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GA16DE
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606 Posts
Discussion Starter #1
Hi
I am using a narrow band O2 sensor and a dmm to aproximately tune mi a/f ratio
Under some circumstances the reading is negative (- 0.1 / -0.2)
Sensor reads at idle +0.6 / +0.7 and my dmm isn't the cheapest one
Is this possible?
Thanks in advnce
 

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Proud owner of a GA16i
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508 Posts
to tune a/f, you must have a wide band O2 sensor. Narrow band means it can only read at one point. So is your dmm reading in voltage or does it actually output a a/f reading? dumb question right? So please add some units. Good luck in tuning your a/f ratio.
 

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GA16DE
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606 Posts
Discussion Starter #3
I am conscious narrow band measures exactly part of the scale (center), and the rest varies with temp mainly (higher than 14.7:1 a/f ratios specially)
I can't afford a wide band sensor at the moment, and have a couple narrow band sensors around
Thing is, I don't want to run lean, and I can see it with my narrow band unit
Thanks anyway
 

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GA16DE
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606 Posts
Discussion Starter #5
narrow band O2 sensors range from 0.1 to 1.0 volts dc output, at working temperature for the O2 molecules to create the voltage bla bla bla...
0.4 to 0.6 volts is the stochiometric ratio 14.7 parts of air to 1 part of fuel (weight)
I just want to see it's over 0.6 volts, preferably around 0.9 volts to be sure it's not running lean
And I'm aware it varies with the exhaust temps
 

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0.450 V is stoich 14.7

If you have fuel injection then you should read it going back and forth between .2ish and .6ish Except for WOT then it just goes rich...or should anyhow. And as we all know the sensor HAS to be warmed up.
 

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Proud owner of a GA16i
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ok, you're reading volts from your dmm, that's what I wasn't clear about. So do you have an induction coil or do you hook up the dmm directly to the sensor and ground? What circumstances cause your dmm to go negative?
 

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GA16DE
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606 Posts
Discussion Starter #8
Thats my question, it's connected directly to the O2 sensor
As much as I know it should read positive values only...
Thanks for answering
 

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velardejose said:
Thats my question, it's connected directly to the O2 sensor
As much as I know it should read positive values only...
Thanks for answering
yes it should only read positive . I find this very odd and can't think of a reason for it to show negative. Only time you should show negative in DC is if you're reading AC or if polarity is crossed.
 

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Proud owner of a GA16i
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yeah, so far, the only thing I could think of is a bad connection through your dmm. You said that it reads +0.6 to 0.7 volts @ idle. What does your dmm read at 2000 rpm? 3000? 4000? when exactly does the voltage drop to -0.1? is it erratic? does voltage jump, or ramp down to -0.1/-0.2 when it happens?
 

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velardejose said:
I am conscious narrow band measures exactly part of the scale (center), and the rest varies with temp mainly (higher than 14.7:1 a/f ratios specially)
I can't afford a wide band sensor at the moment, and have a couple narrow band sensors around
Thing is, I don't want to run lean, and I can see it with my narrow band unit
Thanks anyway
www.DIY-WB.com

Yes-- it works!
 

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GA16DE
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606 Posts
Discussion Starter #12
Interesting data, thanks
I'll read it carefully...
 

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GA16DE
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606 Posts
Discussion Starter #13
It still has negative voltage at idle (-0.1 volt constant)
When accelerating climbs to 0.7 and stays there
I discovered a black spot in the base of the welded nut where the o2 sensor is installed, maybe it's sucking air...
I'll have it corrected and tell you what happens
 
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