Originally Posted by gojo83
just curious if o2 is just a mpg thing not a engine variant because the o2s are good when on the gas but on cruise and off the gas they are crazy.
What you are seeing is perfectly normal. Your scan tool or the O2 sensor isn't screwed up.
What is happening is this:
1.) The O2 sensor is slow to react, it always lags behind. A heated O2 sensor comes online a little quicker, since it doesn't rely on the exhaust gas to heat it up to it'* operating temp. But both are slow to react to changes in oxygen content in the exhaust.
The ECM isn't screwed up by this, the software in it already knows when to ignore the O2 readings because the engine temps are not up to the operating range yet.
2.) At very low RPM (idle), you can see the individual pulses of hot gas going past the O2 sensor, so the "frames" of data being given to the scan tool are catching the gaps, so it apears the O2 values are all over the place. This doesn't screw up the ECM either..it sees the O2 values many more times than it'* reports to the scan tool via the serial data connector.
3.) At cruise, the ECM intentionally cycles the mixture rich-lean-rich-lean... This is done to oxygenate the catalytic converter'* brick..leaving enough free oxygen in the cat to react with the hot exhaust gas. This is why the 3800 motor doesn't employ an air injection pump...the ECM is adding oxygen to the cat on it'* own via the mixture. This also doesn't screw up the ECM...it'* software is intentionally doing this and knows what it should see on the O2 sensor during these cycles.
End result is you will drive yourself nuts trying to follow O2 readings. The only time you look at O2 values is during WOT acceleration..a state when the ECM goes into power enrichment mode and stops cycling the mixture. At less than WOT, look to the BLM and Integrator values to see how the ECM is reacting to the engines mixture. A 128 score on the integrator and BLM is perfect...the ECM is computing a perfect injector pulse without having to add any additional adjustment to the calculation.
To simplify this a little..Integrator is "short term" adjustment. What it means is that based on the last couple of readings of the O2 and other sensors, by the ECM, the ECM is going add or subtract the integrator from the computed pulse width.
BLM ("Block Learn Mode") is the long term adjustment...if the ECM keeps having to adjust the integrator over a few cycles in the same direction, then it will add to the BLM to shift the whole pulse width calculation in that direction.
Both are 1 byte variables in the ECM...minimum value is 0, maximum is 255, right up the middle is 128. The closer the integrator and BLM stay near 128, the better the match between the tables used to calculate the fuel injector pulsewidth are to the actual motor the ECM is controlling.