civictypenos

just looking for a good explanation of what these terms mean,i keep hearing them but dont really understand what they are.i know it has something to do with the ecu programming.

im using a vafc and wanted to know how it effects the ecu in closed loop and open loop.

Mase

Closed loop is simply when the ecu uses o2 feedback

Open loop is when the ecu does not use the o2

Killer_B

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase &raquo;</TD></TR><TR><TD CLASS="quote">Closed loop is simply when the ecu uses o2 feedback

Open loop is when the ecu does not use the o2</TD></TR></TABLE>

i assume that Full Throttle is "Open Loop", right?

civictypenos

so,my wideband reads 14.5 at idle,no matter what adjustments i make on the vafc.thats closed loop right.or when im on the highway,about 35% throttle,it reads 14.5-14.7,its in closed loop then?i dont have control over it right?im just curious because i see these things and couldnt really explain them to my self.

egturbo

does it have to do with vtec??<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase &raquo;</TD></TR><TR><TD CLASS="quote">Closed loop is simply when the ecu uses o2 feedback

Open loop is when the ecu does not use the o2</TD></TR></TABLE>

ScrapinSi

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by egturbo &raquo;</TD></TR><TR><TD CLASS="quote">

does it have to do with vtec??</TD></TR></TABLE>

No... Open loop is where your ECU uses all of the sensors to adjust the air fuel ratios...

Closed Loop is where the ECU uses its preprogrammed maps and works off of those, and doesn't adjust as much

95c1v1cs1

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civictypenos &raquo;</TD></TR><TR><TD CLASS="quote">so,my wideband reads 14.5 at idle,no matter what adjustments i make on the vafc.thats closed loop right.or when im on the highway,about 35% throttle,it reads 14.5-14.7,its in closed loop then?i dont have control over it right?im just curious because i see these things and couldnt really explain them to my self.</TD></TR></TABLE>

I'm in the process of trying to figure this all out myself. I have done some of the same experiments as you with changing the figures at idle and it automatically changes them back to 14.7. This is because of Closed Loop. The O2 sensor is changing it back to that point i am assuming.

I think after a certain point it changes to open loop and you are in control of the fuel being put in. I think it is at around 4500 or at WOT.

Its kinda scary when you are running boost at like 3500 and airfuel is sitting at 14.7. But I haven't figured anyother way to fix that other than to get a standalone.

I hope to get some more insight on this...

Corey

Johnyquest

The computer goes into open loop beyond 70% throttle, or whenever it detects a quick and drastic change in the TPS. Closed loop uses the o2 sensor feedback and hovers the a/f ratio around 14.7 for maximum fuel mileage and efficiency. This is safe for highway cruising and low load conditions. Open loop is at full throttle or brisk accelaration, and this is what you can tune. In open loop, the ecu will control fuel no matter how you set the afc (unless you go TOO out of whack, then it loses control, but this just ***** things up, you CANT tune open loop). That's why I tell everyone to set their afc hack hi/lo map changeover to 70%/71%. This is because below 70% the comp tries to adjust everything, so you just find a comfortable setting for the ecu to work with and let it do its thing. Then you can just adjust the high throttle maps for full throttle boost and not **** with the low throttle while your at it. There really is no way to tune closed loop. I suspect this isn't unsafe even when we are boosted, since we are running 93 octane and the computer really is only in closed loop under low load conditions. Usually when your really accelarating hard, the thing goes into open loop anyways.

95c1v1cs1

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Johnyquest &raquo;</TD></TR><TR><TD CLASS="quote">In open loop, the ecu will control fuel no matter how you set the afc (unless you go TOO out of whack, then it loses control, but this just ***** things up, you CANT tune open loop). </TD></TR></TABLE>

Do you mean in Closed Loop?

BigMoose

Johnnyquest got it mostly right. So to add a little variety, let me take it from a different direction.

The terminology open and closed comes from the instrument and control discipline. Where things like control are done with servo loops. When we have a good signal from the result we are after we "close the loop" with that signal in an error amplifier and use that error to dither control parameters to get that error to zero.

Now about emissions, no matter what anyone else tells you, BigMoose is telling you that our 3 way catalysts have negligible conversion efficiency when the exhaust stream is about 0.15 fuel air ratio above or below stoichiometric. Thankfully our little friend the cheap, yttria stabilized zirconia oxygen sensor goes bipolar right at stoichiometric. So we use his signal as an imput into our ECM error amplifier to "close the loop" and get the error to zero.

Now we all also know that stoich is not the best power point. So if our power pedal wants more than about 70 to 85% peak power, we then need to emit copious amounts of carbon monoxide. Hence we take our o2 sensor out of the loop, and "use every sensor available" to map into predefined engine fueling maps. These maps determine the injector PWM on percentage and hence fuel delivered. Under these conditions we are running open loop.

Now in reality closed loop usually starts off with a baseline map to get close, then the oxygen sensor dithers a correction map, or trim map to bring things into register.

Hope this helps some, it was fun writing it twice..... cause i erased the first response by accident. .... darn computers. I wonder why any can last over three months with me, considering how often I throw them at the wall! .... dave, step away from the keyboard, your congnac is calling.......................

civictypenos

NICE,im starting to understand,i might just have to read it a few more times.i dont run the hack,i just use my afc like normal for tunning,any suggestions there,with these loops in mind.

so i think that a good thing,my vafc only takes over at sudden exceleration and at wot right?

is there any way to meter when this actually takes place?the swictch between open and closed loop.