Help! PO420 Catalyst System Efficiency Below Threshold

[LLC5]

Yes they are measuring Oxygen presence, but it is BASED ON TEMPERATURE. It's sort of like MEASURING horsepower. Horsepower is not measured, it is calculated based on torque and RPM to derive horsepower.

The Oxygen level is derived from the value from the Lambda Sensor which in automotive use is called an Oxygen sensor. It generates a Voltage that is determined by the temperature it senses. That is then used to DERIVE oxygen content.

It does NOT generate a voltage determined by the temperature that it senses, it generates a voltage based on oxygen content in the exhaust. High Oxygen content = low voltage (as low as .1v), low Oxygen content = high voltage (up to 1v). They are called "Oxygen Sensors", and not "Temperature Sensors", for a reason. No flame intended.

 

[TWISTERUP]

Well...... since catalytic converters weren't mandated in the US until model year 1975, I guess it would be difficult to test one on a 1973 car. To be such a genius, you're coming up short on information.

Now, just what in my previous post is incorrect? There are O2 sensors before and after the converters, and 100 degrees difference in and out is expected. So what is not correct?

I must point out that you continue to display your weakness and insecurity. You know, the building yourself up by putting others down?

And there you go again-- converters may not have been "mandated' (by the way I've got your "mandate") until 1975---but they appeared on American cars in 1973 right along with EGR valves ( I'm sure you know the theory of EGR--it works off washer fluid pressure generated by the washer pump) BTW if I'm wrong you need to contact the ASE about their EGR test question

It's clowns like you that give the the auto repair business a bad name--on this and other forums I hear the term "stealership" and it sorta ticks me off--'cause i work at one. In defense though of people who use that term they may have had work done by you or one of your brothers in stupidity.
That would leave a crap taste in any ones mouth !! I've known many like you always able to spout theory (I don't have a clue where yours came from) and in the real world-- couldn't change a flat tire. BTW you've got me pegged on one of your brilliant points--you can call me Mr."weakness and insecurity----now here's an area where you can call me Mr.Strong and Secure---drum roll please---that area is O2 sensor operation You keep 'em coming Mr. MGDiagMan 'cause I'm feeling more weak and insecure everytime you post

 

[MBDiagMan]

CLOWNS LIKE ME? Still building yourself up by putting others down? There are weak people like yourself everywhere. RANT ON PIPSQUEAK!!!!!!!!!!!

 

[Patrick]

You keep 'em coming Mr. MGDiagMan 'cause I'm feeling more weak and insecure everytime you post

CLOWNS LIKE ME? Still building yourself up by putting others down? There are weak people like yourself everywhere. RANT ON PIPSQUEAK!!!!!!!!!!!

Gentlemen,
The personal attacks need to stop. It's obvious you have a difference of opinion here, but you need to find another way to discuss it without resorting to name calling.

-Patrick,
CAC Forums Moderator

 

[XLR8]

This has gone so far off base regarding the original poster's request for information.

What started as an intelligent discussion has turned into a childish display of name calling and one upmanship.

That type of behavior will not be tolerated here.

This thread is closed.
Jane Ann

 

[XLR8]

dogfish246, as promised I'm unlocking this thread. Thanks for the PM, it was appreciated.

There's been a wealth of troubleshooting suggestions and experience offered up here. I sincerely hope you can get your issue resolved soon without taking too big of a hit in the wallet.

Good luck!
Jane Ann

 

[Hib Halverson]

My $.02... if you don't have emissions testing.

- Gut the cats
- Run with O2 simulators
- Swap and test the O2 sensors - replace if required
- Drive it 'till the wheels fall off

The original poster lists NJ as home and I'm pretty sure NJ has an exhaust emissions testing program and it might even incorporate an IM240-style test as do the areas in CA which require an "enhanced" test. If that's the case, the owner may want to carefully consider the above.

Earlier there was discussion about "moving" the sensors to see if the code moves or stays but then, "LLC5" reminded us all that there are other codes which set if there is a sensor problem.

In reviewing P0420 in the MY96 FSM, the solution to this is fairly simple but, unfortunately expensive in most cases.

