Can autometer a/f gauge tell me if o2 sensor is dead??

robbo185

robbo185

New Member
Apr 6, 2005
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I have been having problems with my car running very rich at idle lately. At idle it is around 11.7a/f and while driving its around 14.7.

While driving my a/f gauge used to do the normal light show. However, lately even at idle, it just sits in the same spot and only moves when i blow off after i shift. Since the light only sits in one spot at idle...would this show that my o2 sensor is about dead? Engine has about 85K on it and im sure its original o2 sensor.

fuel mods are 550cc injectors, aeromotive afpr at 23psi with vac attached, j-tube is bypassed, walbro 255 pump.

Today i replaced my plugs and put the tps into spec.

Would a bad o2 sensor be at fault for the running rich at idle?
 
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dbsupra90

toonar
Apr 1, 2005
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yeah its possible the 02 is dead. they are designed to go rich as a failsafe. might want to check for boost leaks just to be sure and possibly check Vf voltage to see what the ecu is doing.
 
madsupra88

madsupra88

BoOoOoST
Sep 17, 2005
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Dead o2 possible, and or the gauge is not getting a signal/weak signal. the the wire leading to your o2 sensor.
 
Last edited:
Clifton

Clifton

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Apr 5, 2005
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tookwik4u89 said:
The voltage should kinda sweep up and down between .1 & .9 volts at idle once its warm. If it stays in one spot its cashed.
Click to expand...

Don't think so, .4 and .5 maybe. .9 would be as rich as it could get and .1, it wouldn't be able to run.
 
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Suprawannabe

meh... im lazy
Oct 27, 2005
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Denver, CO
Clifton said:
Don't think so, .4 and .5 maybe. .9 would be as rich as it could get and .1, it wouldn't be able to run.
Click to expand...

Yes they do, but those gauges are only good for a light show since a good working 02 will switch back and forth 10 times a sec and will not be accurately shown through them.
 
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Suprawannabe

meh... im lazy
Oct 27, 2005
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Denver, CO
tookwik4u89 said:
I do it almost daily, on Toyotas, you may not see full sweep from 1-9, but 4-5 is not normally what I see on a good one.
Click to expand...

Well yeah not 1 exactly but around .1XX,2XX - .7XX,.8XX on a brand new sensor. The older they get the sweep gets smaller and sweep/sec get lower.
 
Clifton

Clifton

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Apr 5, 2005
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Suprawannabe said:
Yes with a scope, you have to measure in milliseconds not real time with a meter.
Click to expand...

Being that the ecu just measures the voltage, same as with a dvm, there is no need to use a scope to measure in miliseconds. If you just measure the voltage it will be .4-.5 at stoich, .8-.9 at WOT.
 
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Suprawannabe

meh... im lazy
Oct 27, 2005
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Denver, CO
Clifton said:
Being that the ecu just measures the voltage, same as with a dvm, there is no need to use a scope to measure in miliseconds. If you just measure the voltage it will be .4-.5 at stoich, .8-.9 at WOT.
Click to expand...


Yes your right the ECU measures the voltage but it can process the info REALLY quickly and understand it. A DMM can only sow you bits of information. There is need for a scope if you want to slow this info down to get a real accurate reading. Yes .4-.5 is stoich, .8-.9 is WOT. We were talking about how a good performing O2 operates. The whole point of it going from rich to lean is for emissions, the oxidizing part of the catalyst does not remove CO and HC very well with mixtures that are rich and NOx reduction does not work well when lean. So by having your O2 going from rich to lean allows oxidation and reduction of NOx.
 
Clifton

Clifton

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Apr 5, 2005
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If you are going from .1 to .9 at idle or anywere you have a problem. If it is varrying the whole range of voltage it won't know were it should be. Reset an ecu and check it, mine was rich everytime (checked with LM1 too) for a few days before settling downto stoich (.45 with a narrow band). Lm1's can produce 0-1v for narrow band ecus too. They put out the correct v, not .1-.9at stoich as you think it should be.
 
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Suprawannabe

meh... im lazy
Oct 27, 2005
122
0
0
Denver, CO
Clifton said:
If you are going from .1 to .9 at idle or anywere you have a problem. If it is varrying the whole range of voltage it won't know were it should be. Reset an ecu and check it, mine was rich everytime (checked with LM1 too) for a few days before settling downto stoich (.45 with a narrow band). Lm1's can produce 0-1v for narrow band ecus too. They put out the correct v, not .1-.9at stoich as you think it should be.
Click to expand...

Dont listen to him, he has no clue what he is talking about.


Go to your diagnostic box,fully warm up your car and hook up your voltmeter to Te1 and E1. Rev the motor to 2500 RPM's. Count how many times your meter fluctuates in 10 sec. Eight or more is considered good, any less you want to check your voltage at VF1 and E1. If you have more than one volt replace the O2 if you have less that one volt check for codes..
 
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