How closely should AFRs be monitored when not WOT?
 

I have the kraftwerks supercharger and have been noticing some odd AFR behavior. Or at least odd to me, could be completely normal.

So when accelerating from a light, using pretty much the bare minimum of throttle to let the rpms climb, in third gear around 3,200-4,200 I've noticed my AFR dip into the 15's. It's happened quite a few times and I'm curious as to if that's just being paranoid and it's nothing to worry about since I'm obviously not harping on the car. It's usually only under load too, if I'm trying to "push" the car and gain momentum, like if you're just maintaining speed and want to go faster they rise to the 15's then go back down.

At WOT it never touches that range, and is in the 11's where it should be. Am I just babying the gas pedal too much? Tuning issue? I'll try to get logs if needed.

At light part throttle, it should be aiming for stoich which is ~14.7, if it's in the low 15's I wouldn't worry at all.

Are you monitoring it with a proper wideband and matching gauge, or logging it through the stock O2 sensor?

That'd be closed loop, the AFR will fluctuate as the ECU tries to keep up. So long as it's not going really lean then I wouldn't worry.

The AFR's I'm describing are only what I've seen through my AEM failsafe that is in the rear O2 port of my header.

Is it in plugged into your ecu?
If so, get visconti if he is still your tuner to run it full close loop?

It is plugged into the ecu, the only problem is that I don't have it connected to an analog ground. Not sure what I can use for analog ground. Otherwise the AFR readings in ecutek are always off by +1.

Doesn't matter if it's connected to your ECU or not, if it's just going slightly into the 15's and not doing it all the time I wouldn't worry at all.

Something must be wrong. I took it out at lunch today and while accelerating it stayed in the 14's, then shot up to 15.9 and stayed there for about 2 seconds and didn't seem to budge. I then shifted into the next gear and it went back down to 14's then I put my foot into it and it went back up this time to 16.

All around 3,800-4,500 rpm, half throttle. I wish I could have got it on video. I'm going to to log it in ecutek and pull the battery after work and see if it still does it. I've never seen this high of AFR before.

If you're logging, check fuel system status to see if you're in CL while its doing this. Its not unusual for the AFRs to wander and in CL there's not much you can do. Also if you come off the throttle it will show leaner. Its not an issue going lean unless you start putting load on the engine.

Could be your MAF scaling is off? Happens to mine when leaving closed loop to open loop. It will lean to high 15 to 16 AFR because my stock MAF scale is making my requested AFR about 1 AFR richer then my true AFR. Could be the same problem? I haven't gotten around to fixing mine yet but maybe this weekend.

I've attached two logs. I can see where the engine load is coming up and it's hitting close to 16 afr. I don't really know how to read these logs too well, can you guys help me?

The KW kit has a lot of turbulence in the MAF due to its placement in front of hte throttle door. So if you tune the MAF perfect at WOT and then drive at partial throttle the maf calibration is off. The fuel trims will compensate for this and they are doing so in your logs. It is swinging a fair bit but its not that is extremely bad. You aren't sustaining high AFR's for long periods of time and are typically under very low load at the time. However we would need to see more info to dig more into it. I noticed that when you go into open loop at times you are running a fair bit lean even with some load on the engine go to 143,443MS in your log and you'll see your sitting around stoich. However this could be the actual requested value in your tune for all I know.

We would need to see more detail in the logs. Try relogging with MAF V, SD volumetric efficiency and Equivalence ratio commanded AFR.

It would more-so be a problem if your fuel trims were completely maxing out and you were leaning out. Your fuel trims are not breaking into the +30's in an attempt to richen the mixture.

Also its usually its best to talk to give your tuner a call if you are concerned with something like this.

Please clarify: you are looking at an AEM/Bosch wideband located in the rear O2 sensor bung. Are there any catalysts in front of it?

Catless borla header.