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Closed loop and open loop.

Practical Reflash Tuning

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Don't fully understand.. so the car will be in closed loop mode in idle or low load driving and steady state driving and trying to get a afr of a stoich which is 14.7 pump gas, so it wouldn't matter what you set the stoich afr at? So at steady driving the ecu will make compensations of the current afr reading to get it to 14.7... what if you adjusted the maps at that area already close to 14.7 or at 14.7? Will this only happen if the temps change?? Somebody please chime in..


So yeah, a lot of thing can induce variation to the AFR, altitude, pressure, humidity, temperature... so working in close loop ensure that the AFR will be stable at 14.7 (usually defined by the close loop target table). The ECU will add or substract fuel using the feedback of the O2 Sensor to stay on target.

When tuning by reflashing a OEM ECU, there are 2 approaches. Disable the close loop system and adjust MAF calibration or fueling as close to our target as possible, then re-enable the close loop system when we are done so it account for the small AFR variation. The other method is to use the feedback of the close loop system to make sure we are on target (Short Term Fuel Trim + Long Term Fuel Trim). Which one you will use depend of the car you are reflashing, and personnal preference. If you look at the Subaru FA20 DIT engine, you can even tune WOT with the close loop system still enabled.

Hope it helps,


Thanks for the reply. Yeah that helps a little bit.. im going to be tuning my 1995 honda accord ex. F22a head with f23a block. With a turbo kit. So my question is, before I make any changes to any fuel cells or timing cells I first go into the settings and disable closed loop and then make my adjustments then before reuploading the map to the ecu, enable the close loop function then upload? Sorry, as you can see i have no tuning background what so ever.. lol. This all was a foreign language to me when I first started seeing the fuel tables and what not a few days ago.. lol.. and for handata s300, they use not percentage or lambda value for there fuel cells.. its at a not decimal value of two through five digit numbers.. how would I find out what exact number to put in a certain cell like hondata kpro where I can find the exact afr number and just type that into my cell and get results from that. Sorry again for all questions.. trying to hurry on my lunch break.. 🤣 🤣

Ok, so to answer the first part of your question :

You would need to disable the close loop for the entire fueling tuning process. That could be many reflashes. Once your fueling will be accurate in open loop, you can now activate the close loop. I usually enable the close loop when I take the car off the dyno, before the road test. If you follow the step process outlined in the Pratical Reflashing Course, you will see that you need to do a basic config of the ECU before starting to tune. This is where you would disable close loop.

For the second part, I have no idea, I’ve never used Hondata or tuned a Honda. So I don’t know about those 2 to 5 digit fuel value.

Ok, that puts it into more perspective for me.. I just need to remember to enable the close loop when I'm done tuning my afr's and basically stop adjusting the tables then turn it back on.. sounds easy enough. I'll figure out the whole 2 to 5 digit deal with hondata s300.. as long as I can use the lambda overlay feat. And lambda target feat to adjust my tables I think I will be fine. This is what I gathered from watching the lessons so far, I would download a default map to get started, then go into the settings and set all the things I needed to set like bigger injectors, disable closed loop. Set my gear ratios, and set my target lambda for pump gas. Then I would disable things I wouldn't need. Go into my fuel and ignition tables and data log my car on every load range possible, then adjust the afr's to what the target lambda is telling me to set them. With ignition im thinking I should leave it at the settings they are at. If I need to pull timing in some areas that seems to cause knock then do so. Once I am done tuning the tables and ready to disconnect re- enable closed loop. Its hard to believe but I have watched the first course and second course twice already and I just have a hard time understanding things is all.. I know it might not seem like I watched them, but I have and im taking my time with the third course for reflashing.. im all the way through to where its on work examples.. I know.. I know.. im a little dumb. But I will figure this stuff out even if I have to keep watching the videos a million times.. this is something I would love to learn and actually put into use for my love and passion of cars

So closed loop the ecu operates on the wideband or narrow band thats hooked up to the car. Open loop the ecu will run on the fuel maps and not go off of the wideband/narrow band. Why does this happen? Why can't the ecu just run on the fuel maps like open loop?.. wouldn't it be less complicated? But i think I'm starting to understand a bit of what closed loop and open loop means.. there is or should be a way to set when closed loop stops and open loop begins?

I just Google open loop and closed loop.. I understand it now.. closed loop is there for emissions and fuel economy reasons.. if the ecu runs on open loop all the time, it would guzzle gas.. open loop is there for acceleration and doesn't require fuel efficiency.. so it runs off of the set fuel maps tuned for it.. and rely on other sensors as well as closed loop, MAP ,intake air temp, humidity, engine temp.. all factors in while in closed loop to result in best fuel economy. Apologies for all the questions, just really excited to learn how to tune my car. Will do my best to try and learn from the video lessons, but with reading on open and closed loop, I was able to understand right after I got done reading the description. Like I was saying. Im a slow learner/ see for example type of learner, or i need to be hammered the information in a way I understand, like talking one on one with a tutor or the information is pointed out to me for me to read and if I don't understand by reading, then i just don't get the phrases used or words don't make sense to me, or don't know the clear definition to them.

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