Unstable AFR at low throttle
Jun 27, 2008, 05:54 AM
#1
Unstable AFR at low throttle
Hello everyone,
I've been having some troubles with AFR jumping around since we installed new plugs, downpipe and testpipe. We've checked for leaks, swapped out the plugs back to the old ones and new ones - not related.
It seems to be happening only in closed loop or well, under 25% throttle atleast when cruising or at standing still. I recorded a movie with my phone that has a really awesome camera (sarcasm off) but I think if you look real close you can see the AFR light on the wideband jumping up and down. I'm holding throttle at 2000 RPM steadily and it's jumping like this.
http://www.youtube.com/watch?v=ubfShI_RpL4
Also I attached a quick log of the same thing being done (not the movie one tho) - standing still holding it at 3k rpm. The AFRs are this jumpy at cruising aswell. No knock or whatever, just AFR jumps from 14-15.5
Now as I wrote it seems to be happening at low load. WOT runs give perfect readouts and the wideband seems to be showing correct values. What could be causing this? I'm pretty much stomped.
Edit: Mods are 3" downpipe & testpipe. K&N cone filter (been there for a long time, didn't give any problems before the downpipe and testpipe install), Walbro and AVC-R
I've been having some troubles with AFR jumping around since we installed new plugs, downpipe and testpipe. We've checked for leaks, swapped out the plugs back to the old ones and new ones - not related.
It seems to be happening only in closed loop or well, under 25% throttle atleast when cruising or at standing still. I recorded a movie with my phone that has a really awesome camera (sarcasm off) but I think if you look real close you can see the AFR light on the wideband jumping up and down. I'm holding throttle at 2000 RPM steadily and it's jumping like this.
http://www.youtube.com/watch?v=ubfShI_RpL4
Also I attached a quick log of the same thing being done (not the movie one tho) - standing still holding it at 3k rpm. The AFRs are this jumpy at cruising aswell. No knock or whatever, just AFR jumps from 14-15.5
Now as I wrote it seems to be happening at low load. WOT runs give perfect readouts and the wideband seems to be showing correct values. What could be causing this? I'm pretty much stomped.
Edit: Mods are 3" downpipe & testpipe. K&N cone filter (been there for a long time, didn't give any problems before the downpipe and testpipe install), Walbro and AVC-R
Last edited by Toxin; Jun 27, 2008 at 05:57 AM.
Jun 27, 2008, 07:55 AM
#3
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How many miles on that wideband O2 sensor? Where is the sensor located?
Honestly, I don't think its a big deal. 14.7 is what its supose to read at those loads and they could still bounce around a bit.
The problem could also be your front O2 sensor in the O2 housing too.
Honestly, I don't think its a big deal. 14.7 is what its supose to read at those loads and they could still bounce around a bit.
The problem could also be your front O2 sensor in the O2 housing too.
Jun 27, 2008, 08:15 AM
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14 -15.5 is a more than normal at idle or cruise. Mine is usually 14.7-15.2 at cruise and a little leaner at idle. It bounced normally but not from 14 - 15.5.
Jun 27, 2008, 08:19 AM
#6
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My experience is when an o2 will get stuck permanently. ex: 14.7/14.8 or wherever it was last. Right before it dies it may go real rich or real lean as well.
Jun 27, 2008, 08:19 AM
#7
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yea, i just watched the video and im pretty sure my car is exactly the same while cruising. i dont think its at all possible to be 14.7 dead on without fluctuating. my car idles at 900 rpm and afr goes 14.7-15.2. occasionally it will sit at 14.7, to 14.8, back to 14.7 really steady.
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Jun 27, 2008, 08:29 AM
#8
I opened this topic because before the mods - it was actually normal. If I was cruising on a straightaway at let's say 60mph I would have a consistant 14.7 +/-0.2, now it's CONSTANTLY bouncing up and down really fast, up and down and up and down. I guess it's nothing to worry about but it's annoying the hell out of me 
Jun 27, 2008, 08:39 AM
#9
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im with you on that. ive faught with my car over not being able to have a steady afr at idle. like i said in my reply. occasionally i have a steady 14.7 at idle. but the times that it isnt steady, its sweeping 14.7-15.2 and then whenver it feels like it, 12.5-13.0 back to 14.7 then back to 13.0. it something that annoys me, but it comes with modding the car. i realized that when you mod your car as much as i have, eventually you have to give up the stock driveability. as far as i see it, afr is gonna be all over the place, but steady at wot. and wot is what im concerned about when it comes to afr.
Jun 27, 2008, 06:40 PM
#12
im with you on that. ive faught with my car over not being able to have a steady afr at idle. like i said in my reply. occasionally i have a steady 14.7 at idle. but the times that it isnt steady, its sweeping 14.7-15.2 and then whenver it feels like it, 12.5-13.0 back to 14.7 then back to 13.0. it something that annoys me, but it comes with modding the car. i realized that when you mod your car as much as i have, eventually you have to give up the stock driveability. as far as i see it, afr is gonna be all over the place, but steady at wot. and wot is what im concerned about when it comes to afr.
WOT is being taken care of by Tamer (4Wheel Slide) and that's working... More than properly !
Jun 28, 2008, 12:29 AM
#14
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If you change the volume of the exhaust between combustion and where the O2 sensor is located, you also effect O2 feedback. Going larger in volume will increase the "swing" of AFR due to the delay in the change of AFR being detected by the O2 sensor. This should only have an effect if you moved the O2 sensor further away, but if it is in the same general location it wont be the cause of the problem. Something to think about anyway.
Jun 28, 2008, 06:20 AM
#15
If you change the volume of the exhaust between combustion and where the O2 sensor is located, you also effect O2 feedback. Going larger in volume will increase the "swing" of AFR due to the delay in the change of AFR being detected by the O2 sensor. This should only have an effect if you moved the O2 sensor further away, but if it is in the same general location it wont be the cause of the problem. Something to think about anyway.