I've been trying to figure out why my new O2 sensor isn't showing the correct voltages ... after getting a replacement from FCP Groton (these guys are very helpful) to replace what I thought was a bad sensor they had sent me... I clip leaded the new one in and it did exactly the same thing my first new one was doing!

2 new O2 sensors that were both dysfunctional in the same way? I don't think so ... something else is wrong...

So after some amount of research on O2 sensors and fuel injection I retested my O2 sensor and it is still doing the same thing.... starting out at 500 mV then slowly dropping to 30mV - 50 mV and just resting there. Spiking up to 600 mV quickly and fluctuating a bit when I push the throttle open.... then resting at 40mV or 50mV when it drops back to idle.

I do have good voltage and ground going to the heater of the sensor, and there's about 5.7 ohms resistance on the heater when cold and 11.5 ohms when hot - this seems a little off from Bentley's specs but still close enough I think. I'm using a good Fluke Digital multimeter (not mine unfortunately).

so I was messing around with it a bit and I decided to try to send more fuel to the combustion to see what would happen ... so I pulled the vacuum line off of the fuel pressure regulator (thinking this would send more fuel to injectors?) ... no change.

since I didn't really know what I was doing I figured maybe I needed to close the vacuum line that normally attached to the regulator rather than just leave it sucking air, so I put my thumb over the hole and it definitely had vacuum as it sucked part of my thumb onto itself and closed itself off

the interesting thing is that at that point the O2 sensor started functioning normally! switching quickly between a high and low voltage (700 mV-850 mv on the high end and 80-250 mV on the low end). Just like it was supposed to all along.

so I'm stumped ... I took my thumb off the vacuum line and the sensor dropped to 50 mV where it then stayed until I closed the vacuum line again!

So I'm thinking I've got a good sensor but something weird is happening on the vacuum for the intake/injection side of things????

vacuum should have no effect on voltage, right ?????

Any theories out there?

I just learned about O2 sensors in the exhaust stream and their voltage specifications... now I have to figure out how that relates to vacuum pressure?
soon I'll be working for Ford or something... well probably not!

jack

Columbus, Ohio
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Bad Blue, '86 245, 244,000 mi.