eighty-six

Hi all,

Hopefully this is the most appropriate place for this issue. Here's the gist of it:

A little while back, I had my SES light come on and had the code checked. It was a P0420 code (Catalyst System Efficiency Below Threshold [Bank 1]). No other codes at the time, and I wouldn't have noticed, save for maybe a little loss in power and gas mileage; the substrate wasn't all broken up.

I had a local Midas run a diagnostic, and they deemed the driver-side catalytic converter bad. (The passenger side had been replaced three years ago.)

I went and bought a direct-fit replacement from Flowmaster, and attempted to install it myself. Well, wouldn't you know it, a couple bolts were rusted through and sheared off at the manifold... So I went back to Midas anyway to have them get the original cat removed and install new bolts/studs and the aftermarket converter. They cleared the P0420 and sent me on my way. (Some !@#$ing $250 later.)

The SES light came on again before I got home, and, about half the time, it idles pretty low/rough while I'm sitting at the a stop. It's been maybe a week and half since the new install.

I have yet to check the code this time, but I will do it soon and let you know. Otherwise, does anyone have any idea what could be causing this? Oxygen sensors? Faulty gasket? It wasn't doing this before the new converter, so I'm hesitant to believe it's something totally unrelated (vacuum leak, etc.) but I'm willing to look into that if I can do it myself.

The car is a 1998 Camaro Z28 with ~122,000 miles. I have fawned over this thing since I got it, so while I can't speak for the previous owner (acquired about 6 years ago at maybe 90,000-95,000 miles, I can't remember). No engine/exhaust modifications, save for air lid, MSD wires, Flowmaster muffler, and a computer tune. As far as I know.

Thanks in advance.

Roarin_8

iTrader: (5)

Might be your O2 sensors.

TheBlueKnight

iTrader: (4)

I'm thinking 02 sensors as well.

bad_408_vert

iTrader: (6)

scan codes and share what you find.

use the forums before you spend any more time / funds going for repairs.

eighty-six

Codes were P0134 and P0131 (O2 Circuit No Activity Detected, Bank1 Sensor1 and 02 Circuit Low Voltage, Bank1 Sensor1.) So definitely a sensor.

I don't recall those being there before, and hopefully Midas would have alerted me to them if they were (too naïve?), but could those have made it appear as though the cat was bad? Or is this something to be expected with a new cat? (It didn't happen with the passenger side when it was replaced.)

Could it have been something as simple as not reconnecting the sensor? Although I don't think the upstream one needed to be removed, if I recall where it is placed, so maybe it went kaput. I can get under there and have a look at some point... Not looking forward to having to throw another $70 or however much the stupid sensors are at this issue.

Roarin_8

iTrader: (5)

They are easy to change but you will need a sensor removal socket for the ratchet. You can rent them from autozone, even though I bought mine outright. Check to see if it's connected first, if it is, change both of them out since the driver side went out, the passenger side will usually follow behind it.

eighty-six

Since I hate when threads go without being concluded, things were, indeed, fixed with a new gosh-darn O2 sensor. Bought a Bosch one and cleared codes, and now it runs superbly. I may be imagining things, but the exhaust note actually got better too? (Thanks, I guess, Flowmaster.)

Roarin_8

iTrader: (5)

Good to see that you got it fixed Now keep an eye on the passenger side one.