I believe "dogfish 246" already established that no other DTCs are set but P0420, so if the cat is not an OE unit, if it's damaged or if it rattles (ie the substrate is loose inside) replace the cat.

If none of those problems exist, check to make sure both O2Ses on that side are properly installed and connected. If you didn't find a problem with the O2S wires, then replace the cat. If you find a problem with sensor wiring or connectors, repair them, clear codes and road test. If the DTC resets, change the cat.

Clear codes and road test.

Good luck.

 

[dogfish246]

The original poster lists NJ as home and I'm pretty sure NJ has an exhaust emissions testing program and it might even incorporate an IM240-style test as do the areas in CA which require an "enhanced" test. If that's the case, the owner may want to carefully consider the above.

Earlier there was discussion about "moving" the sensors to see if the code moves or stays but then, "LLC5" reminded us all that there are other codes which set if there is a sensor problem.

In reviewing P0420 in the MY96 FSM, the solution to this is fairly simple but, unfortunately expensive in most cases.

I believe "dogfish 246" already established that no other DTCs are set but P0420, so if the cat is not an OE unit, if it's damaged or if it rattles (ie the substrate is loose inside) replace the cat.

If none of those problems exist, check to make sure both O2Ses on that side are properly installed and connected. If you didn't find a problem with the O2S wires, then replace the cat. If you find a problem with sensor wiring or connectors, repair them, clear codes and road test. If the DTC resets, change the cat.

Clear codes and road test.

Good luck.

Yeah, I have to find out what the last year is for being exepmt for testing the exhaust. Its funny becasue I can delete the problem code and it wont come up for a few months. I had it in January, and deleted it and it just came back up a few days ago. Then a weed later it came up again and I deleted it. Now a few weeks later it has not come up???

I thought when cats go, they just go? Maybe I will check the wires to the o2 sensors. Also, can the sensors get dirty? Maybe if I take them out and use a compressor to blast air at it or something?

Thanks!:cool

 

[LLC5]

Yeah, I have to find out what the last year is for being exepmt for testing the exhaust. Its funny becasue I can delete the problem code and it wont come up for a few months. I had it in January, and deleted it and it just came back up a few days ago. Then a weed later it came up again and I deleted it. Now a few weeks later it has not come up???

I thought when cats go, they just go? Maybe I will check the wires to the o2 sensors. Also, can the sensors get dirty? Maybe if I take them out and use a compressor to blast air at it or something?

Thanks!:cool

More than likely the substrate in the catalytic converter is contaminated and it is not always at peak effeciency, which will intermittently set the code. Also, OBD 2 does not always set a code immediatley after detecting a problem (unless it is catastrophic to emission related equipment), so it may take a couple of drive cycles to turn on your engine light. Sensors can get dirty and go bad internally, but that would set other OBD 2 codes. PO420 means that the seconday (rear) O2 sensor is cycling voltage almost as fast (or as fast) as the primary (front) sensor and that the cat is not doing it's job correctly.

 

[dogfish246]

OK, would there be any tell tale signs that it is the cat converter? I dont smell sulfer, and the light has not come on for a while now.

I would hate to replace a cat! But if I did, do you replace both at the same time, or only the broken one? Is there anything tricky about changing a cat?

Thanks for all of the help!

 

[vdogamr]

I had to have my Cat replaced on my 88 shortly after buying it. I had one symptom: No power. I couldn't make it up a hill or achive more than 40mph on a flat surface. Had it towed to the mechanic. Now this was because my Cat clogged my entire exahust system. I was told by my mechanic that all 3 cats needed to be replaced and they had thrown chunks into the muffler. I put on a whole new Flowmaster exhaust system (only one Cat ) for much money.

When my CRV needed its Cat replaced it also had a noticable loss of power, but not undrivable. The tow truck guy gave me this quick and easy test (probably not fool proof): In neutral, give the engine a quick high rev and have someone else feel for a lot of exhaust gas comming out. If not then your exhaust system is probably clogged, ie your Cat is probably bad. Again I could not drive my car so your situation is different.

I doubt this all helps as much as I hope it will. But it may be helpful to know that a Cat is about $550 +- $100. It was for both cars. Even though in the end I think my new exhaust system was $1800+install.

