If your converter were below threshold, you should get a CEL. If not, at least you should have a rotting egg smell.
Catalytic Converter
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I have a couple of cheap suggestions to try FIRST before expensive options...
First try using a bottle of Techron Fuel System Concentrate cleaner...Add the bottle to your tank when almost empty and only fill with about 7-8 gallons of fuel..
Make sure to take the car out on some prolonged high speed drives (high RPMs) at least as long as an hour at a time. It is important to get the catalytic converter temp up to a good operating temp for a long period of time at least an hour..Perhaps you have contamination on the substrate inside Or build up of coolant silicates which might clog it a bit.
Also check your oil level..is it above the fill mark quite a bit...if so oil is travelling into the converter and contaminating it as well. Oil level should NEVER be above the full line on the dip stick. If the oil hasn't been changed in a year or 6000 miles change it and make sure NOT to over fill.
I get the feeling that the unit is not melted inside but instead there is build up on the substrate making it less efficient and blocking SOME flow.
I have a couple of cheap suggestions to try FIRST before expensive options...
First try using a bottle of Techron Fuel System Concentrate cleaner...Add the bottle to your tank when almost empty and only fill with about 7-8 gallons of fuel..
Make sure to take the car out on some prolonged high speed drives (high RPMs) at least as long as an hour at a time. It is important to get the catalytic converter temp up to a good operating temp for a long period of time at least an hour..Perhaps you have contamination on the substrate inside Or build up of coolant silicates which might clog it a bit.
Also check your oil level..is it above the fill mark quite a bit...if so oil is travelling into the converter and contaminating it as well. Oil level should NEVER be above the full line on the dip stick. If the oil hasn't been changed in a year or 6000 miles change it and make sure NOT to over fill.
I get the feeling that the unit is not melted inside but instead there is build up on the substrate making it less efficient and blocking SOME flow.
Originally Posted By: exranger06
Removimg the cat is a federal crime and is illegal in all 50 states. Doesn't matter if your state has emissions testing or not. $1300 is ridiculous, get it fixed (properly) somewhere else.
X2. Check with local muffler shops. I reciently had a customer come in wanting 3 cats for his Suzuki whatever it was. He had an estimate from the dealer for $7k.
Removimg the cat is a federal crime and is illegal in all 50 states. Doesn't matter if your state has emissions testing or not. $1300 is ridiculous, get it fixed (properly) somewhere else.
X2. Check with local muffler shops. I reciently had a customer come in wanting 3 cats for his Suzuki whatever it was. He had an estimate from the dealer for $7k.
JHZR2
Staff member
Originally Posted By: MrRPM
look into aftermarket CATs that are often advertised as high flow. they are usually pretty cheap compared to an OE replacement and should keep your O2 happy.
They start at such low conversion that they are no better than an end of life OE converter when new. Been there done that.
look into aftermarket CATs that are often advertised as high flow. they are usually pretty cheap compared to an OE replacement and should keep your O2 happy.
They start at such low conversion that they are no better than an end of life OE converter when new. Been there done that.
The cat went bad on my Civic, it kept throwing the code, and fuel mileage was down. I cut out the old cat, and welded in a piece of pipe. Added an '02 bung to the pipe, and did the old spark plug anti fouler trick, and inserted O2 sensor.
Car runs great, and no more CEL. Hey, I'm a real rebel!
Car runs great, and no more CEL. Hey, I'm a real rebel!
Originally Posted By: exranger06
Removimg the cat is a federal crime and is illegal in all 50 states. Doesn't matter if your state has emissions testing or not. $1300 is ridiculous, get it fixed (properly) somewhere else.
If a tree falls in a forest and no one is around to hear it, does it make a sound?
Removimg the cat is a federal crime and is illegal in all 50 states. Doesn't matter if your state has emissions testing or not. $1300 is ridiculous, get it fixed (properly) somewhere else.
If a tree falls in a forest and no one is around to hear it, does it make a sound?
Propflux01
$100 Site Donor 2026
There was a YouTube video on here somewhere that described how to clean out a cat, maybe try that before you remove it?
Originally Posted By: Tim H.
There was a YouTube video on here somewhere that described how to clean out a cat, maybe try that before you remove it?
Be careful Tim and others here suggesting that emissions devices be defeated.
I believe that advocating this is against the forum rules and you could be banned for it. just saying.
There was a YouTube video on here somewhere that described how to clean out a cat, maybe try that before you remove it?
Be careful Tim and others here suggesting that emissions devices be defeated.
I believe that advocating this is against the forum rules and you could be banned for it. just saying.
i have read about a way around the trouble. i have not used it so i cant say it will work. let the fuel go down to 1/4 tank. then add 6-7 gal of methanol to the tank. it will run bad but it might pass the test. after the test is over add more gasoline. like i say i dont know it will work. or you might get in trouble, for not using gas.
