I got a P0420 code on my older GM car, and did try putting in a new downstream O2 sensor, first... but the code came back. It was indeed the catalytic converter.

For the record, I have the original O2 sensor in my 27 year old (GM) work truck. I do not have the original catalytic converter in that truck, I replaced it with an eBay cat (Canadian Company). In addition to getting a P0420 on the truck, the cat also "rattled" when I decelerated. Have you heard any "rattle" type of sounds when decelerating??

I did have a friend who purchased a used car and the used car dealer welded in a used cat -- just so the car wouldn't throw a P0420 code. That used cat lasted about a year. Is it possible that the seller put in a junkyard or used cat into the car. I find it odd that a cat (even a cheaper cat) would go bad in a year (unless the cat got polluted by oil or too rich a mixture).

Maybe... When Tony is installing the catalytic converter, have him check if the car is running rich??

I'd hate for you to spend all of this money installing a new cat, only to have it polluted and destroyed by an underlying problem.

 

That was my concern, too, replace it and it gets ruined. That fuel mix was my question for the highly rated muffler shop, and he said if it wasn't right the O2 would throw a code. I thought the exhaust fumes would reveal a too-rich fuel mix. How does one detect too-rich fuel? Seems like I can smell a very slight odor of fuel in the cabin. I'm tempted to buy a deep socket, find that O2 under the hood, remove it and clean it.

 

You can purchase a special O2 sensor removal tool. It looks like a socket with one of the sides cut out. Personally, I use an open end wrench. The downstream O2 sensor is more likely to throw a P0420 code. A bad upstream O2 could make your mixture too rich, that might also explain the fuel smell you are detecting.

Just my opinion here, but if I go through the trouble of pulling something (like an O2 sensor), I replace it -- but that is just my opinion. I'm starting to get old and my back doesn't like doing jobs twice.

Ask Tony if he owns a 5 gas Analyzer. I don't 100% trust the fuel trims, but if he doesn't have one of those, see what the short and long term fuel trims are. If you want to educate yourself about fuel trims there is a great two part youtube video (Shrodingers Box)

If you think you are smelling raw gas or a rich mixture that condition would pollute the new cat that the previous owner put on. And if that issue still exists, you are going to do the same thing to the new cat -- you are putting on.

It is definitely worth further investigation.

 

Thanks, I've been pondering this and thinking I need to find a good mechanic to do what you said. At least now I know the right question. I mentioned the smell to the muffler man, and he did not have an intelligent answer like you did.

 

You stated the car does not burn oil and if the previous owner put a new cat on the car prior to the sale; something polluted that cat. A new cat can handle a rich mixture for a little while, but the rare metals in it get used up quickly. At that point, the cat can no longer process the extra fuel/hydro carbons and it fails (P0420). Logically, this would make sense since you stated you are smelling something. If its really rich, it might even cause your eyes to water, a bit.

For the record, I'm a "shade tree" mechanic and never did it as a profession. I just work on my own vehicles and a few friends' cars/trucks.

 

There is a definite difference in raw gas smell and that from a cat at rich. The cat produces a lot of sulfur oxides and the smell is not the same.

 

If the catalytic converter is bad/dead, unburned hydrocarbons (getting past the catalytic conversion process) will have the odor of gasoline.

The one shop already stated the catalytic converter is bad, so its not doing its job, thus unburned hydrocarbons will continue through the cat and out the tail pipe.

I was going to suggest the owner stand behind the car (while its running) and try to focus on the smell, but since the other shop stated the cat was bad, there was no reason to put him through that.

If the cat was still good and the mixture was rich, then you'd get that "sulfur" or "rotten egg" smell but the cat isn't doing its job, thus the car threw a P0420 code.

 

All correct. The rotten egg smell is the sulfur and it shows the cat at that time is working furiously to convert but that much rich commonly smothers the cells to then kill the cat quick. You can kill one in 10 minutes if flooded enough, then the cat quits reducing and you get the raw gas smell because it is dead.

