Man :/

[Junior2552]

So today a van that was driving in front of me dropped off the entire back half of it's exhaust. While I did my best to straddle it (couldn't go right or left of it..), it cut a hole in my Cobb downpipe.

My car now runs on the richer side of the spectrum, and I'm not entirely sure why. Is this because the second O2 sensor is responsible for injector input, and isn't getting a very good reading due to the hole in the downpipe? If I plug the hole, will it read accurately again?

Secondly, I'm going to heat it up with a torch, fix the crease, and weld it shut. Is there any reason I shouldn't weld it? It is stainless, and I've been welding for a few years, so I figure it couldn't hurt. Any objections? Thanks!

[SeattleJeremy]

That's a heck of a problem.

Yes, it's running rich because the O2 sensor is getting faulty readings (exhaust gasses are escaping from the hole before the O2 sensor can read them).

Don't drive it until it's fixed (or at least stay out of boost). It defiantly couldn't hurt to try to weld it first. If the weld fails it will be running rich again though, so keep an eye on it. A wide band O2 sensor/gauge would help you with that.

If the weld does fail I suggest getting a new down pipe.

[TheJ]

That sucks!

[Junior2552]

That's a heck of a problem.

Yes, it's running rich because the O2 sensor is getting faulty readings (exhaust gasses are escaping from the hole before the O2 sensor can read them).

Don't drive it until it's fixed (or at least stay out of boost). It defiantly couldn't hurt to try to weld it first. If the weld fails it will be running rich again though, so keep an eye on it. A wide band O2 sensor/gauge would help you with that.

If the weld does fail I suggest getting a new down pipe.

I'm using an AEM UEGO to get the AFR's! But I appreciate the suggestion! I'll try to weld it tonight! I'll let ya know how it goes! Haha.

[teflon_jones]

I'd weld a piece over it rather than trying to just weld the crack. It's going to be difficult to get a good bond on that surface, but you can weld to the outside pretty easily since you can clean it right up. Just get a thin piece of plate that's a 1/2" wider than the hole on all sides.

[Junior2552]

Funny you should suggest that, teflon. That's exactly what I did! I used a piece of 3in piping, cut it in half, and welded it over the hole after I cut out the damaged part. But I'm confused because I'm still running a little rich while I'm just cruising around town. 13.9:1, up to about 14.4:1. I realize that's not much of a difference but the car consistently stayed at 14.8:1 AFRs while cruising on highway, city, anything. Any suggestions? I know that the last flange by the muffler is leaking pretty heavily as it got damaged as well, would that make it run any richer? It's after both O2 sensors, so I'm running out of ideas... Suggestions! Thanks!

Edit: I can hear a very vary faint whistle from under the hood. I can't differentiate between it being turbo spool or being a boost leak, especially because I don't know what else is damaged. Could it be possible that my up pipe got knocked loose? That's my I'm running rich? Something PRE turbo?