I just took a look at the ALDL data from my 91 3.1L V6 today with the newest version of TunerProRT. My car started stumbling at idle a while ago n' i wanted to check out what the problem was... it turned out to be the coil wire, but while looking at the flags, i noticed that the computer was showing constant switching between open and closed loop. The motor was warm, and the O2 sensor flag was switching between ready and not ready, with a corresponding change between open and closed loop operation. Is this normal for a 730 V6? or is this an indication of a bad O2 sensor? no trouble codes as of yet however, and when it's in closed loop, everything functions normally with steady rich/lean crosscounts.
My 92 Z28 with the 730 doesn't exhibit this behavior so i just wanna know if this is a problem.

 

That's usually a sign of an O2 sensor not staying warm enough. Do you by chance have headers on the car? If not, does this only occur at idle, or all the time. If all the time, definitely try a new sensor.

 

I just hooked up the laptop again tonight and noticed that the ecm only goes into open loop when it's at idle. If i rev the engine, it shortly goes back to closed loop, only to return to open upon idle. I also discovered that the broken coil wire is not the cause of the stumble at idle and hesitation upon accel. The motor is simply running too lean. I was looking at the O2 voltage when the ecm was at open loop, and the reading are less than 400 mV, bout 300-340. Integrator stays at 124ish, and the BLM's are maxed at 114. When it's in open loop, there is obviously no compensation and thus the O2 readings are too low. I guess I'll see what a new O2 will do since they're relatively cheap. Oh yeah, at closed throttle, my TPS was showin .64 volts too... got that fixed.

 

Yes, with the O2 down under in the Y pipe it will cool off at idle. The '92 Z has the O2 up in the exhaust manifold, doesn't it?

RBob.

 

hhmmm... the 92 Z has the O2 in the header collector but it still gets hot enough. The sensor in the RS is not in the y-pipe as i recall, it's actually about the same distance as the 92.

 

Bet if you switch to a 3 wire heated O2 sensor your problem will "disappear".....

 

My mate has a similar problem I saw with his camaro switching from open loop to closed loop at idle. Looks like the exact same problem you have and he did not have headers at the time.

He has headers now so it was not because of the headers he had the problem. The exhaust guy who made his headers told him he has a hair line crack in the O2 sensor so maybe that is the problem.

So your O2 sensor might be stuffed and need replacing.