Idle smells rich but all sensors say lean.
10-03-2007, 06:13 AM
#1
TECH Resident
Thread Starter
Idle smells rich but all sensors say lean. I have a mild cam 226/226-112. I believe its only 2 degrees of valve over lap.
Driving around the AFR is pretty spot on and the O2 are in closed loop the WB is occilating around stoch, so I'm happy with that. Now i come to idle, my WB is showing 17:1 AFR. Pretty lean, not too bothered as its under no load. LTFT's around -12, O2's around 400mV (not occilating) So stock O2's think I'm rich, therefore taking away fuel.
So is WB seeing unburnt oxygen due to small amount of valve overlap?
I guess my O2's are off due to being in long tube headers, they seemed to work fine before heads and cam install.
All i know is, gauges are showing lean condition, yet I can smell its really rich.
I've got some Bosch 13111's on order so that may help me out.
Driving around the AFR is pretty spot on and the O2 are in closed loop the WB is occilating around stoch, so I'm happy with that. Now i come to idle, my WB is showing 17:1 AFR. Pretty lean, not too bothered as its under no load. LTFT's around -12, O2's around 400mV (not occilating) So stock O2's think I'm rich, therefore taking away fuel.
So is WB seeing unburnt oxygen due to small amount of valve overlap?
I guess my O2's are off due to being in long tube headers, they seemed to work fine before heads and cam install.
All i know is, gauges are showing lean condition, yet I can smell its really rich.
I've got some Bosch 13111's on order so that may help me out.
10-03-2007, 06:26 AM
#2
If using HP Tuners, check the status bits to see if your in closed loop at idle. Also you should be in fuel trim cell 19 at idle with AC off.
Did you tune the VE and MAF tables with your WB going into your tuning software? Bump your idle up 50 RPMs and see if that makes a difference.
It will smell at idle especially if you don't have CATs, even with a cam like that. I have a 226 222 116lsa cam and it still stinks a bit.
Did you tune the VE and MAF tables with your WB going into your tuning software? Bump your idle up 50 RPMs and see if that makes a difference.
It will smell at idle especially if you don't have CATs, even with a cam like that. I have a 226 222 116lsa cam and it still stinks a bit.
10-03-2007, 08:28 AM
#3
TECH Resident
Thread Starter
Thanks for the reply. I'll log idle FTC tonight. Although I think its in FTC #20 at idle. So that could be my problem then. My TPS (SAE) is 0% and measuring about 0.46v. So the car should thing its in idle. the timing looks like its in idle too. I'll check the FTC later.
The VE was tuned via WB, and i tuned the MAF a few months back before heads/cam. But my WB was showing lean when I let it idle for a few seconds, so I just bumped them cells in the VE table to see if it would bump up the WB reading, but it smells rich and didn't really effect the WB reading. However the WB reading looks great elsewhere. Its probably all down to the fuel Trim Cell.
The VE was tuned via WB, and i tuned the MAF a few months back before heads/cam. But my WB was showing lean when I let it idle for a few seconds, so I just bumped them cells in the VE table to see if it would bump up the WB reading, but it smells rich and didn't really effect the WB reading. However the WB reading looks great elsewhere. Its probably all down to the fuel Trim Cell.
10-03-2007, 11:46 AM
#5
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Nose calibration is iffy.
When you say it smells rich, you are likely talking HC fractions.
These rise faster and earlier going lean, than going rich (see
chart). Mildly over-rich, you get mostly CO which does not
smell. Stinging, that's NOx which also comes in more to the
lean side. So sweet-and-sour would be definitely lean while
sweet and dead, is rich.
Other thing is, you are not smelling a single continuous state
of combustion. You have the PCM swinging it from lean to rich
and back, all the time, in closed loop. Stock, it's quicker and
tighter. Slow down the O2 response and the proportional fuel
scheme and overshooting STFTs tend to "bury" the mixture
lean/rich/lean instead of staying tight to center. So you can
get a chunky stew out the pipe that has all three nasties in
it, the pipe averages the rich-nasty and the lean-nasty and
the WBO2 sees the blend, tells you not much about the end-
points and what portion of time you are there instead of at
stoich.
