legacycentral bbs

Just curious, what's stiochometric value for the O2 sensors are.

My mileage has been utter crap. Barely pushing 20 mpg, and that's with a n/a motor. I did have the torque 2 chip in, which didn't help, but it wasn't much better without the chip.

Without the chip in, and reset ecu, on a steady pull I get a value of around .8-.9 It will vary all over the place too, which is weird, and there are other times when I'm coasting to a stop it goes super lean 0.2

I guess I'm looking for others that have viewed their O2 readings to see what's sort of normal.

I really think I have a vacuum leak between the intake manifold and heads.

I need to check my plugs too. They may be completely fouled and nasty.

Anyone.....nobody has a clue.....

bueller.....

What makes you think the O2 sensor is bad, other than the poor mileage? Dropping down to a low value during deceleration is normal, to my knowledge, indicating a lean condition. How do you have your sensor hooked up so that you can monitor the voltage? I may be able to hook into my car and get some values to compare. I haven't done much in the way of mods other than a K&N filter and MRT exhaust system for a 2.5. I regularly get 28mpg with a combination of 80mph highway stints and 40-60mph twisty backroads (and that's just going to work!). I also run the A/C quite alot, but relax a bit when it comes to accelerating.

Sounds like similar values to what I'm getting.

I don't think my O2 sensor is bad. I was using it to try and get some values on the a/f ratio and other possible problems.

I'm reading the values directly from the select monitor.

You should be able to tap into the sensor line with a DVM and get the values.

02 sensor voltages are a sudden jump between rich and lean. The line graph starts out smoothly, drops quickly down to almost nothing and then smooths out straight again

Here is an idea, the voltages are not exactly right but pretty close to what you should see.
mvolt----ratio
1000-----2
950------7
800-----14.4
500-----14.6
200-----14.8
100-----15
50------18
0------20

In other words, ultra rich is 1 volt and incredibly lean is .02 volt. A PERFECT stoich mix should produce .5 volts.

02 sensors ARE a wear item with a life between 30k and 50k. Even if the sensor is still working they become slow to react as they get old. Dirt clogging the outside of the sensor can also greatly effect it. Realize the sensor is actually double sided! The outside air and inside air is compared and a voltage is created from that comparison. Thats why they dont need elevation calibration!

The sensor is only acurate when its between 680 and 1650 fahrenheit.

edit: Found these two great images and a PDF, read the second page
http://www.delphi.com/pdf/intellek/oss_sensor.pdf




This second one shows that 12.8 (slight rich) is best for power while 15.3 (lean) is best for economy

Two questions.

Are our sensors wide band or narrow band?

Second question. that second graph you posted ciper, is there any explanation behind it? You're going to make the most pressure & temperature in a cylinder at stiochometric. Must be a timing and fuel issue, because more fuel does create a faster burn.....

I heard that O2 sensors were either on or off. When they get to a certain level they produce a signal and when the level falls they stop producing a signal. This didn't sound true to me but I'd like to know how they work in our car at leaste.

Thanks, Mike

I've got a question that seems to fall into this topic.

I'm uncertain if possibly my O2 sensor is bad. (or I guess maybe dirty, I'll have to check that).

A few weeks ago I installed an A/F gauge, and it always seemed to work properly (max rich at high throttle settings, max lean when off the throttle, jumping back and forth when at constant throttle).

A couple days ago however the guage went very lean (in fact it didn't even light up unless I was on it hard, and then it would only get up to stoich at best. Now, at first this worried me, because I was worried the motor was actually running that lean and I was having a fueling problem. I was very gentle with it, until I happened to be stopped with the windows down, and blipped the throttle and immediately smelled gas. It has happened often since, but never before. Now, here's my hypothesis: the O2 sensor is reading low, so the ECU is adjusting mixture to max rich to attempt to bring it into proper ranges, but the sensor won't given a proper reading. Make sense?

Thanks

Josh - They are narrow band. All the discussion so far in this thread is about narrow band sensors.

The second graph ciper posted is typical of most cars, actually; internal combustion engines tend to make the best power a little richer than stoichiometric. The combustion pressures and temperatures typically peak at a ratio around 13. I don't know the reason, but you might be right with your guess about timing of the burn. Another thought is that maybe not all the fuel gets burned during the power stroke due to inefficiencies in the design, so putting a little more fuel in there could help.

They get the best fuel economy running a bit lean, which makes sense. This is the idea behind lean cruise. Stoichiometric is just the best ratio for catalytic converters, and so in turn it's the best for emissions.

Mike - If you look at the first graph ciper posted, you'll see that it pretty much is either on or off. The area in between is very small. Almost all (if not all) ECUs treat the signal as a binary one. This is partly just because there's such a small area in between, but also partly to make the ECU resistant to small voltage offsets.

Ryan - It sounds like your hypothesis is correct. Either your sensor is gunked up or you have a really bad ground path for it. Either of those could cause the reading to be too lean.

Just something I read about the other day about sensors getting carbon'd up.

You can create a vacuum leak and rev the engine around 2000 rpm for a minute or two. This will cause a lean condition in the cylinder and temp should go up, which should help burn off extra carbon. It'd probably work with the cat's as well.

Whether this works or not.....got no idea. I may try it with the select monitor hooked up to monitor O2, temp, and timing readings.

If you do it while the engine's cold or with the oxygen sensor harness disconnected that could work... If the engine's warm with the sensor plugged in it will try to reach stoichiometric ratios again, assuming you're trying to do this with the car stationary.

I've never heard of trying to burn off carbon deposits this way. Interesting...

sitting at idle though, or in neutral, you'd be in open loop correct?

Doesn't really matter what the O2 sensor is doing then.

Also check out the bottom of my thread over on nasioc
http://forums.nasioc.com/forums/showthr ... did=390715

This is from an e-mail I got from Bosch a while back.

MinV MaxV A/F ratio
0.0 0.1 17.0:1
0.1 0.2 16.0:1
0.2 0.3 15.5:1
0.3 0.4 15.0:1
0.4 0.5 14.7:1
0.5 0.6 14.6:1
0.6 0.7 14.5:1
0.7 0.8 14.2:1
0.8 0.9 13.2:1
0.9 1.0 12.5:1

These values are at 1200 dergeesF. Similar readings will be found from 800-1400 degreesF. As temps varies the O2 voltage will vary also, for example:

@ 750 degrees a V of 0.9 will indicate a A/F ratio of 12.4:1
@ 1500 degrees a V of 0.9 will indicate a A/F ratio of 14.0:1

When idling the ECU should be running closed loop. It's supposed to use open loop only when the throttle is fairly wide open, under boost, and when the engine is cold. Maybe also any time the engine speed is high.

As I posted in another thread ( viewtopic.php?t=1402 ) I am pretty sure the oxygen sensor reading's almost always at least looked at by the ECU.

I played around with things tonight. Pulling the brake booster hose and keeping engine going results in an extremely lean condition on the O2 sensor reading. This results in a correction ratio that sky rockets.

You would have to pull the plug on the O2 sensor and then introduce a vacuum leak to try and run really lean. There was no knock or other issues that the select monitor read.

A/F gauges are really just a primitive tool that will tell you if you were to fall into lean conditions under max boost or something similar that is really bad. Otherwise, you pretty much can just ignore it. And when decelerating it is usual for it to go so lean that nothing even lights up.