Catalytic Converter Test/Replace?

[MadNad]

I have a good feeling ( or bad as it may be ) that my catalytic converter needs replacing. The reasons I believe it needs replacing are that I barely passed HC on emissions recently and am getting a bit less gas mileage than I think i should be ( around 250-275 / tank ). The exhaust also smells a bit more than I think it should. I also believe I am burning some oil which I heard can contaminate the cat with phosphorous and shorten its lifespan.

I recently replaced a HG (all gaskets), timing belt, spark plugs/wires, o2 sensor (bosch), installed Apexi air filter, coolant/vacuum hoses. Is there way to test the cat ( yes I'm in CA )?

Finally, if I do replace, do you have any suggestions for what I should get(i have stock exhaust)? Can anyone recommend a catalytic converter for a CA registered supra? The toyota ones seem to be 4x the price of after market ones. Anyone try CATCO, BOSAL, or WALKER cats?

 

[RockPaperSwoRD]

a cat only DECreases gas mileage, its not some magic box that improves fuel economy. its just a filter for your emissions. being in cali, you do need a cat so i would get a hi flow 3 inch and go catback for the rest

 

[MadNad]

a cat only DECreases gas mileage, its not some magic box that improves fuel economy. its just a filter for your emissions. being in cali, you do need a cat so i would get a hi flow 3 inch and go catback for the rest

Thanks RockPaperSwoRD, my understanding was that one of the symptoms of an clogged/blocked cat was a drop in fuel economy due to excessive backpressure.

Regardless, I do need a cat, and I was hoping someone out there might have some experience dealing with them for a CA registered car.

 

[suprarx7nut]

What parts of Smog did you do worst in? I think high Nox can be a sign the cat is about toast. :dunno: Though I'm sure a non-working cat would have negative effects on most gases.

 

[xarewhyayen]

I have a good feeling ( or bad as it may be ) that my catalytic converter needs replacing. The reasons I believe it needs replacing are that I barely passed HC on emissions recently and am getting a bit less gas mileage than I think i should be ( around 250-275 / tank ). The exhaust also smells a bit more than I think it should. I also believe I am burning some oil which I heard can contaminate the cat with phosphorous and shorten its lifespan.

I recently replaced a HG (all gaskets), timing belt, spark plugs/wires, o2 sensor (bosch), installed Apexi air filter, coolant/vacuum hoses. Is there way to test the cat ( yes I'm in CA )?

Finally, if I do replace, do you have any suggestions for what I should get(i have stock exhaust)? Can anyone recommend a catalytic converter for a CA registered supra? The toyota ones seem to be 4x the price of after market ones. Anyone try CATCO, BOSAL, or WALKER cats?

If youre burning oil you will be high on HC's. Oil has alot of hydrocarbons in it. Newer oils have very low amounts of phosphorous now. I wouldnt point straight at a cat, i would try to figure out why you're burning oil and focus on that.

What parts of Smog did you do worst in? I think high Nox can be a sign the cat is about toast. :dunno: Though I'm sure a non-working cat would have negative effects on most gases.

Modern cats reduce Nox, Using a 3way cat. platinum and palladium help to convert hc and co. Rhodium is added to reduce oxides of nitrogen. Failing for nox would be more likely an issue of running hot, incorrect timing, Excessive compression due to carbon build up etc.

IIRC our cats don't employ rhodium. I THINK they're 2 way cats not three way, but someone please correct me if i'm wrong

I wouldn't jump towards blaming a cat for "almost failing" hc, id blame the fact you claim you're burning oil at this point.

 

[Poodles]

Our cars run rich naturally, it's a conservative tune that is more safe than it is efficent.

That being said, how much oil do you burn?

 

[suprarx7nut]

Modern cats reduce Nox, Using a 3way cat. platinum and palladium help to convert hc and co. Rhodium is added to reduce oxides of nitrogen. Failing for nox would be more likely an issue of running hot, incorrect timing, Excessive compression due to carbon build up etc.

::dunce:: I just realized I confused/mixed the function of cat with the function of egr systems. I will now be a spectator to this thread.

 

[Poodles]

Yep...

But the fact is it's all a mute point until we know his mods and see the inspection results.

A worn out cat will usually fail for HC's in my experience. The first time I had my car inspected it barely passed. The second time it failed...barely. Replaced the cat with a high flow metal core cat and it went WAY down.

Same thing on other vehicles I've owned and worked on.

 

[jetjock]

So oil contains a lot of hydrocarbons eh?

1) Our cars use 3-way catalysts.

2) Our cars don't run rich, at least not where the cat and emissions testing are concerned.

3) A new cat will mask feed gas problems. The state will be happy but that doesn't mean the engine will be.

4) People who ask for emissions help should post test results.

5) Other BS in the thread isn't worth correcting...

 

[MadNad]

These are the hyrdrocarbon levels on the last emission test I did. Everything else was way under.

MAX | AVE | MEAS
124   41    95       @ 15mph
99    29    74       @ 25mph

An Apexi air filter is the only mod i have. The car has always burned oil (since before I got it 12 yrs ago), but not always done so poorly on emissions. Looking at my records, the results went from great emissions to, two years later, very poor HC emissions. I am embarrased to say that I haven't done a compression test but I am almost certain I am burning oil thru the rings (having rebuilt the head on the BHG).

What I was hoping to find out was a good method for testing if a cat has failed, and/or suggestions for what brand to replace it with if/when I do need to get a new one.

 

[jetjock]

Best to always post all the numbers up. It's called gas analysis for a reason.

Techs have been searching years for a definitive efficiency test but aside from using a gas analyzer before and after the cat nobody has been able to come up with one. Pity you aren't closer or I'd help since I currently own 5 of the things. About all you can do is check temps at the cat's inlet, center, and outlet. Look for at least a 100 F increase from front to back. An infrared temp gun is good for that. Just be sure the cat is lit off. If there's not much change in temp across the cat the odds are it's dying.

 

[xarewhyayen]

So oil contains a lot of hydrocarbons eh?

1) Our cars use 3-way catalysts.

Thank you for verifying that, i wasn't sure. I didnt know if they were used that early. does oil not contain hydrocarbons?

 

[jetjock]

Three ways were in use well before the MKIII came along and yeah, oil contains some percentage of hydrocarbons

 

[xarewhyayen]

Three ways were in use well before the MKIII came along and yeah, oil contains some percentage of hydrocarbons

Well thank you for correcting me :thumbup: Good to know.