Originally Posted By: 91344George
Originally Posted By: Tim H.
There was a YouTube video on here somewhere that described how to clean out a cat, maybe try that before you remove it?
Be careful Tim and others here suggesting that emissions devices be defeated.
I believe that advocating this is against the forum rules and you could be banned for it. just saying.
Believe he's talking about literally washing the honeycomb with "something" and bringing it back to life.
You don't need a youtube to describe gutting the thing.
Originally Posted By: Tim H.
There was a YouTube video on here somewhere that described how to clean out a cat, maybe try that before you remove it?
Be careful Tim and others here suggesting that emissions devices be defeated.
I believe that advocating this is against the forum rules and you could be banned for it. just saying.
Believe he's talking about literally washing the honeycomb with "something" and bringing it back to life.
You don't need a youtube to describe gutting the thing.
Propflux01
$100 Site Donor 2026
Originally Posted By: eljefino
Believe he's talking about literally washing the honeycomb with "something" and bringing it back to life.
You don't need a youtube to describe gutting the thing.
Thank you for clarifying that.
Believe he's talking about literally washing the honeycomb with "something" and bringing it back to life.
You don't need a youtube to describe gutting the thing.
Thank you for clarifying that.
JTK
$100 Site Donor 2025
Originally Posted By: bdcardinal
Depending on which engine the Sable has and the location of the converter it could very easily be $1300. Some of those cars have a one piece Y-pipe with 2 or 3 cats on it. And since it is factory it is direct fit with no modifications.
Exactly what I was thinking.
It's a V6, so 2-3 cat's on a one-pc Y-pipe assembly. Real expensive regardless of OEM or aftermarket- if there's one even available.
I have a hard time believing these CCs have anything to do with your fuel economy concerns. If one or more were plugged, you'd have some serious running/performance issues.
If I had a downstream O2 sensor code on a 15yr/old Sable, or a plugged CC, I'd hollow out the cat and install an "anti-fouler" on that downstream O2 sensor and be done with it. No way I'd throw that kind of coin into the exhaust alone.
Depending on which engine the Sable has and the location of the converter it could very easily be $1300. Some of those cars have a one piece Y-pipe with 2 or 3 cats on it. And since it is factory it is direct fit with no modifications.
Exactly what I was thinking.
It's a V6, so 2-3 cat's on a one-pc Y-pipe assembly. Real expensive regardless of OEM or aftermarket- if there's one even available.
I have a hard time believing these CCs have anything to do with your fuel economy concerns. If one or more were plugged, you'd have some serious running/performance issues.
If I had a downstream O2 sensor code on a 15yr/old Sable, or a plugged CC, I'd hollow out the cat and install an "anti-fouler" on that downstream O2 sensor and be done with it. No way I'd throw that kind of coin into the exhaust alone.
I agree, JTK. I'm just looking for a quick fix. There is no rotten egg or gas smell after I finish driving, only a fuel mileage reduction of 5mpg... I check out Scotty Kilmer on youtube and he suggested adding a gallon of lacquer thinner to 7 gallons of gasoline and driving it for 120 miles. Anyone ever tried this? If the point is to get the converter hot in an attempt to clean out any blockage, should I fill up with high octane fuel?
Just saw an advertisement on youtube for a product called cataclean which is sold at Pep Boys. Anyone have experience with this?
From what I have heard here, the Cataclean does NOT work.
Once again, what makes you think that cleaning your catalytic converter is going to give you back the lost 5 mpg? I do not believe dirty converter is robbing you of the mileage.
If you are not getting P0420 (or P0430) code, then you are barking at the wrong tree. If you are getting those codes, that will NOT result in your mileage going down.
P0420/P0430 codes are extremely aggressive i.e. they turn on when the converter efficiency drops from 100% to 90%. To put it another way, even when you get those P0420/P0430 codes, there is nothing physically wrong with the car or emission, ASSUMING EVERYTHING ELSE IS WORKING CORRECTLY.
Now if you have been driving with those code for years, then all bets are off. But there are ways to find if your converter is plugged up. You use vacuum gauge and snap throttle test to diagnosis plugged exhaust system. If it is clogged, no cleaner in the world is going to fix it for you.
You need to approach this problem logically rather than throwing parts at it.
- Vikas
Once again, what makes you think that cleaning your catalytic converter is going to give you back the lost 5 mpg? I do not believe dirty converter is robbing you of the mileage.
If you are not getting P0420 (or P0430) code, then you are barking at the wrong tree. If you are getting those codes, that will NOT result in your mileage going down.
P0420/P0430 codes are extremely aggressive i.e. they turn on when the converter efficiency drops from 100% to 90%. To put it another way, even when you get those P0420/P0430 codes, there is nothing physically wrong with the car or emission, ASSUMING EVERYTHING ELSE IS WORKING CORRECTLY.
