P0420 Exhaust Leak Bubbles Between Cats 1 and 2.

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I used gumout type exhaust paste for years ; would last several weeks. easy to put on but gets old
 
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Popped the Y-pipe off. One of the nuts spun but I got it off. It boogered up the stud threads then the stud would not come out so I went ahead and took off the front exhaust manifold. Much easier to get the stud out when it’s on my bench (torch and ice method). Ordered a new stud, nut and 2 donut gaskets. I will see if I can put some welds down tomorrow and test for leaks.

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I got it welded up. Had a couple more leaks in that area than previously thought--you weld up one hole and it finds the next one and so forth. Finally got it all good to go. Pressure tested it on my bench with my air compressor. No bubbles anywhere along that crotch. I put it back in the truck last night (not an easy task getting it all lined up with the manifold!) but it was getting too late to throw the airbox, etc back on. I'll test tonight and report back.
 
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I got it welded up. Had a couple more leaks in that area than previously thought--you weld up one hole and it finds the next one and so forth. Finally got it all good to go. Pressure tested it on my bench with my air compressor. No bubbles anywhere along that crotch. I put it back in the truck last night (not an easy task getting it all lined up with the manifold!) but it was getting too late to throw the airbox, etc back on. I'll test tonight and report back.

Hey so what did you use for the weld?

I've got the same issue although I have previous owner repairs along the edges of both cats too. Looks like some kind of exhaust leak paste. I'm trying to decide between trying to repair everything vs. waiting until I can afford to replace the y-pipe down to cat #2.
 
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Standard MIG welder with .030 wire. Had to build up the weld to get everything sealed since that's a deep crevice.
 
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Wished you lived close. I'd weld that up for you. Others have reported pretty good long-ish lasting results. If you can remove that section, a muffler shop will weld that up for you easily too.
 
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Wished you lived close. I'd weld that up for you. Others have reported pretty good long-ish lasting results. If you can remove that section, a muffler shop will weld that up for you easily too.

Appreciate that. I may try to borrow my buddy's welder and try it myself or take it to a muffler shop. I am thinking I need to remove whatever crap is on the seam of the cats to see what I am dealing with underneath. The y-pipe cracks look pretty typical.
 
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Yah, you'd want to wire brush that junk off.
 

ToyotaDon

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No it’s not. I’m tempted to try a flange-style O2 sensor extender. If that fixes it, bad downstream cat. I’m curious if this one would work. Good chance the O2 sensor flange size is the same so I may try it.

The sensor extender won't "fix" it, just keep the sensor from measuring as much change in oxygen levels.

I'm wondering why you believe it would be the downstream cat. Typically, the upstream cat is the reduction portion, which contains the cerium used to store oxygen. Code P0420 refers to oxygen storage capacity, so points to the upstream cat.
 
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"fix" it, as in keep CEL from kicking on. Not an actual fix, correct.

Unsure on the P0420. Still hoping it's caused by an exahust leak at this point. This isn't my daily so I'm taking my time on it, parts-wise.

I'm all ears on any input you have for this. Thanks!
 
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Welp, I've got it buttoned back up on the rig. No visbile leaks at any of the joints, etc. I've driven it 4 drive cycles so far and no CEL or pending codes on my OBD reader. We shall see. At any rate, I'm glad I fixed the exhaust leaks, even if that doesn't fix it. I'll report back one way or another.
 

cruiserdan

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My guess is stopping the leaks has solved it.
 
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This is not my best welding work but man, that's a tough area to get into. Lots and lots of build-up required. Long electrode stick-out required which is not ideal! But hey, no leaks.

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cruiserdan

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Well done!
 
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Original leak area.

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One-Week Update. May jinx it but I’m posting, regardless. Typically I would’ve had at least a Pending by now.

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Popped the Y-pipe off. One of the nuts spun but I got it off. It boogered up the stud threads then the stud would not come out so I went ahead and took off the front exhaust manifold. Much easier to get the stud out when it’s on my bench (torch and ice method). Ordered a new stud, nut and 2 donut gaskets. I will see if I can put some welds down tomorrow and test for leaks.
@harrydunn - did you need heat to get the nuts off when under the car? PB Blaster hasn't done anything for me. I need to get some Kano Kroil as it may have been my lucky charm on a terrible exhaust manifold job a few years back. I broke out my induction heater but it had a malfunction before turning the bolt red. I hate breaking out the torch in such a tight space.
 
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Honestly, no. I live in Missouri but this rig has only lived in Texas, California and Nevada so everything comes off easily with a socket. It’s a Missourian’s dream!
 

cruiserdan

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Honestly, no. I live in Missouri but this rig has only lived in Texas, California and Nevada so everything comes off easily with a socket. It’s a Missourian’s dream!
Still good on the CEL?
 
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