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Running without closed loop
Posted: Wed Jun 16, 2010 7:01 am
by msaunders
My S13 KA24DE runs in open loop cruising with a fairly stable ~14.xx AFR; however, once I enable closed loop the AFRs do the whole rich/lean dance and fluctuate AFRs inversely to the O2's voltage from about 15.5 to 13.9 AFR. I have read this is for proper operation of a catalytic converter and is normal, but in my case I don't have a cat. The fluctuations in this closed loop AFR seem to me like wasted fuel.
Are there any negatives if one ran without O2 feedback permanently?
Re: Running without closed loop
Posted: Wed Jun 16, 2010 6:19 pm
by HermaN
No, there are no negatives really. If the car is maintaining proper 14.7 on idle & cruise, then it will be no different, because that's what it should be aiming for with O2 sensing enabled.
However, that's interesting that it fluctuates in order to help the cat. Doesn't do it on any other turbo'd or N/A car I've seen, they always just seem to hovver around 14.7, but never dipping into the 13's then back up to the 15's. Sure your lambda sensor is working right? What voltages are you measuring from it? Should be between 0.1 - 0.9 volts if it's working correctly.
Re: Running without closed loop
Posted: Wed Jun 16, 2010 7:02 pm
by msaunders
The lambda voltage in the screenshot ranges from 0.04v - 0.95v. That seems about normal?
It's a simulated narrowband signal from an Innovate LC1 unit.
Re: Running without closed loop
Posted: Wed Jun 16, 2010 11:25 pm
by Bernardd
I've run open loop since 2000. No problems at all.
Re: Running without closed loop
Posted: Thu Jun 17, 2010 3:53 am
by Fordy
are you just disconnecting the sensor or unticking the feedback switch?
Re: Running without closed loop
Posted: Thu Jun 17, 2010 4:00 am
by KillerB
Oscillation is normal. Overshoot is a bit high but that could be due to lambda age (older and dirty means less responsive). I usually see afrs ranging from 14.1 - 15.1 when oscillating
Re: Running without closed loop
Posted: Thu Jun 17, 2010 6:07 am
by msaunders
Fordy - The top screenshot is open loop, O2 feedback bit unchecked and fuel maps set to 0 raw. Bottom shot is same setup with 02 on.
With the LC1 unit I have control over the simulated O2 signal...
Hypothetically speaking, I guess I could trim the rich/lean voltages to something more close together; say, .3-.7v and still have .5v cross at 14.7. Perhaps this will lessen the oscillation in AFR while in closed loop.
Does the ECU look for a certain min and max voltage from the lambda sensor?
edit-scrap that. tried it, doesn't work.
open loop FTW!