AEM AFR gauge going off the chart lean after throttle closure, Boosted application!!!

[jacob3318]

Ok guys Ive never seen this and Ive had my AEM logger in several vehicles but this is my first procharged one. 2019 sierra 5.3. I feel like this is a gauge problem not a tune issue! so the wideband works flawless under any throttle, but if you blip the throttle or come off of any kind of decent pull the gauge will go past 27 AFR and just display ---- Scanner logs it as 17.99. It stays there until the truck come back down to idle or I get back in the throttle.

I did remove the cats but heres the kicker, I own a custom exhaust shop, everything is welded perfect . absolutely no leaks, I even smoke tested the exhaust and not a pinhole anywhere!!!

Am I missing something? I want to say its never done this. any thoughts.

[jacob3318]

I would like to add the sensor is after the y pipe where both banks of the exhaust merge into the single pipe that goes to the muffler! I will be swapping it with a rear o2 sensor location tomorrow so its only reading on one bank and see if that helps any. I almost want to say it didnt start this until the cat cam out

[5FDP]

You've had to have heard of de-acceleration fuel cut off before right?

Watch the other data in the scanner. Watch your o2 sensors and watch your fuel injector pulse width. Both of those should drop out when your start coasting. This is why you see the lean reading on the wideband gauge.

[jacob3318]

I’m sorry for my ignorance. This is my first genV and it’s just not like any gen3 I’ve done. Sounds like it’s normal is what I’m reading correct sir?

[5FDP]

DFCO was still around in GEN 3 and GEN 4 computers. It's just more aggressive in my eyes on the newer vehicles because of emissions and trying to save all the fuel they can. In the GEN 3 vehicles you could always get DFCO to enable if you held the transmission in 3rd gear, floored it and started coasting. It never seemed to happen as much in drive.


So yeah, to me what you are seeing is normal. When you get another chance to log it, watch the injector pulse width and o2 mv readings, they likely do the same thing that you see on the wideband gauge.

[jacob3318]

Awesome. Thank you so much. I’ve never noticed it this bad on my gen3. I just thought I had something bad with the gauge itself seeing it register so high so fast.