unirig

Until I figure out why, my '81 SC runs better with the (new) O2 sensor unplugged. However, I was playing with the mixture and am paranoid about running it too lean. Does anyone know the output voltage the (unplugged) O2 sensor should show with the correct mixture? Thanks. Don

Lorenfb

The ideal mixture would be indicated by .50 to .60 volts at the O2 sensor
with it disconnected.

art

You can buy a mixture meter which monitors voltage at the O2 sensor. These are cheap, and then you will always know what is going on.

unirig

Thanks Loren and Art. I had it be set too rich (above .90V).

Noel

Tell me more about how you guys measure the output voltage of a oxygen sensor. How is this done? I have a 1980SC and think this would be helpful in setting the mixture.

Thanks,

Noel

art

Have you seen the ads for mixture meters that have LED graphs showing rich or lean?

They are only about $30.00 and are just dedicated voltmeters for the low voltage range that an 02 sensor develops when hot.

I know JC whitney has them, and I'm sure plenty of others. SDS has one on their site. You will need to splice it into the wiring from the sensor, but it is no big deal.

You will like being able to monitor the mixture constantly.

Noel

Thanks Art.

jetskied

Don't measure the voltage at the o2. This may be unreliable due to the fact you suspect a o2 problem and the sensor has to be hot 600 degrees. The best way is to get a gas analyzer, but its a costly tool (guson $200). Many people set there Co by unplugging the the frequency valve and measuring that plug with a dwell meter in the 4cyclinder cycle. I'm not sure what is the specs for a 911, but I know people do it for the 930s.

art

Go to your local parts store and buy the cheapest o2 sensor they have and replace yours if you suspect it. They are all the same, you just have to change wiring. Wiring can be a hassle since the wires are some kind of high grade stainless that does not solder easily. Acid flux required.

I think the cheap ones are around $30.00 or so. Just ask for whatever mass market car you can think of. The more they make the cheaper they are. You should be able to ask the parts person what is the lowest priced one they have.

art

I think I have seen the measurement method and values needed for the freq valve on various sites around the net, so you should be able to find it.

Lorenfb

"Many people set there Co by unplugging the the frequency valve and measuring that plug with a dwell meter in the 4cyclinder cycle."

You can't properly set the CO with frequency valve disconnected because disconnecting
the valve forces the fuel distributor into the full lean mode. If the CO is set with this
condition, the CO will be very rich when the freq valve is re-connected.

One method is to set the CO, with everything hooked-up except the O2 sensor,
to about 1.0 to1.5% using a gas analyzer and later hook-up the sensor. Another
method uses a dwell meter, with everything hooked-up, to monitor the duty cycle of
the freq valve and set the mixture to a value which results in a 50% duty cycle.