NCC-2569

iTrader: (1)

Hi guys,

I have noticed something in my datalog today and am wondering whether it's caused by an exhaust leak or not.

Please take a look at my attachments, where you can see that my engine was at operating temperature, has run for a while and that it's somehow running in open loop.

Seeing the graph, the O2 sensor looks stuck. I was accelerating in part throttle at the time, loop was closed before and then switched to open again.

As I ended my drive and backed up into my parking space, I noticed that the loop turned to open in idle and closed when I accelerated the engine until I let go of the gas pedal, when it returned to open.

I believe the graph should look more regular than this one. Does someone have a proper one for me? Is my sensor defective?
The O2 sensor has been swapped out in late 2011 (as were all 8 injectors, so they should be ok).

There are also NO error codes AT ALL and I do know there is an exhaust leak somewhere in the rear part of the driver's side.
Could it be possible that this leak somehow influences my O2 sensor values up by the header? Seems quite far away for an influence there.

It doesn't always stick around at .2V. Sometimes it sticks around at .6V or .5V and at other times there's ups and downs like earlier on the timeline, mainly when I accelerate.

NCC-2569

iTrader: (1)

Come on, guys... someone has to know something...

NCC-2569

iTrader: (1)

My exhaust leak ist directly behind the cat, btw, and also one around the muffler entry pipe.

blacksunshine'91

iTrader: (10)

I'm curious about the cause as well. My O2 has had similar issues at idle. When I review the data, my 02 sensor readings are all over the place.

Tuned Performance

iTrader: (92)

If the o2 is sticking at .5v its bad. If you are running headers the o2 may not be heating up to 5-600f and will not become active until then and you should install a heated o2.

blacksunshine'91

iTrader: (10)

I have headers and I installed a heated 3-wire a couple years ago.

Tuned Performance

iTrader: (92)

The heating element could be the issue for it being inactive at idle

NCC-2569

iTrader: (1)

Mine's not heated and it's not permanently sticking at .5V.
Sometimes it's sticking at .7 and other values and then it goes all over the place when I rev the engine or drive.
The ups and downs of the graph are just absolutely irregular, plus I never had a SES light coming on because of it.
A dead sensor would invoke SES as soon as I move at constant low speeds for about two minutes, IIRC.
That's what's so puzzling.

Stock headers here, btw.

jermdm

Normal o2 sensor readings will fluctuate up a down. An exhaust leak at the converter and after will not effect the o2 sensor reading since the 02 sensor is before the cat. The only way an exhaust leak will effect the o2 is if the leak is at the manifold or y-pipe connection at the manifold..

NCC-2569

iTrader: (1)

Thanks for the update.
So this only leaves the sensor itself as the cause, right?

Ed1LE

iTrader: (39)

Did u figure out the problem? I have same issue. I had a couple bad injectors so just put in a set of freshly cleaned and tested LT1's but at idle my wide band afr gauge slowly but steadily creeps up to 17 from 12. With old injectors this happened to point of maxing out gauge on lean side and car would break up and sputter under acceleration. Haven't driven it yet with new injectors but gauge, to me, indicates I still have an issue.

NCC-2569

iTrader: (1)

Nope, I haven't figured it out yet.
As my injectors were mostly dead, the car leaned and riched out, according to my SES, but that's never happened again since the replacements came in.

Mr Froman

Okay, normal O2 sensor readings should fluctuate up and down between 200-900 mV VERY rapidly. It is constantly taking-giving-taking-giving fuel, with the appropriate mixture falling in the middle. Low O2 readings indicate a lean condition. High readings indicate a rich condition. Constant and RAPID change from low to high is good.

A STICKING reading indicates a failing sensor. They get sluggish when they die.

If you want to be absolutely sure that it is the o2 sensor and not the wiring/computer, you can give false readings to your computer. This is assuming you have a single-wire sensor. Unplug the sensor. Go to the HARNESS SIDE. Leave the sensor alone. Start the vehicle while monitoring o2 sensor readings. With the HARNESS SIDE to ground, you'll get one end of the spectrum. Now, using your body as a resistor, touch the harness side (using a jumper) with one hand and touch the positive terminal of the battery with your other hand. It will jump to the other end of the spectrum. By doing this, you just confirmed the entire circuitry is operating correctly all the way to the O2 sensor.

NCC-2569

iTrader: (1)

Thanks for your advice! I had my O2 sensor replaced today. Couldn't get it out at first, because someone had screwed it in at an angle. Whoopee!
Now this is how it's supposed to look like, more or less. Any irregularities must come from somewhere else.
No more leaning out or rich condition for me now!