Antony.

I recently got a high but passing CO% reading during a smog test. After reading up on the emissions system and seeing that the O sensor plays a large part I checked the connections and think they were loose during the test.

Would a disconnected O sensor cause the readings to go from 0.01/0.03 at the last test to 0.81(15mph) and 0.65(25mph)?

If so, can I test the Oxygen sensor by simply probing the connector in the engine bay? Seems like it should output a voltage since it is a chemical reaction and not a powered sensor.

When do those usually fail? This one has 63k miles on it and is probably the original judging by the records I have.

thanks,
antony

Houpty GT

I do not know if your car has a heated sensor or not but the heated sensors typically last longer. The unheated sensor will cost you $17 to replace at Autozone. Do not buy the special Porsche sensor because it is exactly the same and you are just paying an extra $80 for a plastic connector that you alread have. You can hook a voltmeter to the sensor while it is still connected and the voltage should fluctuate back and forth from about 0.3 to 0.7 volts or so. If the voltage is not changing or takes a several seconds to change then you should probably change the sensor.

I am trying to find some more scientific information on 02 sensors, something only an engineer would be interested in, so if anyone knows of a source for this info I would appreciate the info.

Antony.

Thanks. I believe these are heated sensors. I'll take a voltage reading on it tomorrow. If it's working I'll have to see how much a smog shop will charge to give me a CO% reading to see if that was the issue.

DRACO A5OG

How old is the O2S?

Antony.

I think it's the original as far as I can tell. 1986 63k miles.

old man neri

It is a heated sensor and bentley recommends you swap it out every 60K. at 63K and 20 years old it might not be a bad idea. If it didn't fail it is bound to fail soon....or eventually

DRACO A5OG

+1

May want to replace if it does not pass DVM check.

Take caution when disconnecting it from the harness, the harness becomes very brittle. If you need to fix it I have a cheap fix but effect.

Jim

Antony.

DVM shows a constant 800 - 850mV at pin 1 with the engine warm and idling. When I unplug the sensor the idle speed increases notably.

DRACO A5OG

Is the reading only fluctuating between 800-850 mVs? if so, O2 Needs to be changed.

Base Idle may be too high. If you have the OEM 2K DME it should be at 800, if 4K DME 880 RPMs

Antony.

Yeah no real fluctuation. One set of measurements sat at around 850mV the next attempt was a constant 800mV. I'll get one ordered. Do people buy that special tool from pelican or use something else?

Any risk to any other components if I drive it in this condition?

DRACO A5OG

I used my cheapo chinese made adjustable cresent wrench. Just jack her up and use a jack stand for safety remove the left rear tire and replace with new one. It is pretty easy access.

Just remember not to plug in the O2S to sensor harness until the end of installation or it will twist up the wires and may cause binding. I recommend some Copper Anti-Sieze only on the thread.

Antony.

Cool, that'll save a bit of cash. Thanks for the help.

old man neri

If you have a 7/8" open end wrench that will work as well. It is going to require a bit of muscle to get the old one off no doubt, be prepared. Some soak with PB blaster or other overnight to help, not to sure if it actually does anything.

Antony.

Thanks, I'll pick up some PB Blaster, I've seen that mentioned in some other threads while researching this topic.

Is it better to have a constant 800mV signal coming into the ECM or 0V(floating)? Just wondering if I should disconnect it while I wait for the replacement to arrive.

DRACO A5OG

You can wait til she is cold to remove it, when it is hot the metal expands making it harder to remove. Just watch your knuckles, ask me how I know :-)

The reading shold be floating 0.5 volts with idle ( I guess 500 mV, I think?)