No Reading On O2 Sensor

[grb008]

I thought my O2 sensor was bad so replaced it as it was reading at idle almost no voltage. Turns out nothing was wrong with the original O2 sensor when I put a torch to it. It got red hot and showed voltage.

I've only tested it at idle, and revving engine from idle when all warmed up. Is it possible it just isn't hot enough to read yet, or do I have some huge exhaust leak that I'm not seeing.

My next step is to make sure the heater wires are working. I think they only turn on when car is running so will check those. Going to check for exhaust leak, but should i just drive the car and warm it up real good then see if there is voltage.

[dannobee]

O2 sensors don't have output until they get warm, either by the exhaust or the heater (if equipped). It certainly won't have enough heat to produce voltage on a cold start. You'll need to drive it before the O2 sensor comes online.

[grb008]

Ill try to drive and see what happens after I check the heater wires.

[Schulisco]

O2 sensors require a temperature of at least 350°C/660°F to work properly. Which car/o2 sensor do you have?

On SCs the unheated O2 sensors were factory standard. If you remove the catalytic converter the O2 sensor can cool down that much that no signal is emitted any more when engine is idling, e.g. at traffic lights, because the catalyst is also hot and heats the O2 sensor sitting right before it.

You can upgrade to the O2 sensors of the 3.2 Carreras, which is a heated one. You can take the supply for it's heater from the 3 fuse panel in the engine compartment that powers the O2 sensor only when ignition is on.

Refer to this information provided from Hella about O2 sensors:
https://www.hella.com/techworld/ae/Technical/Sensors-and-actuators/Test-lambda-sensor-4379/

Also not to forget not to solder the O2 sensor cables! They're Nernst sesnors, which means that they need an Oxygen reference input from outside the sensor. They take it from the cable, it's only a few atoms they need...but if they cannot any more they won't work! If you soldered them already, you can try to make a tiny gap in the cables insulation close to the sensor to reactivate it...

And also not to forget to mention that O2 sensors are sensible to mechanical shocks. So handle them very carefully while unpacking and (re-)mounting!

Thomas

[grb008]

Its 84 3.2 but has an 87 engine. I replaced the O2 sensor with the bosch one that has the big rubber single wire boot and the 2 heater wires. I tested the heater wires and its giving over 13v with the car running. When I came back from a short 15 minute drive it was still reading low (car temp showed about 170), revved the engine and it went to only about 200 mv. Car doesn't seem that lean though. Plugging in the O2 sensor at idle raises the idle about 200 rpm, unplugging it reduces the rpm back to normal 850-900 idle.

[Schulisco]

First and foremost: Check the mixture on a certified gas tester to prove that it runs not too lean.
While cruising with lower and medium speeds the O2 sensor must show a signal oscillating between 0,1 and 0,9 volts.
Supposimg that your sensor is good and the engine reacts as described I guess it runs too lean.

[grb008]

Im waiting to borrow a co tester, I'm also getting an unmolested AFM. I've replaced lots of things needing care for an almost 40 year old car. New fuel lines, new injectors, new intake gaskets, fixed all vacuum leaks, new spark plugs, cap, rotor, wires, replaced autothority chip with SW. Cgecked all valves and fixed 2 that were beyond loose.