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So after a semi-fruitless install of my new turbo-back exhaust system on Saturday I decided to take it to a shop to have them install that as well as a set of brake pads. So I get the car back today and of course there is a problem. The mechanic tells me that the car is running rough. I go around back and start her up and it stumbles for a couple of seconds and stalls. I smelled the exhaust and it smelled strongly of gasoline so it must have been running too rich. The car was running perfectly when I brought it in. The only thing I can fathom is that maybe there is some malfunction with the O2 sensor. I'm under the impression that without a proper reading from the sensor the ECU defaults to a rich setting? But I have no idea otherwise. All I can say is that I'm uber pissed. I hope the mechanic finds the problem tomorrow. Any thoughts?

It certainly could be an oxygen sensor problem. The sensor could have been damaged when being removed from your stock exhaust or when being reinstalled on the new exhaust. Or some of the wires might have been mixed up when extending the wiring. Or the connections might not be solid (it's hard to solder to the weird alloy that the stock sensor wires are made of).

The ECU will run fine without the oxygen sensor, so the first thing to try would be to disconnect the sensor, disconnect the negative battery terminal, press the brake pedal for 30 seconds or so, and reconnect the battery terminal. Leave the sensor disconnected and see if the car runs. Without the sensor the ECU will just fuel based on measured airflow, running probably a little richer than usual and with less spark advance than usual. But it will run fine. My car passed an emissions inspection without the sensor, in fact.

Realize, though, that these cars always run really rich when starting cold. And any kind of misfire will throw raw fuel out the exhaust. So you smelling raw fuel at the tailpipe doesn't necessarily mean it's the oxygen sensor.

I can't think of other exhaust-related things that could cause the car to run rough... is it possible that he disconnected some intake tubing and didn't reconnect it properly? An intake leak could be the culprit.

I dunno, I wish I had known you were going to do that. I would have offered to meet you somewhere and help you install it.

Make sure all hoses are hooked up, and everything.

Even o2 sensor unplugged, the car shouldn't stall.

vrg3 wrote:I can't think of other exhaust-related things that could cause the car to run rough... is it possible that he disconnected some intake tubing and didn't reconnect it properly? An intake leak could be the culprit.

Thats what I was thinking. I noticed that he replaced one of the bolts holding the air filter box in place. Whether that means he disconnected something or just decided to replace soem basic hardware I don't know. Its very possible that there is some intake leak, in fact he said that is one thing he will look for tomorrow. Thanks for your help Vikash

is the maf pluged in???

So I got the car back today, the mechanic said that there was some issue with the O2 wiring. Anyways the car is LOUD and still running kinda rich. I love how it sounds when idling but it seems like its gonna attract the wrong kind of attention. So I think I'm gonna go with another muffler. So my new question is will welding the stock muffler back on create too much back pressure or is there another muffler what isnt so loud that anyone can recommend. My ideal set up would be to hack a couple of inches off the OEM mufflers dual tips and stick a pair of slightly larger and prettier tips.

Yea, Jason's exhaust was WICKED loud up top.

Magnaflow mufflers have a nice tone. See my dyno video for a clip of my system. That's got a resonator in it too though, which I will be hacking out soon.

Putting the stock muffler on would not be even close to optimizing the system you have.

Do not replace the muffler! Add a resonator to the mid-pipe. Trust me, it will help mellow the exhaust note a bit and should be cheaper then a whole new muffler.

Yeah, that's a good idea, Matt! You could easily weld or have someone weld a resonator into the midpipe. The midpipe's mostly just a straight piece of pipe anyhow.

Or if you wanted to spend a little more money maybe you could replace the gutted cat with an actual cat.

vrg3 wrote: Or if you wanted to spend a little more money maybe you could replace the gutted cat with an actual cat.

Does that mean it'll sound like a Jagular?



Which breed works best? Domestic or Feral?

91legacy_sleeper wrote: Which breed works best? Domestic or Feral?

Awesome! How cool would it be to have a pet jaguar?

What size tip is the muffler? A silencer works wonders. It is rougly equivalent to an inline resonator.

My question is why the mechanic had to mess with your airbox?
I know when I had my exhaust done last, they didn't even open the hood. From the way you've worded it, he's monkeyed with something that wasn't included on the work order, so he's responsible for anything that went wrong as a result of the rogue work done --which includes the result of running rough/stalling out, which may be an issue of the intake, which he obviously did something to, as you said a bolt/screw was replaced on the airbox.
It was just exhaust work?
'splain, yo.

91White-T, I was referring to vrg3's statement of saving money by using an actual cat.
'Powered by Tabby'.

Hehehe... Maybe you'd want the earth-moving power of a Bobcat.

With turbo models you do need to pop the hood because you need to unbolt the downpipe from the turbocharger, and some of the fasteners can't be reached from underneath.

And removing intake plumbing makes that easier.

I am going to do a downpipe install on my friends WRX on Saturday. I hope I don't fuck it up, lol. Nah, should be pretty easy. He, too, has an HKS downpipe.