O2 sensor voltage readings

[Steve]

Hi,

Has anybody checked or know what the readings should be from a HEALTHY O2 sensor should be. I would like to know that state of mine.

I was looking at mine, it reads 0.00V at idle, at cruise it jumps erratically between 0.00V and 0.8~V quite rapidly. I havent been game enough to check other than cruise and idle, as its a bit distracting trying to read the powerfc display whilst driving.

My car is an R33 GTS, but if anybody has any info for any model skyline, please post up, either personal experience or workshop manuals, all is good.

Cheers

Steve

[browny]

AFAIK a normally operating O2 sensor will rapidly flick between 0-1V.

[JasonO]

Steve,

From memory.......Mine used to swing between 0V and 0.89V at idle, and on cruise.

It's a narrow band sensor, so it won't really have a good resolution and it will mostly show either all the way rich or lean, only stabilising when the mixture is stoich.

(not sure if I'm making the best sense with that description though, but it is nearly 4am :coffee: )

It should defo swing at idle though, so somethings not right.........

[blind_elk]

The purpose of the O2 sensor is to enable the ECU to maintain a stoichiometric A/F ratio (14.7:1). Unfortunately it is a reactive system ie the ECU has to see the AFR go off stoichiometric before it will make any adjustment to the fuelling. The reason it fluctuates so rapidly is that the voltage output of the O2 sensor changes rapidly around the stoichiometric centre, and less rapidly further away from stoichiometric centre (the shape of the curve is similar to a heartbeat on a heart monitor).

If your O2 sensor is saying 0V at idle, it might be that the AFC is programmed not to monitor AFR at idle. At cruise (and it can really only work at constant throttle settings), the O2 sensor voltage will fluctuate between 0V and 1V as the ECU attempts to adjust the fuelling to achieve stoichiometric AFR.

What your O2 sensor is doing seems to be exactly what its supposed to do.

[JasonO]

If your O2 sensor is saying 0V at idle, it might be that the AFC is programmed not  to monitor AFR at idle.

What your O2 sensor is doing seems to be exactly what its supposed to do.

Errr, I'm running a PFC the same as Steve, so one of them has to be doing the wrong thing ......

.....Now I'm just confused

[Steve]

I am a bit confused too, as I checked the voltage under the sensor check option on the power fc, so it hasnt been molested by the ecu, it just reports what is sees.

Also, 0.0V is reported on decel, which I would have thought it would be seeing max O2, as it cuts fuel on decel. It definately isnt lean at idle, where it also shows 0.0V, I had to pump a fair bit in to get it nice with the cams - so it appears to be wrong somewhere.

Maybe I will have to just bite the bullet and get a new oxy sensor. I hate spending money on things unless I am sure I need to:)

[Cubes]

Quite a while back I put mine in to O2 sensor diag mode.

It also flicked on and off at idle and cruise.

Under normal acceleration it was constantly flicking. only when it started making 2psi+ of boost is when it would stay off.

I am also fairly sure that it would stay off upon deceleration. Pitty I can't check as the car is in getting sprayed.

Steve,

I'm getting around 500km's to a tank of juice so if you want you can try my o2 sensor, car is current in bits at the spray painters so it isn't going anywhere. Providing the plug is the same which I am sure they are.

Last I priced O2 sensors are up around $280.

I think the preheat is stuffed on mine though as it runs a little strange when cold.

[Steve]

Joel, that would be awesome, can you pm me when and where I could catch up?

Cheers

[Busky2k]

Hi Steve.

My car sits just below stoich on idle. So the O2 readout sits on about 0.05V to the flickering between 0.1-0.8V. I can dial in less or more fuel with the SAFC and it will fall to near 0 or sit at above 0.8V constantly, until the ECU relearns this and leans/richens it out again, although it does take some time. Its strange how yours doesnt change. Have u tried dialing in more fuel and seeing the result?

At exactly 14.7 AFR, the O2 voltages will fluctuate rapidly between 0.1-0.8V which shows that the O2 sensor is functioning properly. As a O2 sensor wears out, the rate of flux decreases to the point where it becomes very unresponsive. Nissan state that the voltage must flucuate at least 5 times per 10 seconds or the sensor is worn. A sensor which gives a constant value despite a change in AFR is stuffed.

On decel you should get 0V because the ECU cuts fuel completely. I get stoich AFR right upto about 4psi.

Btw I've seen that it takes about 45-60 seconds for the O2 to become responsive from a cold startup. Thats on a sensor thats done 115,000ks....

[Steve]

Thanks Busky, makes sense. And sounds like the O2 sensor isnt stuffed then, which is a good thing.

I will recheck what its doing again and see if I cant make sense of it.

Cheers

[x2shy]

If you disconnect the o2 sensor. The car won't rev past 2.5k. (don't ask me how I know.)

So I would assume that ecu doesn't care about 02 sensor voltages prior to this point?

[Busky2k]

No. Most likely in this case, the ECU goes into 'limp home mode' (open loop) and will leave the rev limit at 2.5k. Pull the plug on the AFM and the same thing will happen.

The ECU utilizes the O2 sensor in every situation except for when the RPM is over 4000.