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Old 01-02-2009, 02:55 PM   #1
N3v
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Default 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.
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Old 01-03-2009, 02:11 AM   #2
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Tried cleaning the ground? Any way to do a recalibration on that? Could it be megasquirt related? If so datalogs posted up might help.

just a few quick thoughts.
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Old 01-03-2009, 10:48 AM   #3
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That actually sounds pretty normal to me.
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Old 01-03-2009, 11:13 AM   #4
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Mine does that too. And if I make a wide open run, when I let out, it goes blank for a second.
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Old 01-03-2009, 12:03 PM   #5
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Thats why I don't have a gauge, I just do weekly 3rd gear logs.
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Old 01-03-2009, 02:07 PM   #6
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huh. i don't think it used to do it before. oh well.
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Old 01-03-2009, 03:26 PM   #7
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I can't comment on if it is normal or not, but I just put my lc-1 in two days ago and it jumps around at idle almost exactly like you have described...
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Old 01-03-2009, 03:54 PM   #8
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idle afr is not stable as joe said
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Old 01-03-2009, 05:46 PM   #9
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Normal.
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Old 01-03-2009, 07:07 PM   #10
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could also be that ITB's idle at 1krpms and at 50kpa :P
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Old 01-04-2009, 01:02 PM   #11
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Anything is possible.

But really, worry about sudden lean events when driving. At idle, it wont make much of a difference.
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Old 01-04-2009, 01:35 PM   #12
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Sounds normal, at idle mine jumps around from 14.5 to 15.2 ish
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Old 01-05-2009, 03:40 PM   #13
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Why does this only happen to MS? My other friends with Hydra and Links are almost perfect. Mine will jump around 14 15 16..
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Old 01-06-2009, 03:19 AM   #14
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Mine is still on the stock ECU
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Old 01-06-2009, 09:57 AM   #15
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Quote:
Originally Posted by N3v View Post
could also be that ITB's idle at 1krpms and at 50kpa :P
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.
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Old 01-06-2009, 12:33 PM   #16
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Quote:
Originally Posted by Sleeper_MX5 View Post
Why does this only happen to MS? My other friends with Hydra and Links are almost perfect. Mine will jump around 14 15 16..
Could be a matter of too much EGO correction. Another possibility if you're running large injectors is that you are close to the limit of the MS1's resolution, which is about 0.1 ms. So with large injectors, a jump from a 1.5 ms pulse width to 1.6 ms is a pretty significant difference in fueling.

Then again, a lot of stock ECUs do this too.
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Old 01-06-2009, 01:00 PM   #17
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Quote:
Originally Posted by Sleeper_MX5 View Post
Why does this only happen to MS? My other friends with Hydra and Links are almost perfect. Mine will jump around 14 15 16..
A couple of observations.

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.
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Old 01-06-2009, 01:07 PM   #18
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Originally Posted by N3v View Post
could also be that ITB's idle at 1krpms and at 50kpa :P

My webcam 505's idle at 1krpms 50kpa. AFR fluctuates as has been described. Fuel numbers at idle range from 29 -32 to compensate.
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Old 01-07-2009, 04:05 PM   #19
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Quote:
Originally Posted by Saml01 View Post
Anything is possible.

But really, worry about sudden lean events when driving.
I worry about these, I am having a very hard time tuning them out.
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Old 01-07-2009, 04:26 PM   #20
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Quote:
Originally Posted by skidude108 View Post
I worry about these, I am having a very hard time tuning them out.
Listen to Braineack. He makes an excellent suggestion. Rescale your VE table and run hi res code.
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