wondering if anybody can tell me how to read the O2 sensor's output while the car is running. My car failed emissions again yesterday and was running really rich. I re-readjusted the TPS and would like to see if that had any effect on the mixture before I go back to the testing station and fork over more $$$
So, how/where to read the sensor's output and what should it be at idle/ and 25 MPH ( +/- 2000 RPM)

BTW, it's a stock (except gutted pre-cats) 86 GXL.

Thanks,
Cory

 

You can use a multimeter to probe the wire coming off it, or probe the O2 sensor wire that feeds into the ecu.

I don't know what readings to expect, but I'm sure someone else does.

 

do you have a safc? you can use that!!!!

 

I think you probe the O2 sensor from the wire and ground the other side.

Idle should be around .5
On accelerate around .7
on decelerate around .3

not sure....this is from memory.
It's listed in the FSM at www.fc3s.org

 

The 02 sensor has no effect on the ECU at idle. Can you tell us more about the emission test? Was it a two part test, one at idle and the other with a load perhaps??? Do you still have your airpump attached along with the air control valve. And do you still have a catalytic converter? And did you change spark plugs, air filter, and set the timing prior to the test?? Have you been messing with the rich/lean screw? Anyway, the 02 sensor wire at the ECU is pin 2D. Thats on the middle plug, and counting from the right to your left as you look into the ECU, its the bottom row, second one over from the right. If you trace the wire into the harness it will run inside a shielded cable, which in turn should have a ground on it. I have found that on a stock car, with all parts in place and not removed, you'll see either a minus dc voltage at idle or a minimal figure like .010 due to the PORT AIR mixing just prior to the o2 sensor. At cruise in forth or fifth,say 60mph, I see figures on either side of .4v as the ECU tries to maintain stoich. Figures that jump continuously and at a rapid rate on either side of .4v. At wide open throttle I see .7 to .75v. Thats on a N/A car. One thing I do notice, is that when I disable my airpump or acv, that the reading will be something like .6 or .7v at idle. Thats due to no air from the air pump going to the PORT AIR just in front of the o2 sensor. Also if the water temp switch on the left bottom of the radiator is off or broken, there will be no air to the proper passages of the acv because the RELIEF SOLENOID is disabled meaning the air that goes into the acv from the air pump is dumped straight overboard. This site http://www.autometer.com/hp/index.html under TECH TIPS AND FAQ gives a good description of the voltage readings and the definition of stoichometer