AFR values being weird
#1
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Join Date: May 2008
Location: Nashville/Knoxville, TN
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AFR values being weird
So I got this weird issue with AFR's, or maybe my wideband gauge lately. I'll make a video of the gauge soon, which makes it very clear, but basically when its idling the AFR's will jump around a good bit, like 14-14-14-15.7-15-13-13-13.5-14-14 It does it all the time, several times a minute, once the car is up to temp. It always jumps to lean, then slightly below where I want it, then back where I want it, then immediately does it again. It does it a tiny bit cruising, but its much more exaggerated while idling. I thought it could be ignition missing, but I don't know why that would get it to jump lean. the car drives fine, no jerking or anything when it happens.
Any ideas? AEM UEGO btw.
Any ideas? AEM UEGO btw.
#15
Boost Czar
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Work on your tune. It's more than likely your fuel map doesn't have enough resolution where you are idling and it's jumping around a few cells that have large changes in the VE%.
Rescale your entire fuel map to scale from 20-100kPa not 20-255kPa and run the high-res code.
Rescale your entire fuel map to scale from 20-100kPa not 20-255kPa and run the high-res code.
#16
Then again, a lot of stock ECUs do this too.
#17
Boost Pope
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Idle AFR is typically more stable if you are in open-loop while at idle. When you're in closed-loop, the gEGO mechanism makes relatively large changes to the mixture, causing this swing.
It's not hurting anything.
Variations in idle AFR are often the result of bumps and dips in idle speed (such as an isolated misfire) or fluctuations in the position of the idle control valve, rather than the cause of same. IOW, when the IAC valve changes position, MAP and RPM both change in response. Correction and stabilization of fuel mixture tends to lag this change slightly, resulting in a momentary fluctuation in AFR. This same effect is observable during steady cruise- if you suddenly press down on the pedal, the AFR will momentarily spike lean, whereas if you suddenly let up on the pedal, the AFR will momentarily spike rich. Damping the action of the IAC valve reduces the severity of this phenomenon, although slowing it too far will exacerbate it by allowing idle to drift too far, thus resulting in rapid recovery attempts.