02 Sensor wire madness

[WB3]

Hello all,

The 02 sensor wire is really acting weird. The 02 sensor has been disconnected (inside the engine compartment) since the day I bought the car. I think it was when I was changing my fuel filter that I bumped the rubber boot that the wire goes into (or went into) that I noticed some white chunks fall from the boot. Needless to say, I had to take off the boot and see what was up. I guess engine heat and age made the plastic brittle and it just started to fall apart. I hooked up the sensor and got idle hunt and an overall poorly running engine. Signs of a bad 02 sensor. And I assume that's is why it was disconnected in the first place. I guess the PO didn't want to shell out the money for a new sensor and the engine ran fine (if not better) with it disconnected.

Anyway, I ran with the sensor disconnected and just the metal pigtail sticking out of what's left of the plastic thing the wire goes into. The idle rpm went up to 1200 or 1400. Now get this, I moved the pigtail and wire (which I guess goes to the Lambda brain) around a bit and the idle would drop back down to the normal 950. Let go of the wire...and it shoots back up to 1200 or 1400 rpm. The wire wasn't touching any metal or anything. This is to weird! Does the pigtail have to be sheilded or something? Can you just disconnect this wire directly at the Lambda brain? This one has got me scratching my head for sure. Any ideas?

[pjv911]

I know it uses a shielded wire . Could be voltage induction. Full output on a fresh o2 sensor is 1 volt. If the signal wire got a value of 100 mv from static voltage coming from..... lets say a poorly grounded alternator , then your control module will respond to a lean condition (100mv) with a duty cycle change to the frequency valve . The results would be exactely as you described and its not strange at all. Thats why the original pigtail connecter is so insulated. Notice the wire below the tin is unshielded and with barely any insulation . Chances of having static voltage below the tin is unlikely . Get a new 02 sensor and a new pigtail. Otherwise just tuck the signal wire away up by the shock tower(after wrapping it with e-tape of course)

Kurt Williams

[WB3]

Thanks Kurt,

Hmmm, that makes sense. I guess when I put the pigtail in my fingers and move it around, in effect, I'm sheilding the wire. Now where the plastic is broke off, I can see hints of copper wire on the outside of the main insulated wire with the pigtail. What this is I don't know. Do you think I could be getting some static electricity off the plug wires? I guess it can come from anywhere really. Anyway, I've got to change my fan belt tomorrow and I'll tackle the wire then. Thanks for the reply!

[ischmitz]

It sure sounds like noise radiating into the wire. Either disconnect the wire closer to the brain or ground it.