If you had your very own expensive 4-gas analyzer you could
tell about that, 2 of three means you're offset and all three
elevated means a cylinder-cylinder mixture imbalance ot a lot
of over/undershoot. But thousands of dollars for a low-use
tool, that's not in my hobby budget.
Probably the best thing to judge by, is the NBO2 waveform.
It's fast, unfiltered and if it's triangular, great; square but
fairly fast, OK; uneven looking, probably fuel over-swing is
your number one problem (whether from prop fuel or just
sensor lag).
When you say it smells rich, you are likely talking HC fractions.
These rise faster and earlier going lean, than going rich (see
chart). Mildly over-rich, you get mostly CO which does not
smell. Stinging, that's NOx which also comes in more to the
lean side. So sweet-and-sour would be definitely lean while
sweet and dead, is rich.
Other thing is, you are not smelling a single continuous state
of combustion. You have the PCM swinging it from lean to rich
and back, all the time, in closed loop. Stock, it's quicker and
tighter. Slow down the O2 response and the proportional fuel
scheme and overshooting STFTs tend to "bury" the mixture
lean/rich/lean instead of staying tight to center. So you can
get a chunky stew out the pipe that has all three nasties in
it, the pipe averages the rich-nasty and the lean-nasty and
the WBO2 sees the blend, tells you not much about the end-
points and what portion of time you are there instead of at
stoich.
If you had your very own expensive 4-gas analyzer you could
tell about that, 2 of three means you're offset and all three
elevated means a cylinder-cylinder mixture imbalance ot a lot
of over/undershoot. But thousands of dollars for a low-use
tool, that's not in my hobby budget.
Probably the best thing to judge by, is the NBO2 waveform.
It's fast, unfiltered and if it's triangular, great; square but
fairly fast, OK; uneven looking, probably fuel over-swing is
your number one problem (whether from prop fuel or just
sensor lag).
10-03-2007, 12:06 PM
#6
At best.....
4 or 5 gas is the shiznit. We use a 5 gas. Talk about "seein the light!"
Another very good point. 02 activity, and the min and max values are very important. Regardless of smell, active 02s, with nice quick swings from low to high and back indicate stoich. Jagged patterns with peaks and valleys that dont swing fully from say .900v to .100v indicate a cylinder miss.
If you had your very own expensive 4-gas analyzer you could
tell about that, 2 of three means you're offset and all three
elevated means a cylinder-cylinder mixture imbalance ot a lot
of over/undershoot. But thousands of dollars for a low-use
tool, that's not in my hobby budget.
tell about that, 2 of three means you're offset and all three
elevated means a cylinder-cylinder mixture imbalance ot a lot
of over/undershoot. But thousands of dollars for a low-use
tool, that's not in my hobby budget.
Another very good point. 02 activity, and the min and max values are very important. Regardless of smell, active 02s, with nice quick swings from low to high and back indicate stoich. Jagged patterns with peaks and valleys that dont swing fully from say .900v to .100v indicate a cylinder miss.
10-03-2007, 12:31 PM
#7
TECH Resident
Thread Starter
Attached is my latest log, perhaps this will shed some light on it. At the end there is some parked idle.
The HPtuners .CFG I have renamed to .TXT so I could upload it.
Driving the O2's are switching, yet idle they stay pretty much static.
The HPtuners .CFG I have renamed to .TXT so I could upload it.
Driving the O2's are switching, yet idle they stay pretty much static.
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10-05-2007, 09:13 PM
#8
try keeping it in open loop and lean it out until it runs smooth...that will be the correct a/f ratio. Trying to make these things idle by using a/f gauges can drive you crazy. I have ls1s running without 02 sensors and without cats and the exhaust does not smell of gas at all...If you smell fuel it is too rich no matter what your sensors say. Chuck
