Two questions for those with experience, actually:

First, how does an O2 sensor behave when it's too cold (like the heater not working in headers, for example). Does it read lean, or just drop to zero? In other words, will I get false readings, or just no readings at all?

Second, does the ECM have to actively do something to read the O2? Or, should I see O2 readings in the ALDL data even when in open loop?

I'm confused because when I fire up the car, the O2 starts out around 450 mV (I've heard because the ECM is biasing it or something), then slowly drops to 0 mV and basically stays there until the system goes closed loop. This is even when the tune is close (the BLM's in closed loop are close to 128).

What could explain this behavior? I'd expect that if my VE tune is good, that my O2 readings would be close to 450 mV even though the system hasn't gone closed loop yet. I know the O2 has to heat up, but it's so coincidental that it starts giving good looking readings right away when it goes closed.

Any ideas would be great.

 

I have a single wire non heated O2 and headers and the O2 hovers around .45 volts untill it warms up enough to start working. IIRC, it acts as an open circuit untill above 600 some odd degrees. Even the 6 some odd minute delay to closed loop isnt enough sometimes if its really cold. The O2 wont move very far away from .45 volts when in closed loop and the engine runs kinda funky untill it warms up. From the description you gave of your problem, it sounds as though your just lean. A heated O2 would quickly warm up and register low voltage due to the lean mixture.

 

I guess I could still be lean. My idle is screwy, the O2 always reads lean even when everything else seems to be coming into line. All I can think of is exhaust leak - like maybe it leaks just a tad and then heats up and seals the leak... or something. I'll keep banging my head against it until I figure it out.

Thanks for the info.

 

I am having a similar issue w/ my car and the O2 showing lean, but mine is having issues never getting to closed loop. Maybe b/c the O2 is never seeing 600mv which as I understand it is a requirement to turn over into closed loop. I could be running lean at idle, but from the smellometer the car is extremely rich at idle. Start up the car and I see 250-350 for a while, and that is it... once warm it settles in the 250-300 range...

Sux cause it never goes closed, so i just dump fuel in...

Wish I could figure my issue out...

Good luck to ya though!!!