 

Took it to highly rated (4.9) shop and asked if they could figure out why the cat went bad in a year. Said they could. I don't think they did. They said they need to replace it first and the two O2 sensors and go from there at a cost of around $1760. They never sufficiently said what caused it other than it's probably a cheapo, and others said even a cheapie should last longer. Nissan dealer wanted around $2700. I think it's vacuum or fuel trim after watching most of Schrodengers Box. Called previous owner, my neighbor, and he said a shop did it just before I bought it in May '24. He said he's going to see if the shop will warranty it. I have a supposedly good one with warranty from E-Bay for $67. I'll do one a year for $300 with labor with Tony the Tiger before I have these guys do it. The muffler shop wanted $850 and two year warranty. He said he knows nothing about the O2 sensor necessity; would put em on if I want. He doesn't recommend one way or the other.

 

Did that shop (the 4.9 rated one) have a 5 gas analyzer?? It is an expensive piece of equipment, not all shops invest in them. I'd want to know what is coming out of the tailpipe, before installing the new cat.

I still think something is wrong and the mixture is too rich. What kind of gas mileage is the car getting?? Highway?? City?? Just curious...

 

MPG is around 22 around town. That's a clue. I forgot to ask about the 5 gas analyzer, wrongly assumed they knew their stuff, but I just now called em back today and asked - They don't. Again, their experience is aftermarkets don't last long. I asked who does have one; he said probably the dealer (aka stealer). The former owner, my neighbor, is gonna call the shop that installed it last year, and check on the warranty. He paid $1500 for it! I said to act like you still own it. He said he'd call today. Fairway Auto, the shop, said they checked temp and found it cold on the outlet, so it's clogged. Duh, we know that already. WHY? is the question no one can answer, and it's coz the computer is not telling them IMO. If clogged would it get a good read on the exhaust? The mechanics out there are not as privy as the guys on YouTube, or even a half-smart shade tree . When I left the car overnight on Wed., I asked in a note to additionally check if ground to starter was good; coz 10% of the time it doesn't kick in right away. When I picked it up at closing time yesterday, they said they didn't check that. They recommended other things in need: coolant flush (I did that last year); rear shocks leak R & R $1,035 ; and valve cover gasket leak (probably where the fumes originate) $784 for gasket . Spark plugs R7R $479. It was like a visit to Jiffy Lube! I'd rate 'em at 2 stars! They're crazy. I used them years ago, and they weren't this way. Progress! I'm about ready to let Tony do the cheapy delivered yesterday from China, or the muffler shop do it for $850 w/ 2 yr; 25K mi. warranty; get the ground on the starter cleaned so it'll start 100% of the time rather than 85%, and let a new owner worry about what falls off next. Then shop for a well-maintained, -documented older Honda or Toyota. If I do fix the other stuff, it's Tony time. His shop is about ten mi. away in a different county, a less urbanized area, putting it politely. Actually looks like a scene out of Deliverance . His building, shop, and lot may not be cleanest, but his way of doing business is cleaner than than most I've found. I may even have him install this Chinese-made, e-bay cat that got delivered yesterday. Thanks for all your help. I appreciate it greatly.

 

22 MPG?? That sounds pretty low. I'm getting 40 mpg (city/highway combined). Yes, my money is on a rich mixture killing the cat. The 5 gas analyzer would tell you (definitely) why the previous cat gave up after a year.

As far as Honda(s), I had two of them that went well over 250K miles with no major problems, try to find a manual transmission. I also had good luck with GM products, again manual transmission vehicles. My work truck is 27 years old -- no real major repairs.

As far as automatic transmissions, my girlfriend's Dodge (non-cvt) is actually doing pretty good. A few nuisance repairs, but other than that it has been a really solid car. It is very easy to work on. I keep up with the maintenance on it, as well. I did have to paint it last year as the desert sun killed the clear coat, but I can't really blame Dodge for that.

If you have to get an automatic transmission, look for a non-cvt and no DCT transmissions, if you can help it.

Just my two cents.

 

If fuel is rich, how is it normalized?

 

Everything working right the computer tells the injectors to inject less fuel.

The fuel trims in OBD tell if rich, anything over 10% added or plus is too rich.

 

Highly possible. Say only ONE cylinder leans way out, the computer can only give more gas to ALL of them, it cannot add for just one only. The one running lean gets 'fixed' at the cost of the others which were running fine now being too rich. A very common way for it to play out.

 

If it is one cylinder lean, how can that be diagnosed?

 

I'm sorry you are going through this. It sounds quite frustrating.

