O2 cross counts

[Nathen]

What are O2 sensor cross counts and how do they affect how the ECU sees the AFR

[charlay86]

In closed loop fuelling, the PCM/ECM continually forces the mixture to change from slightly rich to slightly lean and vice versa.
Cross count refers to the number of times the O2 sensor voltage crosses the stoichiometric point in a fixed period of time.

[Nathen]

is there a "magic" number the ecu should see if it is fueling correctly, This would be steady state such as at 2000 rpm.
The engine I am looking at has a custom tune running in a Gm730 euc, Looking at the Blm you would think that the AFR was about right but it smells rich and pops and carries on through the exhaust. The O2 sensor is a three wire heated unit and has probably less that 10 engine hours on it, so I am trying to decide weather it is the problem or not.

[antus]

the ecu will only go in to closed loop if the fuelling is about right, so if you are seeing good BLMs and cross counts then the fuelling shouldnt be too far wrong. Does it pop and crackle only on decelleration? Its possible that the deceleration enleanment has been messed with so that it overfuels on decel just to make it sound like a race car or something.

[Nathen]

No does it a steady rpm, say 2000 If you go out and thrash the living shit (and I mean thrash it, High rpm WOT) out of it it will settle down for a while then it will start to run worse and worse.
Here is some of the data we logged

[34blazer]

what mask/bin are you using, $8D?

[darcy]

If that's in closed loop, which it looks to be is INTs are active, then that is not a great looking O2 trace, but at least it is swinging, and the trims aren't huge.
If it's an old sensor it might be worth a replacement.

[Holden202T]

yeah its definately not the swinging i'm used to seeing!

[Nathen]

Well today after doing all the usually things again(comp test, lifter settings ect ect) In desperation we replaced the brand new coil with a second hand one we had on the shelf,and guess what, no more backfiring. Ran out of time to gather data. Will be most interesting to see what the O2 sensor trend looks like, Hopefully if this issue is sorted we can get on with some tuning.