Hi there,

Trying to bring my 2004 V8 4runner back to life. I got a p0430 All instructions pointed to find leaks first before a condemning CAT.. so I put a shop vac in reverse into the exhaust. Found a leak Right by passenger side downstream 02 sensor btwn the Y pipe and manifold cat.. Just confirming a leak here would this cause a Cat code? its right near the downstream 02 sensor, so I assuming it will and it should cause the 02 sensor to be jumping around.

Next, I was looking at the Y pipe. And looks the y pipe doesn’t look oem. Looks like the driver sides Y pipe flange was cut off and repaired. That seems like a solid weld that is still holding, but I can’t really tell if the Y pipe is original. it looks looks aged just like the original piping, but is it purposely restricted like this from the factory? The pictures of other y pipes i found on the internet look like they were for the v6… can with any one prior experiences let me know if factory y piping? Or did someone fab the Y pipe like that?
If that is a factory Y pipe, would the next logical step to bring my car to muffler shop to redo the header to y pipe flange? Its leaking btwn the two flanges and at the flange weld.

So I’m I correct in thinking that fixing this leak ‘should’ solve my P0430 ?
EDIT: If that’s not the factory Y, I could see why that restriction could cause the cat to burn up.

TY

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It's the factory Y pipe. The most restrictive factory exhaust in the history of cars. Whether or not it's been modified at the CAT, is highly possible. The 0430 code could be from the leak, bad CAT, or faulty o2 sensor.
You can try to swap sensors from right to left and see if the code follows the sensor. Then you know it's that sensor and will need replaced. There are numerous replacement Y pipes, but the only one I have experience with is the Doug Thorley Y, which I couldn't find on their site. They may not produce them any longer. The leak should be fixed to avoid any other problems it might create.

On a side note:
The gov has decided that the less than 1% of the population who produce or use performance exhaust modifications, are evil and the cause of all the world's problems. So a lot of cost effective exhaust solutions for us consumers are no longer available due to fines imposed on the producers of these products.

There are some states that will fail an aftermarket exhaust system that produces less emissions than the oem system, simply because it's not "factory". So some 4Runner owners are stuck w the worst factory exhaust ever produced, which costs a fortune to replace. The deck is obviously stacked against us....

Looks OEM to me except where that welded in piece is there was probably a failing flange like the leaking one. I would start by having that flange repaired too. Will it fix the code? Maybe, maybe not but it's a good start.