3.2 oxygen sensor

[993.986.]

How does one know if the O2 sensor is bad/failing? To my knowledge it has never been replaced. The car is an 87 Targa with 87K miles.

[Joe Bob]

Smog shops can test them....they run anywhere from 60-100+ bucks.

[993.986.]

As bad as this may sound to some, I don't care about the smog testing(not required here), I just thought it might need replacement after 87K miles. The car runs pretty good actually, but how would I know if would run better with a new sensor?

[Joe Bob]

You don't....if it came with one it needs one on a regular basis. Mine was toast after a year. BTW, Porsches run better when tuned with an exhaust gas tester. IF one of the sensors (likE the 02) is bad, the car can run overly rich fouling plugs and reducing performance and gas mileage OR run lean and burn a valve....

[tbitz]

They are easy to test. You need a volt meter (digital, because they have a high impedance).

Connect the positive lead to the sensor wire and the negative to ground. With the engine running the voltage should be bouncing around 0.3v to 0.7v when the mixture is ideal. If it is always reading 0 volts then it is dead.

Sensor has to be hot to read properly, so idling may not be hot enough. If it reads anything above 0.1v at idle it is most likely working.

[ischmitz]

The oxygen sensor needs to have a response time of about 100mS between rich and lean condition. First their response time slows way down due to contamination of the zirconia element. So even if you see the 0.4 volts output the thing might be over the edge already.

Serach google. There are some in the car and on the bench tests where you heat the thing up with a propane torch and watch the time it takes for the signal to change.

Ingo

[ischmitz]

http://www.interro.com/techoxy.html

read here. In the car you have to snap the throttle to see the response time.

ingo

[Harold_89_911]

You can get a Analog to Digital converter pretty cheap and hook it up to a laptop so you can check your O2 probe while driving. I got one from DataQ (dataq.com) for about $25 and that included the software. I have been struggling with my 89 Saab 900 and compared the O2 response during driving to that of my 91 Saab 900. The car felt like it was driving rich but the data helped me to eliminate fuel delivery as a problem. I'm back to checking ignition now. Some of the examples of the data I got:

[Lorenfb]

On the 3.2 engine, you can usually tell how well the O2 sensor is functioning
by how the engine reacts when running closed-loop (O2 hooked-up). The idle
will hunt/oscillate about 25 to 50 RPM. Disconnecting it results in an increase
in RPM and no hunting.

The key, though, is how it affects the CO and HC levels once connected
versus disconnected, i.e. It will "pull" a CO level of 1% after the CAT to
less than .25%. The response time of 3.2 O2s is less critical than for later
Porsches. The 3.2 O2s either work (produce a varying voltage) or they
don't.

[Steve W]

Nice pics, here's some more from Bosch:

[993.986.]

I've been meaning to get a volt meter anyway as I don't have one. I'll search google, but I don't have a propane torch either (hey, I'm proud to have crow's foot wrenches and a torque wrench!). I'm starting to think I may just replace it and see if it makes a difference. Any suggestions for what to look for in a volt meter (digital). Thanks

[scottb]

Is it possible? Steve W and Loren in the same thread, and no discussion about the effectiveness of chips? Do we have detente?

[993.986.]

I'm so proud it happened on my thread

[ischmitz]

Harold,

what you show is nice data. The times the O2 sensor crosses between low and high is what is important. Yours (at 70 mph) seems fine.

Ingo