Is there a correlation between AFR reading and rich smell at idle
08-22-2011, 08:21 PM
#1
Is there a correlation between AFR reading and rich smell at idle I have a small cam in my car EPS 226/230 on a 112+2. TEA 5.3 heads, ported FAST 92
The car hunts idles when you cold start it, AFR is 12-13. About after two minutes the idle calms down and the AFR leans out to 14-15.
The car has been tuned by a reputable tuner. It needs to be taken back for some fine tuning but I think I might get HP tuners or the like and learn how to do it myself.
It smells rich at idle. I know it has a cam and no cats so I expect some smell. I bought the master efi tuning book and I am wanting to learn how to tune my own car. I keep hearing about 14.7:1 but I don't know what that actually is. I mean I know what it is but what THAT number is. I have read countless times on here @WOT the AFR should be 13:1.
What should it be at idle? Is it relative to cam size/engine size?
Thanks for any advice guys.
Jason
The car hunts idles when you cold start it, AFR is 12-13. About after two minutes the idle calms down and the AFR leans out to 14-15.
The car has been tuned by a reputable tuner. It needs to be taken back for some fine tuning but I think I might get HP tuners or the like and learn how to do it myself.
It smells rich at idle. I know it has a cam and no cats so I expect some smell. I bought the master efi tuning book and I am wanting to learn how to tune my own car. I keep hearing about 14.7:1 but I don't know what that actually is. I mean I know what it is but what THAT number is. I have read countless times on here @WOT the AFR should be 13:1.
What should it be at idle? Is it relative to cam size/engine size?
Thanks for any advice guys.
Jason
08-22-2011, 10:18 PM
#2
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There's 2 issues that contribute to a rich smell at idle. You're right - without cats, you'll always have some. But, the wrong injector timing and over-fueling idle are the main 2 reasons you'll have a problem.
I haven't done the math, but I'm sure your cam has at least some overlap in it. What that means is, there's going to be some unburnt oxygen that makes its way through the vavles and into the exhaust at idle. Oxygen sensors (wideband or narrowband) will pick this up as a lean condition and if closed loop is still enabled, the PCM will dump more fuel in. Ideally, the only way around it that I know of is to run open loop.
Also, adjusting the injector timing (so that it's not spraying so early) can help to elminate some of the unburnt fuel passing through into the exhaust. The stock cam has negative overlap (or a period of time where the intake valve remains closed after the exhaust valve has cycled). The engineers set the injectors to fire on the back of the closed intake valve to promote better vaporization of the fuel. Now that your exhaust and intake valves are open longer and overlap, that fuel is passing right through that overlap. Delaying that spray a bit will help to clean that up...and net you a few HP down low.
So, when you ask about a WBO2 reading - there's not a definite answer. 14.7:1 is what makes sense for the engineers trying to hit emissions standards and a good point to shoot for when cruising around. But, it's no magical number by any means. At idle, my car sees 17.5:1 with my cam's 18* of overlap....and it runs just fine.
I wouldn't expect yours to be quite so high. But, I also wouldn't expect it to be richer than 15.0:1....that's just going to be too rich.
I haven't done the math, but I'm sure your cam has at least some overlap in it. What that means is, there's going to be some unburnt oxygen that makes its way through the vavles and into the exhaust at idle. Oxygen sensors (wideband or narrowband) will pick this up as a lean condition and if closed loop is still enabled, the PCM will dump more fuel in. Ideally, the only way around it that I know of is to run open loop.
Also, adjusting the injector timing (so that it's not spraying so early) can help to elminate some of the unburnt fuel passing through into the exhaust. The stock cam has negative overlap (or a period of time where the intake valve remains closed after the exhaust valve has cycled). The engineers set the injectors to fire on the back of the closed intake valve to promote better vaporization of the fuel. Now that your exhaust and intake valves are open longer and overlap, that fuel is passing right through that overlap. Delaying that spray a bit will help to clean that up...and net you a few HP down low.
So, when you ask about a WBO2 reading - there's not a definite answer. 14.7:1 is what makes sense for the engineers trying to hit emissions standards and a good point to shoot for when cruising around. But, it's no magical number by any means. At idle, my car sees 17.5:1 with my cam's 18* of overlap....and it runs just fine.
I wouldn't expect yours to be quite so high. But, I also wouldn't expect it to be richer than 15.0:1....that's just going to be too rich. 
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08-23-2011, 12:19 PM
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What you interpret as "smelling rich" is probably high
HC, which can result from either over-rich or over-lean
mixture. Minor rich is mostly odorless CO. If it stings,
it's lean (Nox) and if it's sweet with no sting then rich.
Wideband reading is untrustworthy on a big cam motor
at low RPM. You may find the minimum-MAP fueling a
better thing to chase, this is the motor's "happy place"
and when you find it then you can tweak the O2 switch
voltages to whatever that average reading turns out
to be if you want to pull it there closed loop.
