moondance

My check engine light comes on and sometimes goes back off and the error its reporting is running rich bank 1. I was told that the O2 sensor could be going bad. Is this the case and if so how many is on the car that I need to replace. Also is there anything else that would cause the same fault before I try to replace something that might not need it? I was also told that if the O2 sensor is bad it would cause MPG to drop. I recently filled up and only got like 13.5mpg. Granted I do not know what it got before I bought the car but according to specs I read it should get 17city 25 hwy. Any help would be greatly appreicated. Thanks

Guess I should have pointed out its a 1997 Z28.

mrmint69

If you have a bad injector it could also cause problems. You could try just replacing the O2 on the bad side and see what happens. If you have hi miles and there origional it might be worth it to do both together.

moondance

Any signs that would lead to one or the other before I buy the O2 sensor? The car has 105k on it which it had when I got it about 2 weeks ago.

Guest47904

Assuming your vehicle is stock, it has 4 O2's. The 2 in front of the cats are used for fuel control. The 2 behind the cats are only used to monitor the health of the cats. No need to bother with the 2 in the rear.

Many peeps don't change the O2's like they should during tune ups. They should be replaced about every 60K or so.

However, there are several things that should also be replaced as normal tuneup items as well. So lets' say you have a fouled plug and the O2 is bad. If you only change the O2, the bad plug could also destroy the new O2.

An oh yeah, the air filter could also cause your bad fuel economy but since you just bought the car, I know you already checked it so it couldn't be that.

Injuneer

Always best to post the exact numerical code. But we can assume that it is in fact the one that says the left bank (Bank 1) is running rich. That code sets when the O2 sensor tells the PCM the engine is running rich, and the PCM can not correct the A/F ratio using the learned long term fuel corrections. The corrections bottom out at -15% (avg BLM = 108), and can't go any lower You need to do a data scan of the PCM, looking at both the left and right long term fuel corrections. The right bank may also be close to the point where it triggers the code for rich on Bank 2.

Knowing whether its running rich on both banks, or only on Bank 1 will tell you whether its a problem that affect only one bank, or something that is affecting both banks. That may point you in the direction of either an O2 sensor, or something other than an O2 sensor. Without that kind of info, everyone is just guessing at your problem.

moondance

Took the car in yesterday to look at a few things, they said they checked all the O2s and the one after the cat on the drivers side is bad. They said something about it bring triple didgets while all others were in the doubles. Gonna save the money up and take care of the O2, new plugs, reseal the tranny, put new front and rear seals and timing cover kit, new water pump since it will already be out and replace the oil pan gasket at the same time. They said parts and labor will be slightly over 1k and both warrantied for a year. Hopefully ill be getting a good deal.

z28camaro1090

i would seafoam it ..

moondance

not sure what that is

Injuneer

What they said about the O2 sensors makes no sense at all. The after-cat sensors do not control lthe A/F ratio, and they do not set a code for "rich". Again.... get the EXACT code. Without that, no one can help you. There is no evidence that an O2 sensor is causing your problem. If you don't have a code for the after-cat sensor, you are wasting money replacing it, and even if it was bad, it would not cure the "rich" code. Stop wasting your money and start listening to the people who are trying to help you.

Triple digits on one sensor.... double digits on the other three...... makes no sense at all. All 4 sensors should be cycling back and forth between rich and lean. Pre-cat sensors should swing over the range of 0xx-9xx millivolts. After-cat sensor should swing through a narrower range, since the cats affect the O2 content.

moondance

P0172 was the code it was throwing. Most of the money that I was quoted was for resealing the engine and tranny for the leaks it happens to have and changing out the water pump cap and rotor and plugs.

Just outta curiosity, since this thing has a K&N CAI could someone have over oiled the filter and got the MAF dirty to cause the issue? Granted the code comes and goes at will but the running ruff is always there reguardless.

Injuneer

Next step is a scan. Look at the long term fuel trims. Determine if it is only Bank 1 (driver's side) that is showing large negative numbers - that would indicate something that affects only the driver's side of the engine (leaking injector, faulty O2 sensor or wiring).

Or are both sides showing large negative long term trims - that would indicate a problem affecting both sides of the engine (MAF, excessive fuel pressure, saturated EVAP canister purge, contaminated fuel, EGR stuck open, problems with the TPS or MAP sensors)

moondance

Is there any vacuum leaks that could affect only one side? Last night when I went to the store I could hear what appeared to be a vacuum leak but being it was dark couldnt find it. Seemed to come from around the center of the enging area though about where the throttle is.

moondance

Just outta curiosity too, the car came with a K&N CAI. If I wanted to make sure the filter was all nice and clean how do I get to it? Dont really wanna sound stupid or anything but Ive never messed with one of these and this was actually the first one Ive seen.

Injuneer

A vacuum leak would make it run lean, not rich.

The filter is accessed by removing the plastic panel the seals the bottom of the fender, right above the air dam. The end of the air dam will need to be loosened to remove the plastic panel. K&N make a "recharge kit" that includes a cleaner and the oil. The filter does not need to be cleaned more than once every 25-50,000 miles, depending on severity of driving conditions. Actually filters better with a light coaring of dust on it. Excessive cleaning wears it out.

Look at FAQ questions #4 and #16:

http://www.knfilters.com/faq.htm

moondance

Gotcha. Well I guess the bigger problem is the fact the fault light is out now and it still runs ruff with bad MPG. Im getting like 11-12. Seemingly it doesnt run as ruff cold as it does warmed up. Once its warmed up it runs worse. But it appears it only is like this at idle. Driving down the road I dont notice anything.