 

[LLC5]

OK, would there be any tell tale signs that it is the cat converter? I dont smell sulfer, and the light has not come on for a while now.

I would hate to replace a cat! But if I did, do you replace both at the same time, or only the broken one? Is there anything tricky about changing a cat?

Thanks for all of the help!

The only signs of a low effeciency cat are a check engine light on OBD 2, or a less than 100 degree F difference between the inlet of the cat and the outlet, which is how you checked an OBD 1 or earlier system (OBD 1 had no secondary O2 sensor to monitor the cat). Other signs of a bad cat are noises (buzzing, jingling, etc) or poor performance when they physically fall apart internally, but low effeciency is not detected visually unless it is combined with physical damage. You only need to replace the one cat as the other one is on a different bank of cylinders. There is nothing tricky about replacing one, they are usually bolted on, but some do require welding.

 

[dogfish246]

Thanks Everyone!

I guess I will wait for the check engine light to come back on since the Vette is performing beautifully right now! Then I will replace the cat!

 

[LLC5]

Thanks Everyone!

I guess I will wait for the check engine light to come back on since the Vette is performing beautifully right now! Then I will replace the cat!

As a side note, if you do replace the cat be aware that a-mkt cats are generally not as effecient as OEM units and can set codes, especially high flow cats. Also, cats can be damaged by cylinder misfires, coolant from bad head gaskets, and incorrect A/F ratios, so make sure your vehicle is operating properly before replacing an expensive converter. I am not saying that your vehicle has any of these problems as usually other OBD 2 codes would be set, just to be aware of them. If you do buy an a-mkt cat, as they are usually a lot less money than OEM, shop around and make sure it comes with a strong warranty. Good luck with it.

 

[dogfish246]

As a side note, if you do replace the cat be aware that a-mkt cats are generally not as effecient as OEM units and can set codes, especially high flow cats. Also, cats can be damaged by cylinder misfires, coolant from bad head gaskets, and incorrect A/F ratios, so make sure your vehicle is operating properly before replacing an expensive converter. I am not saying that your vehicle has any of these problems as usually other OBD 2 codes would be set, just to be aware of them. If you do buy an a-mkt cat, as they are usually a lot less money than OEM, shop around and make sure it comes with a strong warranty. Good luck with it.

Thanks, that is good advice! Just the advice im looking for!

 

[Remo]

Rear 02 Sensors

The rear 02 sensors throwing codes is a common problem especially with the C5 guys who have installed long tube headers with high flow cats. The most popular resolution is to get the car retuned and intall a set of 02 simulators on the rear sensors.
Remo:cool

O2 Simulator & Tester - LT1 LS1 V6 Camaro Firebird Corvette

 

[Hib Halverson]

"LLC5's" posts two aboove this one is very important information about cat issues.

As for the one by "Remo" above, I think all it does is confuse the issue, but I'll be a "nice" guy and ask "Remo" how does that apply to an LT1 with no headers and stock cats which has to pass an IM240 exhaust emissions test?

 

[Remo]

"LLC5's" posts two aboove this one is very important information about cat issues.

As for the one by "Remo" above, I think all it does is confuse the issue, but I'll be a "nice" guy and ask "Remo" how does that apply to an LT1 with no headers and stock cats which has to pass an IM240 exhaust emissions test?

Good point Hib.....I'll step out.
Remo

 

[dogfish246]

No, that was helpful. Maybe I will check out this path too. If I ever get headers and a new exhaust without cats, this is another path to check out. Then I could use an O2 simulator... But then I would have to find someone to get my car "inspected"!

Probably will just get a new cat when the time comes, but all insight is welcome, as long as it is friendly!:cool

Thanks Guys!

 

[Hib Halverson]

Good point Hib.....I'll step out.
Remo

No...
:ugh
Don't "step out".

Let's all try and help the ole "dogfish" with his particular problem.

As for the part about headers...if you go that route, what Remo says becomes pertinent, however, before you put on headers make sure whatever emissions test you have in NJ cause problems for a car with headers.

In fact, if there is a state exhaust emissions test in Jersey, I'd be interested to know how it works.