HC, which can result from either over-rich or over-lean
mixture. Minor rich is mostly odorless CO. If it stings,
it's lean (Nox) and if it's sweet with no sting then rich.
Wideband reading is untrustworthy on a big cam motor
at low RPM. You may find the minimum-MAP fueling a
better thing to chase, this is the motor's "happy place"
and when you find it then you can tweak the O2 switch
voltages to whatever that average reading turns out
to be if you want to pull it there closed loop.
08-23-2011, 12:31 PM
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What you interpret as "smelling rich" is probably high
HC, which can result from either over-rich or over-lean
mixture. Minor rich is mostly odorless CO. If it stings,
it's lean (Nox) and if it's sweet with no sting then rich.
Wideband reading is untrustworthy on a big cam motor
at low RPM. You may find the minimum-MAP fueling a
better thing to chase, this is the motor's "happy place"
and when you find it then you can tweak the O2 switch
voltages to whatever that average reading turns out
to be if you want to pull it there closed loop.
HC, which can result from either over-rich or over-lean
mixture. Minor rich is mostly odorless CO. If it stings,
it's lean (Nox) and if it's sweet with no sting then rich.
Wideband reading is untrustworthy on a big cam motor
at low RPM. You may find the minimum-MAP fueling a
better thing to chase, this is the motor's "happy place"
and when you find it then you can tweak the O2 switch
voltages to whatever that average reading turns out
to be if you want to pull it there closed loop.
I was headed down the too lean side of it.
08-23-2011, 11:25 PM
#10
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FYI if your looking for power on pump gas id go closer to 12:1, some tuners that like to err on the safe side go to like 11.2 but I think thats way to rich unless youve got water/meth then it tends to be perfect 
08-23-2011, 11:51 PM
#12
I took a short vid of the AFR gauge at idle tonight. I give it a little rev near the end.
http://www.youtube.com/watch?v=eQmejbbFs1w
Does it look like its switching correctly? This is with the car completely warmed up.
http://www.youtube.com/watch?v=eQmejbbFs1w
Does it look like its switching correctly? This is with the car completely warmed up.
08-24-2011, 02:21 PM
#13
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The digits look not-crazy, but this has nothing to do
with the narrowbands' switching behavior. And I am not
clear on whether the complaint is about cold open loop
or warm closed loop idle stank.
I do know that going back from long tubes to the JBAs
has hugely increased the reswitch rate on my NBO2s.
Which was one primary (heh) reason for doing it, I got
tired of having my trims pushed around by simple
thermal history.
with the narrowbands' switching behavior. And I am not
clear on whether the complaint is about cold open loop
or warm closed loop idle stank.
I do know that going back from long tubes to the JBAs
has hugely increased the reswitch rate on my NBO2s.
Which was one primary (heh) reason for doing it, I got
tired of having my trims pushed around by simple
thermal history.
08-24-2011, 02:58 PM
#14
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The digits look not-crazy, but this has nothing to do
with the narrowbands' switching behavior. And I am not
clear on whether the complaint is about cold open loop
or warm closed loop idle stank.
I do know that going back from long tubes to the JBAs
has hugely increased the reswitch rate on my NBO2s.
Which was one primary (heh) reason for doing it, I got
tired of having my trims pushed around by simple
thermal history.
with the narrowbands' switching behavior. And I am not
clear on whether the complaint is about cold open loop
or warm closed loop idle stank.
I do know that going back from long tubes to the JBAs
has hugely increased the reswitch rate on my NBO2s.
Which was one primary (heh) reason for doing it, I got
tired of having my trims pushed around by simple
thermal history.
08-25-2011, 01:37 AM
#15
I'm broke right now and just trying to learn some stuff.
I've never heard before that a lean condition can cause a eye watering effect.
08-25-2011, 06:46 AM
#16
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Like Jimmy said, an overly lean condition can cause a rich smell because the mixture is not dense enough to completely burn through and you will be pumping the unburned raw fuel through resulting in high hydrocarbons. A good EGA could show you this.
08-25-2011, 10:23 AM
#17
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The NOx (which is produced by lean conditions at
high cylinder pressure) turns to various nitric acids
when it hits water. Like your mucous membranes.
HC happens at either extreme of mixture, NOx only
lean, CO only rich. For shade tree figuring, the nose
is maybe the best tool you've got. Just don't wear
it out.
high cylinder pressure) turns to various nitric acids
when it hits water. Like your mucous membranes.
HC happens at either extreme of mixture, NOx only
lean, CO only rich. For shade tree figuring, the nose
is maybe the best tool you've got. Just don't wear
it out.
08-25-2011, 11:16 AM
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My CO picture is bad. I will need to rescan it.
If you have E10 and the PCM is set for E0 then these chart are off, but you can get an idea of how far it works. Also E10 burns differently then E0 and the exhaust makeup is different.
If you have E10 and the PCM is set for E0 then these chart are off, but you can get an idea of how far it works. Also E10 burns differently then E0 and the exhaust makeup is different.
