New catalytic converter pipe failure.

[gw33gp]

I installed a complete Walker catalytic converter system last year in July. A couple weeks ago on my way to work in the morning, my exhaust suddenly got really loud. I thought my Gibson cat back with over 250K miles had finally failed. When I got to work I checked it out and the Gibson system was fully in intact. The sound was further up the exhaust and I found an inch size hole between the two rear cats.

There was no sign of impact and the hole is above the transmission cross member and slightly in front of the transfer skid plate. That is a pretty protected area. I am baffled as to how that could happen. The only thing I can come up with is, the pipe was originally defective and just blew out.

It is well within the warranty period but since it is over 90 days, Rock Auto required that I buy another one and they will refund the cost as soon as I ship the old one back to them. I think they also have an option that I ship the old one back and once they receive it and determine it was not my fault, they would ship a new one to me. That would mean my truck would be parked for near three weeks. Not an option for me.

Any other ideas as how this could happen?

 

[Roert42]

Looks like something was welded there, and the weld rusted and broke. O2 sensor maybe?

I had a similar thing happen to the hanger bracket on a Cat for an old chevy I had.

 

[55trucker]

Indeed, that is where the O2 bung was welded in, if that is *as you say* a Walker cat assembly they use stainless for the shell of the cat but the piping is aluminized so that portion will rot.

 

[gw33gp]

The O2 sensor is on top and on the other end of that pipe. It is possible someone installed the O2 bung there by mistake and just tried to fix it resulting in the blow out.

That pipe is stainless. I don think aluminized pipe would hold up to the temperature in that area.

 

[Roert42]

It's possible there was an O2 bung that was not being used for your truck, so it was plugged with a bolt.

 

[Dirtman]

That pipe is stainless. I don think aluminized pipe would hold up to the temperature in that area.

Its 409 stainless steel. Sometimes a cat will have multiple o2 bungs so they can stretch one part into fitting more vehicles. I would think you would remember a bung being there when you installed it though?

Anyway if a bung was there and it was welded with regular e70s instead of e309l filler it would have been destined to crack and rust around the edge of the weld bead from day one. Eventually one good jolt of pressure and POP!

I just don't see why a bung would have been welded in there improperly on a new cat.

 

[55trucker]

The O2 sensor is on top and on the other end of that pipe. It is possible someone installed the O2 bung there by mistake and just tried to fix it resulting in the blow out.

That pipe is stainless. I don think aluminized pipe would hold up to the temperature in that area.

I was under the impression that with the '01 year the rear O2 sensor is placed between the cats, Now my '98 has the rear O2 sensor behind the rear cat (go figure the move with the newer models), you should also have a another two sensors upstream of the pre-cats.
As for the pipe makeup OEM is 409 stainless, Walker does state in their website they do use aluminized where piping between their cat assemblies is concerned, major reason why I will not purchase one of their pre-manufactured assemblies, instead I'll fab up the entire assembly from Magnaflow cats.

But I'd suggest just getting that opening welded up & keep motoring.

 

[gw33gp]

I received the new cat today. I just looked at the area to see if there was any indication of anything there. I was very surprised. That is where the hanger bracket was welded. That was hinted at before but I didn't think to take a look. The hanger bracket had fallen off after it broke out of the pipe and I didn't see it was missing.

Mystery resolved. Now, I need to get it installed and get the broken one shipped back to get my warranty refund. I hope that goes well.

 

[Roert42]

Had that exact issue with with a walker cat.

 

[gw33gp]

I might have found the reason for the failure of the catalytic converter pipe where the hanger was welded. I discovered the muffler hanger was broken. It could have been the broken hanger at the catalytic converter caused more stress on the muffler hanger and broke it but I think it is more likely that the muffler hanger broke causing more stress on the catalytic converter hanger, contributing to it breaking. I think it should have been strong enough to hold up anyway.

Gibson's muffler hanger is welded to a muffler clamp near the back muffler clamp. So, there are two muffler clamps on the rear of the muffler with one being welded to the hanger. That area where the weld is does not have much beef to it to start with and having over 250K miles on it would seem to make it prone to failure. I can't prove either way but I know what it suspect.

Fortunately, it was covered under warranty and I got a refund.