I ordered a replacement sensor just because it was 15 years old and I had a hard time getting it off the old pipe and on to the new one. I put the cleaner in and drove it and I will change the sensor if it still doesn't clear up. If after all that it still acts up I guess I will need a new cat. EDIT- I see 49 state, and 50 state types. So is a cat that is legal for use in California, as good as a GM original?

 

[pontiacgp]

Mark, have you checked the temperatures on the cat?. It should be around 100 degrees hotter at the outlet than the temperature at the inlet if it's working right

 

[mac61891]

The walker is likely the issue. Aftermarket on OBDII Gm's just do not work. I do agree with GP, the temp could be an issue as to why the aftermarkets don't work.

 

[mebe007]

Mark not sure what kind of visual inspection you have to pass up there but here in virginia you just have yo have the right equipment. I removed the precast on my 03 s10 and installed a MagnaFlow high flow in place of my factory cat. I was throwing the code for the cat. What I did was take 2 spark plug antifowlers and drI'll the first one out and thread the O2 sensor in, then thread that into the next undrilled antifowler and install into the pipe post cat. It senses the heat and thinks all is good but doesn't sniff much so no light. Looks pretty incognito as well

 

[Bonnewagon]

Thank's Mark, that's what my mechanic shop buddy suggested also. It'll work for sure. My only question was if the O2 was same threads as a spark plug, looks like it is by your pic. Steve/Mac, you're probably right, not hot enough to burn it all up. GM WholesaleDirect lists the cat/head pipe at $1,160.91, discounted from list of $1289.90. Wowsers!!! And it's only 49 state legal. I only paid 2G for the whole car! Still kicking myself for tossing the old one- live and learn.....