I've been dealing with the P0430 code (bank 2 catalytic converter inefficiency) for months now on my 2007 GS350 AWD, went 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 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, heard of others solving the issue, at least temporarily with cataclean so I decided to try that. For context, my MPG seems to be on the low end (17 MPG city) and my engine also burns a lot of oil, anywhere from 0.75 liters to closer to 2 liters every 1000 km, so I figured it very may well be my cats being inefficient due to the oil being burnt, and the cat cleaner would at least temporarily fix that. It had been fine until now in terms of drivability and performance. Couldnt find cataclean here in Canada so I used another cat cleaner from the brand Duralube.

It drove fine for maybe 100 km but suddenly while accelerating fast my engine started sputtering and even died. At that point I still only had the code P0430. Then later I tried replicating the issue, the engine revs fine when not under load (in park) but when I tried speeding up in first gear it started sputtering really bad at 5000 RPM and I had to restart the engine for it to stabilize. Then I checked the codes again and had P0300, P0302, and P0304 (cylinders 2 and 4 misfiring, both of which are on bank 2). Since they're on the same bank I think that may be connected to the cat inefficiency, I'm just confused as to why it happened so suddenly for the first time, which makes me think it had something to do with the cat cleaner I put in my gas. I also realized there's a lot of smoke with a burning smell coming from the exhaust. What should I do now, change sparkplugs, sparkplugs and coils, or is there a way to do further diagnosis to narrow down the issue to know if its coming from the engine or from the exhaust (catalytic converter or O2 sensor)?

 

2 litres 1000km,s your engine is well on its way out don't throw parts at it.

 

This is my first car which I bought just this May, extreme worst case I'll engine swap it but I'd prefer to find a cost-effective solution first. Its old obviously but at 200k KM I'd expect a Lexus engine to have a lot of life left in it, even if it requires some work after whatever caused it to start burning so much (stuck rings I'd assume which appears to be the most common case).

 

I think you have a number of issues going on.

1. The spark plugs, the coils what brand did you use? How much did the spark plugs cost you? There are a lot of fake spark plugs on the market. The coils, did you use oem or aftermarket, do you still have the original old ones?

2. Concerning the oil leaks! Have you visually inspected the engine to see if you have any leaks? Like the oil pan, front crank seal, and valve covers theses three are common leaking points.

3. AWD has an issue with the design of the exhaust. They placed tin covering on the mid pipe, that has fiber insulation. That fiber holds moisture, and slowly rots the mid pipe. What I would do completly remove the tin covering the mid pipes, and that way you can see clearly if there are any other exhaust leaks as that is the most common place for leaks. Usually the cats on lexus are very strong and durable. But, if you had a misfire for a very long time then that can destroy them.

4. How often do you replace the oil and filter? Our cars need to have the oil changed earlier then most cars. 3,000 mile oil changes is prefered imo

 

Thanks for the insight;

1. The previous owner never changed them, so I think both coils and plugs are actually the same ones from the factory and were never changed at all. I was planning on replacing the plugs in the spring and doing a piston soak at the same time, just cant figure out how to remove the plastic intake plenum which covers the driver-side coils.
2. Just looking at it I don't see any oil nor do I see any oil where I park but I guess its still possible since I haven't inspected those specific areas you mentioned, but I cant imagine I'd be leaking that much and not just see it on the ground. I had assumed its all being burnt.
3. I've never inspected that area to look for that covering, if you have a picture so I know what to look for next time I have it on a lift that'd be helpful.
4. I change them at about 5000 km, just over 3000 miles

 

I would replace the sparkplugs, there easy to do you can find videos on youtube. Make sure to use ngk 3473 (FK20HBR11) buy them from a reputable seller, as there are a lot of counterfeit plugs, they usually cost $9-12 each plug. Next, I would verify that the coils are original and not aftermarket if they are aftermarket the should say denso on them.

The exhaust mid pipe, its clear to see the tin covering. They wrap only the middle pipe with a thin metal, thats held on with straps that are 10mm almost always they are rusted, and easiest way to remove them is with an angle grinder or a set of pliers and twist/cut the thin tin metal. After you remove the covering, have someone block off both exhaust tips with there hands while you inspect the mid pipe area for any hissing leaks in the mid pipe.

For the oil leaks, you got to put the car on a stand, maybe remove the bottom splash gaurd, and with a flash light visually look at the areas I mentioned. You can do this when you change your oil, because in order to do the oil change they remove the splash gaurd and raise the vehicle.

 

Thanks for the tips, the issue was actually just that the driver side primary cat somehow became dislodged and clogged the secondary cat. Ended up having to take it to the dealer to figure that out, they left the car with the rear O2 sensors out so its driveable. They said they used a camera in the O2 sensor hole and saw that the driver side cat was completely gone from where its supposed to be, and the passenger side cat is cracked. They also changed the sparkplugs and tested the compression, the average compression was 150 PSI. I then took it to an exhaust shop where they replaced both secondary cats with straight pipes, meaning I now have no secondary cats and only one primary cat on the passenger side of the header.

My main concern now is will the uneven backpressure cause any issues in the engine? I was considering getting PPE headers but heard there are cheaper alternatives on eBay, but cant find any. If I can find one, I also wouldn't have to worry about the cracked primary cat on the passenger side eventually breaking loose and causing the same issue again.

Interestingly, I no longer have any lights on the dash, I thought I would still have the P0430 code due to not having a cat at all on the driver side.

 

I bet your code comes back in the next 10-20 trips. When you disconnect the battery or reset the stored codes, it takes a certain number of drive cycles for the monitors to start reporting those kinds of conditions.

 

The GS350 has 4 cats, 2 on the exhaust manifold, and 2 on the mid pipe. So you deleted all the cats except for the passenger cat on the exhaust manifold. I doubt backpressure would be an issue. Maybe exhaust flow could be an issue, being one side is a bit more restricted then the other side. What I would do, is look for a used exhaust manifold and cat for the drivers side, and simply bolt it on. This should balance things out. But I doubt you would cause major issues leaving it as is. Maybe one side of the engine will run richer then the other side.