Idle fueling targets

[Ridgeracer]

What boostin posted is what I always observed on my WBO2...On occasions my car would dip lean towards 15 AFR and return to 14.3 at idle.

 

Someone do the same. Log AFR sensor 1, WBO2, and stft at idle.

[LittleBlueGT]

Awesome. Thanks for posting that.

 

All this time, I thought the feedback loop was just oscillating from too much gain, and I wanted to "fix" it.

 

Same here. I even (mostly due to post turbo front O2) skewed my front O2 scaling to stabilize it more.

[LittleBlueGT]

Does wonders for the smell and the idle roughness isn't bad if you retard the timing a bit.

 

I was just about to start digesting all those e-mails you sent me, and now you say on a lean mixture I should RETARD the timing a bit? I thought you advanced it a bit?

[Boostin1657615274]

Too much or too little timing advance will make the idle rougher. If you've ever used a timing light on certain older cars, you will notice that the idle will be rougher whether it's advanced or retarded from the timing mark on the pulley.

 

I'd also like to point out that I had idle stability problems when I started to lean out the idle closed loop AFR target. But there are two caveats to that: I didn't spend a whole lot of time on it... I think I set the target to 16:1, which is significantly leaner, and then when that made the car drive badly I just put it back to stock. And second, this car might need a slight MAF rescale just near the idle airflow range because the fuel trim there is over 10%.

[Ridgeracer]

I question the fact that leaning out idle and low load would help conserve fuel and maintain drivability on these cars. If it was possible, I think they would have already included it in the stock ROM calibrations...my .02 cents

[bugblatterbeast]

I was just about to start digesting all those e-mails you sent me, and now you say on a lean mixture I should RETARD the timing a bit? I thought you advanced it a bit?

 

it is a bit counter intuitive. because idle speed is closed loop regulated to a fixed rpm, the computer will open the throttle till there is enough torque output to maintain the target speed. with slightly retarded timing, you get less torque pulsation as the pressure peak happens later past TDC and there is less negative work done on the shaft (compressing a burning mix). the mean torque is the same (due to fixed speed) but the torque pulsation drops with a later ignition point.

 

there's a limit to the amount of retard you can dial in though. if you go too far the computer has to open the throttle so far that your torque pulsations increase because you are doing more work compressing a denser mixture.

[bugblatterbeast]

I question the fact that leaning out idle and low load would help conserve fuel and maintain drivability on these cars. If it was possible, I think they would have already included it in the stock ROM calibrations...my .02 cents

 

except that a factory tuned car needs to pass emissions. peak fuel economy tends to happen around lamda 1.1 not at stoich or richer. a TWC is pretty useless if the time averaged mixture is not stoich.

[Boostin1657615274]

I question the fact that leaning out idle and low load would help conserve fuel and maintain drivability on these cars. If it was possible, I think they would have already included it in the stock ROM calibrations...my .02 cents

 

http://www.legacygt.com/forums/attachment.php?attachmentid=81717&stc=1&d=1268438690

 

They can't run it much leaner than stoichiometric from the factory because of NOx emissions. Even on direct injected engines this is a problem.