Now if you have been driving with those code for years, then all bets are off. But there are ways to find if your converter is plugged up. You use vacuum gauge and snap throttle test to diagnosis plugged exhaust system. If it is clogged, no cleaner in the world is going to fix it for you.
You need to approach this problem logically rather than throwing parts at it.
- Vikas
Vikas, thanks for the info. I'm somewhat confused because I know very little about exhaust systems. I took the car to an independent garage and they said I needed what as akin to a software update in my car's computer and that the dealership was the only place this could be done. I went to the dealership and they are telling me is a p4030 code. Now, my CEL has been on for about three years. I got the codes scanned at auto zone every now and then to see if anything changed. They couldn't give me an exact diagnosis, only to say it was either an issue with the CC, O2 sensors, or vacuum leak...... I assume a dedicated muffler shop would be able to run the vacuum gauge and snap throttle test?
The independent would have been right about updating the software. Remember how I said the CEL turning on when the efficiency drops from 100% to 90%? Some manufacturer can detune it so that the 90% number is changed to (say) 80%. However, they will only do that if the vehicle is still inside the EPA mandated emission warranty (8/80K).
An independent should be able to run the snap throttle test. Go back to him and ask to run it or you might be able to run it yourself if you can buy a vacuum gauge. They are not that expensive. I am assuming that since you are asking questions here, you are willing to try few options on your own before letting somebody else fleece you. If you trust your independent mechanic, ask him to find out if your converter is blocked by doing the snap-throttle test. I suspect he believe it is NOT.
Is it possible that your converter is completely clogged? I do not think so. What other symptoms are you having? Does the car feel like it is running out of steam? Is it hard to rev the engine? After a highway drive during the night, open the hood and also peek under the car. Do you see glowing exhaust or catalytic converter? There can be lots and lots of things which could cause the mileage to go down. Some of the previous contributors have already listed them. For example, dragging brakes could easily drop the mileage. It is also easy to find. After the drive, just compare the temperature of all wheels (just be careful and don't burn your fingers!). If you find a hot one, you know you have a stuck caliper. If the car does not roll easily in neutral, then that would be it. A scanner can tell you if your fuel trims are at the end of the acceptable level. MAF reading can tell you if you have vacuum leaks or dirty or bad MAF. A cheap and competent scanner costs under $100 and can give you a view inside your engine's health.
I have been driving all my vehicles now for many years with the P0430/P0420 code disabled and to the best of my knowledge, no harm has been done so far.
In the end, it all depends upon the strength of your own determination to diagnosis this situation. There are very few mechanics who are smart and patient enough to spend the necessary time with your vehicle in the limited span of time that they have. You on the other hand are living with that vehicle and have all the time. You also can notice abnormality with the vehicle given its history. If inclined, you can invest some money in the tools and get your hands dirty.
Is the independent mechanic your usual mechanic? If you do not want to get dirty, stick with him and work with him. That is what I do even though I own more tools than he does
Best of luck!
- Vikas
An independent should be able to run the snap throttle test. Go back to him and ask to run it or you might be able to run it yourself if you can buy a vacuum gauge. They are not that expensive. I am assuming that since you are asking questions here, you are willing to try few options on your own before letting somebody else fleece you. If you trust your independent mechanic, ask him to find out if your converter is blocked by doing the snap-throttle test. I suspect he believe it is NOT.
Is it possible that your converter is completely clogged? I do not think so. What other symptoms are you having? Does the car feel like it is running out of steam? Is it hard to rev the engine? After a highway drive during the night, open the hood and also peek under the car. Do you see glowing exhaust or catalytic converter? There can be lots and lots of things which could cause the mileage to go down. Some of the previous contributors have already listed them. For example, dragging brakes could easily drop the mileage. It is also easy to find. After the drive, just compare the temperature of all wheels (just be careful and don't burn your fingers!). If you find a hot one, you know you have a stuck caliper. If the car does not roll easily in neutral, then that would be it. A scanner can tell you if your fuel trims are at the end of the acceptable level. MAF reading can tell you if you have vacuum leaks or dirty or bad MAF. A cheap and competent scanner costs under $100 and can give you a view inside your engine's health.
I have been driving all my vehicles now for many years with the P0430/P0420 code disabled and to the best of my knowledge, no harm has been done so far.
In the end, it all depends upon the strength of your own determination to diagnosis this situation. There are very few mechanics who are smart and patient enough to spend the necessary time with your vehicle in the limited span of time that they have. You on the other hand are living with that vehicle and have all the time. You also can notice abnormality with the vehicle given its history. If inclined, you can invest some money in the tools and get your hands dirty.
Is the independent mechanic your usual mechanic? If you do not want to get dirty, stick with him and work with him. That is what I do even though I own more tools than he does
Best of luck!
- Vikas
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