What would make an O2 sensor read Neg. Voltage?

awilson40 · 01-29-2003, 06:07 PM

I just replaced the O2 sensor (soldered in a universal replacement) It was reading normal ( +.2 to +.8vdc) then today the car was running very rough, unplugged the sensor, and it runs fine. The 'new' sensor is now putting out neg .8v at idle. I adj the AFM mix and brought it to zero, but when I accel, the voltage goes to neg .7 vdc.
No vac leaks can be found and the car runs great without the O2 sensor, pluggs look fine and no over rich signs.

awilson40 · 01-30-2003, 02:31 AM

I wish that were it

but no, the leads were correct

Scott R · Scott R's Garage

This does not sound like an O2 sensor issue.

How's your boost?

Any missfing going on?

Britwrench · 01-30-2003, 07:30 AM

What diagnosis have you done up to now? The 02 sensor only monitors the system; don't forget it checks Oxygen not Hydrocarbons.
I'd guess the fuel pressure is not right, or you have an air/vacuum leak.

awilson40 · 01-30-2003, 12:01 PM

I've replaced a leaky bypass valve, replaced a bad TPS,checked the AFM. Repaired any vac leaks I could find. As I said, the O2 sensor is reading negative voltage...This isnt suppose to happen. When I replaced the sensor, Its idle voltage was .8 v. I adjusted the AFM screw to open until the sensor was cycling between .3 and .7 v. Then, after 3 days, the sensor is reading negative .8v. Today...Its reading like it should, Positve voltage. Crazy stuff.

awilson40 · 01-31-2003, 02:36 AM

Cauzomb,
The O2 sensor is ignored when you are full throttle. My car runs great with the sensor disconnected with just a slight bit of miss. I would replace your fuel filter and check your fuel pressure regulator. Perhaps your pump is marginal. If you are going lean, then you are running out of fuel on top. What mods are you running? If you have disabled the factory boost protection and are running more boost without new chips to add more fuel then this will happen...If you are running chips you could be asking for more fuel than the stock injectors can handle. If you are running more than 15psi of boost, dial the boost back to 11 psi and see if you still run lean.
I think my problem is a clogged injector. AS far as my O2 generating neg. voltage... I think its because I soldered it and it cant draw reference air. I need to remove the solder and crimp the connection.