Bad gas mileage - replace 02 sensors?

[alamantia]

I dont drive my car in the winter but I go out to the garage and start it up about once a month and drive it around the block a few times provided there is no snow or salt on the road. One time I did that and the check engine light came on, i scanned it and it showed a code for the left bank manafold 02 sensor. I cleared it and it has yet to come back on. I started driving it a few weeks ago and I can swear the gas mileage is signifigantly worse than it was last summer. I'm wondering if I replace all 4 of the 02's if I will get better gas mileage. The car has 34,000 miles on it, its a 2002 Z28 with only full length headers, cat back, 4.10's, lid, MAF, 180 stat and tune. Would you reccomend I change the 02's. I look on GM Parts Direct and they dont list them but i can assume that they are not cheap. I figured they would last longer than 34,000???

[JL8Jeff]

What kind of mileage are you getting? If those are the original O2's and were transferred from the manifolds to the headers then yeah, they probably should be replaced. Header burn off can mess them up as well as any impact from trying to remove them from the manifolds can hurt as well. I think the correct AC Delco O2's are around $75 each.

[HardcoreZ28]

Could be the O2's. Does the car feel down on power at all as well? Maybe something else like a dirty fuel filter hurting you too.

[sweetbmxrider]

or bad gas? some cheapo stations throw regular in super. bastards.

[alamantia]

i dunno, it still has power, car still runs 12's, i understand about header burn off but they are stainless, the only thing I can think of that would burn off would be a little oil residue from the mandrel bender that didnt get totally removed in the cleaning solution, but 02's shouldnt be effected by a little oil burn off anyway. I put Sunoco in it. Too bad 02 sensors werent 8/80,000 like cats. I will see what my dealer connection AKA Dad says, maybe I can get them super cheap, I just dont want to ask for things I dont need.

[Tru2Chevy]

Does your scanner do datalogging at all? If so you can either log some driving time or have someone else in the car watch the scanner and see what the O2 voltage looks like under normal driving. I had mileage issues with my old Lumina a while ago and suspected the O2, but I messed with the scanner first and found it to be still alive, but pretty lazy.

Might wanna check before throwing $150 at it for 2 sensors.

- Justin

[ins0mnia24]

yeh Anthony see if you can get your Dad to snag the Tech2 and drive a few miles with you while monitering both banks of your front O2 Voltage you should see voltage from 10-800 Mil volts and the voltage should jump around to different volts constantly ..
If it was your rear O2's it wouldnt affect how your car runs it would just set off the SES..

[alamantia]

i concur

[camaro2you]

My car was doing the same but worse I kept throwing lean code's every time I would get on it. Picked up two bosch sensors that are rear o2's for a corvette. They have longer wires so no extensions are needed and they are also heated and now the problem is gone and the mileage has gone back up.

[sweetbmxrider]

don't heated O2's have separate wiring and other crap with the computer?

[Pampered-Z]

One quick suggestion, next fill up all some fuel system cleaner. Could just be some varnish or dried gas in the injectors? I drive allot of miles weekly and monitor my mileage. I noticed my MPG dropped by 2, I changed plugs ( plugs had about 60K on them ) and added Lucus fuel system cleaner and the mileage went right back to where it was.

If you replace the O2s, start with just the front ones, they are what the ECM uses to read Rich/lean, the rears are just to ensure the cats are working.

[alamantia]

I got two new Delco 02's courtsey of th ol man, i will install them at some point this month and let you know the results.

[alamantia]

prior to installing the 02's I scanned it to find out that while reving the engine to about 2,000 RPM's and droping it to idle the left bank was still showing about 500-600 millivolts while the right bank was showing around 100-150 at idle. Eventually the left bank 02 would come down around 100-150 wher it should be, but during the interum i was getting a misfire on the #1 and #3 cylinders, im guessing because the injectors were dumping too much fuel on the left side, which would explain why my gas mileage is so poor, but hey its better than running lean right? Now upon removing the 02's it dawned on me that I used extenders when installing the headers, im sure the 02's is actualy fine and the extenders is making it lazy, i have actualy read about this on tech, now do I install new 02's using the extenders or buy bosch 13111 sensors to avoid this in the future, hummmmmmmmmm...

[camaro2you]

I would pick up the bosch's and ditch the extensions whenever you decide to replace them.