A couple of years ago, my girlfriend had a friend and her car ate catalytic converters. No one could figure it out or they didn't want to, but the car was running on the rich side. So I told her every 2-3 years (when you get the P0420 code), pick up a cheap cat off of eBay (less than $100) and bring it over with a case of cheap beer (PBR) and I'll install it. It was 6 bolts and the downstream O2 sensor, reset the computer and she was good to go for another 2-3 years. I'd have it done in about 30-45 minutes, just enough time for her to have lunch and a good "hen" session with my girlfriend.

If the car is running rich, there is no reason to throw the best most expensive catalytic converter on the system, it may die a slightly slower death than the cheap ones, but it will still die.

 

Thanks. Great minds move in the same direction. I was thinking along those lines, too, but Austin Transmissions, the shop the former owner used, is honoring its 12 mo. 12k mi. warranty as I text. It charged a fee of $90 so it can do its own diagnosis. Since it's a cheapie, they're just out of an hour of labor if they know what they're doing. They still made a bundle off of the $1500 they charged former owner. Left car there yesterday. I was surprised that the shop would honor it. He even knows I'm the new owner. I thought we'd have to do this under a pretense of ownership. I was thinking what if the Rislone cat cleaner I dumped in on Sat. did its job and it doesn't throw a code. It can work within 1/4 tank; my light didn't go off, but it's running like it did before the light came on. It can take up to 250 mi. or money back. Light didn't go off after running down to reserve fuel light. I unhooked the battery; hooked it back up; light didn't go off. Must need a reset. How do you reset the computer? That reset might've been all I needed to do. Rislone says use it four times a year to keep it clean.

 

When you disconnect the battery it clears the codes, then you have to run a "drive cycle". I haven't been able to find a clear defined "drive cycle" on-line -- just bits and pieces in my service manuals.

I can't speak to the "Rislone Cat Cleaner" -- never used it. My thought process always was... I can get a cat from $100 and stick it on -- knowing that will fix the problem, why spend $25-$30 when this product only might delay the problem. Again, just my two cents.

That is good news that the other shop is going to cover the cat under warranty, but I'd still want to know if the car is running rich. I'd be curious as to the "final verdict" when they do their $90 analysis. Please post when you get the results.

 

See post below.

 

Wellll, I picked up the Versa with its new cat yesterday after their keeping the car hostage for a week. Perhaps they thought it best to not drive it, but they didn't explain. Their analysis was simply, yeah, it was clogged. the rear one's mesh was pretty much fused. I'm told some folks just poke that one out with a stick. LOL The supplier of said cat honored the warranty, but not the labor. No charge for analysis, but installation was $91. Not bad. Transmissions is their forte, as they didn't have a 5 gas analyzer, nor any way to measure fuel trim, but one of his employees also works with a high performance shop in town, and he's to provide contact information. He thinks they have the sophisticated equipment and knowledge to figure out the fuel trim and air/fuel mixture. I'm thinking it's running rich. He even said the cats only last a little past warranty. Seems wasteful; why not fix. Thanks for all you advice and counsel. Your PBR approach for flat rate used to be my measuring instrument in my younger days for not only work tasks, but travel and recreation as well; kinda stopped that sometime in my 50s or 60s, can't remember exactly when. LOL.

 

kinda stopped that sometime in my 50s or 60s,

I just turned 60 -- I'm a little slower crawling underneath cars, but I can still get the job done -- most of the time. I'd prefer a nice Guinness, but I'd feel bad asking for expensive beer from my girlfriend's friend. PBR is fine (for me).

I was re-roofing my garage about a year ago, and I noticed I could only carry 1/2 bundle of shingles up the ladder (instead of a full bundle). I mentioned this to my doctor during my annual, he told me be happy I could still get up on the roof.

 

Uh, any cheap OBD code reader can read fuel trims on the fly...............no need at all for sophisticated equipment.

 

thanks, I even bought one of those at harbor freight a few months ago and I've never hooked it up. Been a little intimidated. How dummy proof are they? I guess it's time to go to the web and see what it says how to do that. As they say, in this information age, ignorance as a choice. LOL

 

Biggest issue I've seen using a phone is making sure phone is paired to the OBD adapter correctly so it can communicate with it. Bluetooth must be on and working of course.