How do you know if 02 sensor is really bad

[steviee7]

Like the subject asks. I'm wondering (since I don't know how old it is) if I should replace the 02 sensor.

My car is kind of driving to where if I accelerate slowly, the car feels like it accels in different stages. I can almost feel a sweep in good power to not so good power. As if someone is lightly pushing on and off the accelerator like evey second.

If I disconnect the 02 sensor it goes away.

[88911coupe]

This might be due to a worn spot on the air flow meter track. Do a search since there's some good threads on how to remove it and clean it up...not to say the O2 sensor is not bad either.

[steviee7]

I thought of that after reading about the cleaning process (I haven't yet and I'd like to some day)...But I thought that that can't be the culprit since it happens through out the entire rpm range from idle all the way up. The fact that it changes with the 02 disconnected makes me wonder... hmmm.

[nhromyak]

Hmmm I have this same issue. I do know that the O2 sensors get lazy as they get older. Basically, an O2 sensor is a meter that oscillates and only knows if the mixture is rich or lean. The computer measures this oscillation and adjusts the mixture based on a few other factors. (A wideband O2 sensor is different).

Anyway, I am pretty sure my O2 sensor is too old. I always thought my issue was my AFM being out of adjustment / old spring / CO not quite right.

I will try disconnecting my O2 sensor and see if I too get the pulsing acceleration to go away.

IIRC - the computer will go into a basic mode, of sorts, and use base timing and settings without an O2 sensor.

It sure would be nice to have G-tech or something to determine if the car accelerates faster with or without the O2 sensor connected.

[Por_sha911]

Originally posted by 88911coupe
This might be due to a worn spot on the air flow meter track. Do a search since there's some good threads on how to remove it and clean it up...not to say the O2 sensor is not bad either.

I am a big fan of the search button but I can't find anything on how to clean the AFM track. Can someone please point me in the right direction?

[nhromyak]

http://frwilk.com/944dme/

I don't know about CLEANING it. Basically, you bend the wipers so they use a different (worn) track on the sweeping area that measures voltage as the air passes into the engine.

This has made no difference for me.

Good luck.

[imcarthur]

Hey, the link is back! His AFM page was down for several months. But I gotta agree. Moving the wiper made no perceivable difference here either. But it was cool to try.

Ian

[steviee7]

Well I'm guessing that the AFM thing works for some but I think I might investigate the o2 sensor a bit more. Could this symtom be from mis-adjusted CO2 readings as well? The car was fine I didn't touch a thing.

I own a A/F meter it's just that it's in my other car and removing it and installing it in the 911 is time consuming (for me) I'm not sure where the best place to tap into the wires are. Do the wires show up in the dash or just go directly to the ECU under the seat. Would it be easier to tap the wires from where the o2 disconnects in the engine bay? If it's easy I'll do it.

[jabb]

There is an OHM range that the O2 sensor should be putting out. Not sure what it is I tried seraching but did not find the range. I believe the O2 range might be published in the Bently Manual. I am not near my manual maybe someone could look up the OHM range for the O2 sensor.

[imcarthur]

[jabb]

imcarthur


Thanks for posting.....

[steviee7]

nice test tool...
That's real interesting why the engine would run lean if the oil filler cap is loose. (that's for another discussion)
I've noticed the rubber insert inside the filler cap is not very soft but hard. It could possibly be not really making a great seal. I don't think it's related to my symtons though.
thanks for the diagram imcarther