O2 Sensor functioning? Paranoia?

KatoKato · 07-10-2005, 06:21 AM

Hi All. Just finished my premuffler install on the 86' 911.

I put in a new O2 sensor and as I am a newbie I was wondering if there were any "tell-tale" signs that the sensor is working.

The only evidence so far (I think) is that when cold the engine idles @ 1100 rpm and once warm idles just over 800 rpm.

Are there any other ways to tell if it's working (or not?)

Thanks in advance,
Kato

cgarr · cgarr's Garage

If you unplug it, take a volt reading from it when hot, I think if your mixture is correct it should read somewhere from .4 to .8 volts? somewhere there is a chart/scale that shows this on this board. I dont know if this proves its working but thats how I checked my mixture at idle.

Craig

gost · gost's Garage

Kato, I just installed my pre-mufffler and muffler bypass from Fabspeed and installed a universal O2 sensor manuf by Denso and Craig is right as far as checking it. Also if it runs great through the range of operation then it should be functioning properly as well. My system seems to be perfect so far. What system did you put in and are you using a muffler?
Whose O2 sensor did you install?

Gost

KatoKato · 07-11-2005, 04:02 AM

Quote:

Originally posted by gost
Kato, I just installed my pre-mufffler and muffler bypass from Fabspeed and installed a universal O2 sensor manuf by Denso and Craig is right as far as checking it. Also if it runs great through the range of operation then it should be functioning properly as well. My system seems to be perfect so far. What system did you put in and are you using a muffler? Whose O2 sensor did you install?

Gost

It's a stock setup except I switched out the cat. with a Dansk (non-stainless) pre-muffler. I used a 'Walker' OEM O2 sensor.

As far as I can tell things are running normally through the range of operation. No issues like the ones described by another member (this is my second premuffler thread):

Pre-Muffler Install Has Begun!

The chip is next.

One question for you regarding the re-tightening of bolts after install. (Danskman must be away from his computer because I've tried PMing him regarding this)

Should I re-tighten the bolts after my first long drive and then after about 200 miles? Or is just one of these necessary. Those bolts are in their really tight.

Cheers,
Kato

KatoKato · 07-11-2005, 04:05 AM

Quote:

Originally posted by cgarr
If you unplug it, take a volt reading from it when hot, I think if your mixture is correct it should read somewhere from .4 to .8 volts? somewhere there is a chart/scale that shows this on this board. I dont know if this proves its working but thats how I checked my mixture at idle.

Craig

Cool I might try that. Do I check by sticking my multi into those two "round" ports at the connector.
_
. .

I don't have a pic. The dash and dots are my best try!

rick-l · 07-11-2005, 08:39 AM

Quote:

Originally posted by cgarr
If you unplug it, take a volt reading from it when hot, I think if your mixture is correct it should read somewhere from .4 to .8 volts?
Craig

that's not the way it works. The oxygen sensor puts out about 2 volts when it is in a rich (no oxygen) environment and < .5 when it is in a lean environment (not enough fuel to react with all the oxygen). The output is a step (very steep slope) between rich and lean. The computer tries to maintain optimal (lambda) by switching the mixture between rich and lean.

This is called a bang bang control system, kind of like the thermostat in your house. Too cold, add heat (turn on furnace). Too hot turn it off. Do this fast enough and you maintain a reasonably steady temperature.

If you have a high impedance voltmeter you should be able to monitor the sensor output (+ lead on the sensor - to ground) and see it switch but I have never done so.

fireant911 · 07-11-2005, 09:23 AM

My oxygen sensor puts out between 0.1 and 0.9 volts during normal operation though it is hard to truly determine the values since the 'brain' is continuously adjusting the mixture. As my memory serves me 0.45 volts is the stoichometric value (14.7 AFR). I have installed Westash A/F gauge to monitor the lambda activity. Unfortunately I have performed a great amount of Oxygen Sensor testing since this I previously had an inoperable lambda system.