question as to AutoMeter AFM readings?
03-24-2003 | 09:00 PM
#1
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Three Wheelin'
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From: Winterville, NC
question as to AutoMeter AFM readings?
My Idle is a bit roughter than I would like and ocassionally drops a few RPM. I was noticing that my AutoMeter AFM 'dithers' from full lean to the last yellow or 1st green very rapidly and smoothly while cruising. But at idle, it dithers much slower, same range, just much slower, and when it drops a few RPM, the gauge will 'hang' on full lean for a split second, then return rich and the RPM will recover.
How does this compare to you guys, perferibly someone with a rock steady idle.
How does this compare to you guys, perferibly someone with a rock steady idle.
03-25-2003 | 06:07 AM
#2
Race Director
The dithering speed will always be slower at idle than at cruising speed. Not sure exactly on the O2-feedback correction algorithm, but it's not done at a fixed time-slice, but rather based upon numbers of engine revolutions.
"and when it drops a few RPM, the gauge will 'hang' on full lean for a split second, then return rich and the RPM will recover."
Sounds like a vacuum leak or a bad idle-stabilizer. The stabilizer circuit will play a catch-up game with the O2-sensor feedback. With a more severe vacuum leak, you'll actually get a rhythmic idle speed that goes up and down by 200rpms or more.
"and when it drops a few RPM, the gauge will 'hang' on full lean for a split second, then return rich and the RPM will recover."
Sounds like a vacuum leak or a bad idle-stabilizer. The stabilizer circuit will play a catch-up game with the O2-sensor feedback. With a more severe vacuum leak, you'll actually get a rhythmic idle speed that goes up and down by 200rpms or more.
03-25-2003 | 01:24 PM
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Burning Brakes
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From: Baton Rouge/New Orleans, LA
I just got a modified Autometer A/F guage from <a href="http://gadgetseller.com/gauges/" target="_blank">http://gadgetseller.com/gauges/</a> This is a modified a/f guage that does not bounce around during normal driving but it works only on WOT, which is when you need to know what is going on. It is recalibrated and is much more accurate than a stock A/F guage.
03-25-2003 | 04:24 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by ringo951:
<strong>I just got a modified Autometer A/F guage from <a href="http://gadgetseller.com/gauges/" target="_blank">http://gadgetseller.com/gauges/</a> This is a modified a/f guage that does not bounce around during normal driving but it works only on WOT, which is when you need to know what is going on. It is recalibrated and is much more accurate than a stock A/F guage.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">According to the vendor Web site, the modified gauge merely expands the "rich" region of the stock gauge, making it possible to resolve smaller differences in that region. However, the gauge "accuracy" ultimately depends on the underlying accuracy of the O2 sensor in converting A/F ratio to a voltage. The O2 sensor is very nonlinear in the rich region and also temperature dependent. It seems that any indication in the rich range will still be a pretty crude measure of A/F, but certainly better than nothing.
Nonetheless I like the idea because the dithering of the stock A/F gauge at idle and cruising makes it pretty useless there anyway, so that information might as well be suppressed. Furthermore, at night I find the dithering lights display to be quite distracting (with the gauge mounted in the A-pillar). I think I will send my gauge to these folks and get it modified.
<strong>I just got a modified Autometer A/F guage from <a href="http://gadgetseller.com/gauges/" target="_blank">http://gadgetseller.com/gauges/</a> This is a modified a/f guage that does not bounce around during normal driving but it works only on WOT, which is when you need to know what is going on. It is recalibrated and is much more accurate than a stock A/F guage.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">According to the vendor Web site, the modified gauge merely expands the "rich" region of the stock gauge, making it possible to resolve smaller differences in that region. However, the gauge "accuracy" ultimately depends on the underlying accuracy of the O2 sensor in converting A/F ratio to a voltage. The O2 sensor is very nonlinear in the rich region and also temperature dependent. It seems that any indication in the rich range will still be a pretty crude measure of A/F, but certainly better than nothing.
Nonetheless I like the idea because the dithering of the stock A/F gauge at idle and cruising makes it pretty useless there anyway, so that information might as well be suppressed. Furthermore, at night I find the dithering lights display to be quite distracting (with the gauge mounted in the A-pillar). I think I will send my gauge to these folks and get it modified.