Nightshade

So as of recently my car has been using waaaay more gas than usual. According to my trip indicator, I've gone only about 50 miles and used up half a tank! And I'm positive it's not just a float switch issue either, because the numbers do add up at the pump. Not to mention the black soot coating the inside of my exhausts. The computer's error code is 'banks 1 and 2 system too lean' but with all this modern computer crap that could be anything. My assumption at this point is that it has something to do with my lack of catalytic converters, which even if that's not the culprit I still want to bypass those sensors eventually.. So simply put:

1. How would I go on about bypassing the catalytic converter sensors?

2. If you had the same problem with your LS1 4th gen, how would/did you solve it?

Thanks CZ28! Also I'm having my mechanic friend check it out tomorrow morning. So I'll see what he says/does first.

..DAMN..

Check your o2's...

Injuneer

"Bank 1 and Bank 2 lean" have nothing to do with the after-cat O2 sensors, which are the ones that are used to monitor the cats. Those sensors do not materially affect the way the engine runs.

The codes indicates the pre-cat sensors are telling the PCM the engine is running lean, and the PCM is pouring in extra fuel to try and correct that (perhaps "false") lean condition. Even by adding the extra fuel, the lean condition has not been corrected. The evidence would suggest that your O2 sensors are reporting a "false" lean condition, causing the PCM to add extra fuel that isn't really needed.

You need to check the O2 sensors and the long term fuel corrections with a scanner. That will confirm if its a "false" lean. Then you need to find out why the O2 sensors think your exhuast is lean. Could be due to misfires, could be due to exhaust leaks before the O2 sensors, could be due to faulty sensors or faulty sensor wiring.

Nightshade

Yeah that seems to be the obvious answer. And actually I found out the post cat o2 sensors are simulated, probably so the last owner could get past Chicago emissions. The pre cat sensors I would imagine are covered by carbon buildup due to aftermarket headers and filter (more air+more gas=bigger explosions=more carbon..) which is probably whats just murdering my mileage. (8 MPG is the official count as of today..) So is it worth putting on new o2 sensors if that's the case, or should I just say screw it and get the pre cat sensors simulated as well?

Also thanks for putting up with my, er, noobishness where such things are concerned. Still on my first year with the car.

Injuneer

The fact that you installed a larger exhaust and air filter will not cause:

Both those changes will improve the engine's breathing. The MAF sensor measures that increased air flow quite accurately, and the PCM adds only the extra amount of fuel required by the extra air flow. Those changes should NOT cause it to run rich, and should not cause the O2 sensors to carbon up... at least if there are no misfires, exhaust leaks, or screwed up O2 sensor.

You apparently feel my answer is to "obvious".... but that's about the best I can do. Maybe someone else can come up with a less obvious answer.

Nightshade

Not like that, haha. Don't get the wrong impression, I really appreciate the help. It's just thus far your answer makes the most sense.

..DAMN..

I wanted to quote you on this becuase 4 day's ago my car started getting horrible gas mileage too i actually burned up a half tank of gas in one after noon driving around town paying bill's and such.

Also my check engine light would come on after the car was warmed up so i knew it was an o2 i replaced the passenger side o2 and after about 10miles of driving everything was fine again!

I feel your 8 mpg man...lol