Worse mpg followed buy dreaded p0430 code

Just looked at magnaflow and they won't even sell me a converter online.

 

@eccracer104 works for a major auto parts company I can't remember the name of in San Diego and offered to help me get the Magnaflows, I found a shop locally though. Maybe he can help

Edit: its AutoAnything

 

Christ...

P0420 and 430 codes. They set for a reason, typically it is gonna be due to an overly or overly rich condition. Typically it is an overly lean condition. The prime suspects are typically misfires from neglected plugs or failing coils, the very prime suspects after that is the mass air flow meter and the air fuel ratio sensors. In no particular order. If you want to do a great tune up and reclaim fuel mileage lost...

Replace all spark plugs, replace mass airflow sensor and replace both upstream air fuel ratio sensors.

If you have a specific misfire consider testing the coil, and if it is defective I strongly recommend replacing all 6 as the rest are sure to go out in short order after replacing just one. (Happens every time)

If cats are already fried there is no recovery from that. Not even all those snake oil additives like guaranteed2pass, cataclean, and all that junk.

 

If it is, the 4.0L CA legal cats I can't get. Was just searching for a member recently and all we could find were OEM being CA legal.

 

Weird. I guess it was just for the 3.4l v6 then? I could've sworn that Jason told me once that he could get CARB legal aftermarket cats as well, I don't think he was being gen-specific but maybe he was. That's strange, I wonder why they don't make them for the 4.0l

 

Thank you for checking on that. Appreciate it. I'm going to be removing cats and dtst and going JBA long tubes and giving CA the big middle finger to their smog shit

 

Maybe not the right place for this but I cant find any specific info that's relevant to me; I've had a reoccurring P0430 code for a while now on my 2007 Lexus GS 350, MPG seems to be on the low end (17 MPG city), and I tried something similar to cataclean (the brand is duralube, couldn't find cataclean here in Canada) and it was fine for maybe 100 km but suddenly while accelerating fast my engine started sputtering and even died, afterwards I tried to replicate the issue and my engine simply starts sputtering/stalling at high RPMs. Do you think this could be the cat cleaner? it also sounds like its misfiring.

 

Check your fuel pump, getting ready to do mine soon, same code. Also check plugs and ignition coils for the misfiring

 

Unless you have a code for a specific faulty O2 sensor , you likely have a bad catalytic convertor. Car is 16 yrs old and likely high miles so it's expected.

 

If it is misfiring wouldn't it trigger a specific code for that?

 

Should, could be a pending code.

I have a different motor but I feel a slight miss and stumble on acceleration. Had the fuel pressure tested and recommended a fuel pump and cats.

I do agree that your cat is probably toast but there is usually a reason. Bad o2 sensor, maf, running too lean or rich. Could just be old age. If there is a problem causing it it must be addressed or it will happen again.

Have you checked for small exhaust leaks near the downstream sensor/ usually under the heat shield?

 

I've gone to an exhaust shop and they said it was a leak on both pipes which needed welding, had to clear the code after I got that done and then it came back after a couple of months, cleared it again and sometimes it wouldn't reappear for weeks but now for a few weeks its been persistent and will reappear almost daily, hence why I decided to try the cat cleaner. Also, when revving the engine in park it seems fine, but when I tried to rev it high under load by keeping it in first gear, it started stuttering really bad at 5000 RPM and sure enough I got the misfire code. I had to restart the engine after which it was better but still misfiring by the sound of it. When I got back home there was smoke everywhere with a burning smell from the exhaust and the cylinders that are misfiring are 2 and 4, both on bank 2 which is also the side that the cat inefficiency code is coming from, so I'm guessing they're connected. I'm just not sure what it is, but the reason I think it may be the cat cleaner in the gas is because it started happening so suddenly and for the first time. The main reason I decided to use it in the first place is cause my engine also burns a lot of oil so I figured that could also be a factor and could at least temporarily unclog the cats.

 

Could have knocked loose enough to clog the cat?

@super_white , need some Lexus help please sir!

 

Any unburnt fuel or oil getting into your cat will destroy them pretty quickly.
A scan tool comes in real handy because you can look at the upstream and downstream sensors to see what they are doing.

 

420 and 430 are catalyst efficiency codes, the upstream and downstream sensors report to the ECM. When we see the code at work we pull up the data list and see what the sensors are actually doing. With higher mileage vehicles, the cat is usually bad but not always.

 

I have an OBD 2 scanning tool which I used to see the codes, what data should I be looking for from the sensors? The car has 198,500 km (123,000 miles) on it btw and I'm not sure if the sparkplugs have ever been changed, was planning on doing that in the spring along with a piston soak to try reducing the oil burning. Do you think it could also be the sparkplugs being fouled from the oil or from the cat cleaner in the gas? the other codes I got when it started causing issues at high RPM recently are P0300, P0302, and P0304.

 

First things I'd be doing for a complaint like that is checking fuel pressure and exhaust backpressure, relatively easy to test with the right tools.