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('07 Cobalt LS, 2.2L Ecotec)

Using an OBDlink SX USB adapter and their OBDwiz app on an old laptop, I get the chart below. Engine is at steady (800 rpm?) idle, closed-loop. The displayed data has inflection points about 1/2 second apart. Does this imply that the ECU updates its setting every 1/2 second? Or, is the ECU actually faster, and the apparent timing is just due to limitations in the app/USB capability?

Bonus question: is that amount of variation in (pre-cat) O2 (2nd from top) and intake MAP (bottom trace) reasonable?

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I don't know for sure, but believe the ECU is faster than what you're seeing in your log. I'd suggest you check the settings to see if you can get a faster data rate showing from the program/app.

As far as the O2, the O2 sensor looks lazy. It should be hitting back and forth a lot more than what I'm seeing in the log. This could be a factor of the logging (of 1/2 second), though wouldn't know for sure. I'm used to seeing it jump back and forth quite radically for sensor 1 (pre-cat), then quite calm for sensor 2 (downstream). An O2 should last about 100k miles. If you've not changed it out and it's over this amount of miles, I suggest you look into it.

The MAP is going to show variations. Since it is at idle, I'm assuming the Idle Air Control (AIC) valve is doing its thing which causes the MAP to fluctuate a bit. All you are seeing there is about .6 in/Hg (8.3-8.9) difference from lowest to highest, which isn't very much of a swing.

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  • What are you using to monitor the signals? FYI, the O2 sensor isn't the concern; I have an intermittent p1174, "cylinder imbalance" code, and I was wondering if anything could be gleaned from watching the O2 or whatever signal. At 1/2 second, that's a big no. But, I got wondering whether that was really the ECU rate. Hence, the question.
    – George
    Jan 4 at 2:49

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