Wilson

With the key on the "ON" positon without the engine running, my O2 values are Left (0.514mV) and Right (0.451mV). I dont think this is normal. Do you think either the O2 sensor is bad or its Thunder Racing's O2 sensor wire extender or A/F ratio gauge thats tapped into the O2 wire that is causing the different in voltage?

Any ideals? BTW- theses are single wire O2 sensors on my 93.

97Z-M6

o2s dont matter until closed loop.

Wilson

True but your O2 values before starting the car should be the same. Mine are ~12% different in voltage. If this is the case it can lead to a split BLM value when in closed loop.

Anyone else check their O2 sensor values before running? What are your values and how are your BLM values?

Projectz28

you cant look at them when off. O2 sensors... especially 1 wire are not at all right when they are cold. They need to be at operating temp of ~750* or more before you can even begin to look at them.

Wilson

How would you be able to tell if one's bad? Right now at startup and in Open Loop the BLM are 124 & 128 and when they are heated up and in closed Loop it shows a slight split. Im wondering if this has something to do with the O2's starting voltage. Im assuming that there is more resistance in one O2 sensor then the other. Almost all the datalogs that I've seen and logged for others, I've noticed that the startup O2 values are dead on. This is why im beginning to question if I have a bad O2 sensor or a possible wire problem.

Projectz28

well the only way to truly test an O2 sensors is with some pretty high tech emissions monitoring equipment... they dont work on resistance. They actually produce a voltage output of their own with a chemical reaction between the lelment and excess o2 in teh exhaust. The heat is needed for this reaction to take place. The easiest thing to do is just put some new ones in.... when in doubt, throw it out!

Wilson

Yeah, its only $30 bucks. But money is not really the problem, its the pain in the **** location where the O2 sensor is located on my SLP ypipe. Driver's side isnt too bad but the Passenger side is almost impossible to get to without dropping the ypipe and header. Too much work to just "TRY".

Projectz28

It might not be physically the easiest, but you could trouble shoot it for a long time, spend lots of money and still not know for sure. For the $30 and a few hrs of your time its by far the "easiest" thing to do

As for the wiring, you can pull the ecm and o2 connectors and check resistance thru the harness by checking from the sensor connector to the ecm connection. I would think you should not see any resistance at all...

shoebox

Doesn't sound all that unusual to me. The sensors should get 4.5-5v.

[edit] Oops, I meant 450mv-500mv, not 4.5v .

Injuneer

The O2 sensors don't get 4.5-5V..... it appears that the PCM applies a .450V (450mV) bias signal, and when the sensor is cold, and not producing any voltage of its own, the 450mV reflects back to the PCM. On cold start, mine are (were - don't use them any more) always in the range of 450mV on both sides. I see his concern.... although I don't know if its a problem. Almost like there is some voltage leaking into the harness wiring at some point. And if the voltage of "incorrect" when the sensors aren't working, its conceivable that this same degree of difference would be preserved when the sensor heats up and starts producing its own +/- voltage.

Wilson

Could it cause my BLM's at start up to be off? I noticed in Open Loop they start off at 124/128. Maybe its related to the ECM reading a higher voltage on oneside and self adjusts the BLM value before it hits Open Loop?

Projectz28

If you have a split on cold start up then I belive the problem is in the fuel map programing in the PCM. The PCM does not use the o2 sensors for a/f ratio in open loop. It ignores them and goes off of a set of pre-programed tables. When coolant temp has reached a certain level, the PCM then looks at o2.... it assumes the o2's are hot by this point because the engine must have been running long enough to heat them up, since coolant temp is up. Since there are no exhaust temp sensors GM just used coolant temp as a referance to know when the o2's should be at operating temp.

now once into open loop if your BLM's are still split then there is some other reason causing the PCM to adjust it that way.

Injuneer

While the PCM ignores the O2 sensor on startup, it doesn't ignore the stored long term fuel corrections for Cells 16, 17 and 18. It locks the short terms, because it has no data from the O2 sensors to alter the short terms.

And there are no magical "tables" for open loop operation, it runs exactly the same as it does in closed loop, except it ignores the O2 sensors and it uses a target A/F ratio that is dependant on coolant temp.

It doesn't "assume" anything about the heatup of the O2 sensors... if it doesn't see the required activity, it knows they are not heated up and doesn't go into closed loop. It also looks at the coolant temp, and a timer, but it doesn't just assume the O2 sensors are working.