open loop and closed loop fuel injection

 

This is Abdul from how efi works calm and today I want to right about fuel and AFR control there three ways we do this open-loop simple closed loop or PID open loop this is what no fuelling corrections are made by the ECU based on what we see from the wideband o2 sensor it's a little like setting your throttle stop on your car to say 15% throttle and then getting out on a flat road and for the most part you'll hold an even speed But if you get to an uphill or down your speed will change so now let's get into the settings of what it takes to set this up what I do is go to the fuel settings and down to AFR egao control and the algorithm in the upper left corner we are going to set to no correction if you notice the wideband o2 sensor is set up on eg o1 port so if we go ahead and start the motor running for a bit and look at the traces that we get you'll notice that the RPM is relatively Stable our AFR also is relatively stable I've got these zoomed way in so this is gone from 1400 to 1600 RPM and the AFR is going from about 12 to 15 so you can see that the AFR is quite stable I've got the o2 correction or the e GL correction as you can see the dance running flatline because we do have it turned off and at the bottom you can see that the pulse width is fairly stable so now let's talk about simple closed loop basically fueling Corrections are Incrementally stepped in based purely on if the last Oh to reading was Lena rich note that if you have a car with a catalytic converter the catalytic converter must see AFR readings oscillating above and below stoichiometric so let's go ahead and set this up what we do is again get into our AFR dgo control and we set it to simple we're gonna use ignition events in this example and I'm going to set that to ten we'll get to that in a Minute the controller step will step one percent at a time and I am going to use the Youth Authority table option you didn't see I've got this set up to only correct if the AFR is above ten point five or if it's below seventeen point five in my particular case that is the valid range of my o2 sensor and I'm going to bring it on if the water temperature is above 120 and the throttle is below 50% obviously I know all this sort of thing will be achieved The other thing I want to do is go to the eg o authority table and what this table does in my case today I've set it up for five percent authority around idle my motor idles right about here and what it will do is allow up to a five percent correction at high loads I happen to have itv loads set up on my motor and for the most part I generally run about ten percent when I'm out of the power so now let's see what happens once we've turned that on you can see That the idle has got somewhat more unstable compared to the way we were if you watch the AFR you'll see it come up down up down what that's doing is any time that the AFR goes lean on the lean side of switch the ECU will start incrementing in fuel until it sees its swing to the rich side as soon as it goes rich right here is the redline it starts incrementing down until it sees a lean condition again see do two swingley and it starts incrementing back each one Of these steps happens because we had it set up as ten ignition events down at the bottom you can see the pulse width changing around 1.9 or so you can see the pulse width oscillating up and down as the eg Oh correction swings in and out now when I zoomed way in this is one change in the egl correction and down at the bottom each one of these points is one full engine cycle of the motor so we have one two two-and-a-half engine cycles or ten ignition events so every Tenth ignition events one more increment will happen now we get the PID PID stands for proportional integral derivative it is when the fuelling Corrections are based on how far off the last oh two reading was from the target air farm and how fast the last oh two reading is approaching the target AFR down at the bottom if you type in sites.google.com / site / fpg aan d co / PID you can play with this stuff that's a cute little demonstration you can do But basically what this does is it predicts how much correction you're going to need in the future so now let's go ahead and set this up again we're in our AFR egao control page and i've said it taking the drag down and set it to PID and down here these are the PID settings which we won't get into today is - how to set these but those are the settings just like on that little practice demo page they give you a link to so now when you look at the engine Data you can see that the RPM has somewhat stabilized back even see how accurately the AFR is holding the correct answer in our case the target would have been the dashed line you can see the eg Oh correction incrementing slightly as it makes corrections and at the bottom of the pulse width is running and relatively stable open-loop is good if you happen to have like a race car running leaded fuel where it's going to be hard on the o2 sensors and you may Not have an option of running o2 sensors all the time simple closed loop is good if you happen to have a catalytic converter that quite as stable as PID but it gets the job done or of course we can always go to the PID control in a couple minutes I'll play a video from the racecar well you can watch all this happening but in the meantime I'd like to thank all my friends a tutor studio.com these are the guys that develop make a Log viewer HD which I used to generate most of these screenshots thanks for reading and be sure to hit subscribe on my youtube channel for you right foot we've escaped life quite suitable mouth