Can someone explain to me......

[WiseGuyZ06]

when tuning w/open loop only, how does the MAF still influence fueling???

Im still trying to decide which way to go..

1. OLSD
2. MAF tune
3. OL tune

Which is the easiest way to tune the car???

The time is comming to decide....

[5.7ute]

Open & closed loop decide whether you are using NB feedback to adjust your fuelling where Speed density & MAF are ways to measure the airmass for the fuelling calculation. AS RHS said its like comparing apples with tractors.
You have four main options.
OLSD where you are measuring airmass by RPM/IAT/ECT/MAP
CLSD Same as OLSD with feedback from the narrowband o2 sensor.
OLMAF Which uses a hybrid SD/MAF calculation until B0120 is met where the calculation is taken purely from the maf.
CLMAF same as OLMAF with feedback from the o2 sensor.

[dfe1]

The "best" approach is at least partially dependent on the engine. There's no need to run open loop or speed density if the engine is stock or lightly modified. It won't hurt anything to use either of these protocols, but you'll have to spend more time to get the tune right because you've eliminated the self-correcting capabilities of O2 feedback and MAF control.

The primary benefits of open loop and speed density is that they eliminate the self-correcting capabilities of 02 feedback and MAF control. (Sounds like something a politician would say, doesn't it.) But in this case it actually makes sense, because if you're running a long duration camshaft or have some form of forced induction, the O2 sensors and MAF sensor may not be capable of supplying accurate data to the PCM/ECM. As an example, when a long duration camshaft is calling the shots, relatively high amounts of unburned fuel tend to enter the exhaust system. Being relatively simple devices, O2 sensors don't understand this phenomenon and simply react to what appears to be an excessively rich air/fuel ratio. If you run open loop, you eliminate this issue by taking absolute control of air/fuel ratio. But if an engine has a stock or mild cam, there's no need to run open loop unless you just want to go through the learning experience. (Which isn't a bad idea.)

[joecar]

The PCM uses the MAF and/or VE to compute the cylinder fill airmass...

Then the PCM determines what AFR it will command
(in CL it uses stoichiometric [trimmed by NBO2 closed loop feedback];
in OL it looks up the OLFA and/or PE tables and any other modifer tables)...

Then the PCM computes the fuelmass required to meet the AFR it is commanding...

Then the PCM computes the injector pulse width [from the IFR table] to spray that amount of fuel.


MAF/SD is mutually independent of ("orthogonal to") OL/CL... they are unrelated to each other.


MAF/SD determines how the airmass is computed;
OL/CL determines how the commanded AFR is obtained.

[SSpdDmon]

Another way to think about it is to dumb the process down to the basics. What is a loop? A circle or continuous process, right? If you open that loop, you disconnect that process and create a line. Perfect example, you pull a rubber band out of the drawer at home and cut it in one spot. Initially, it was a closed loop...until you cut it and open the loop. The same thing happens with our cars (in factory form). You start up the car and you're in open loop. Regardless of how the airmass is calculated (MAF vs. VE vs. blended), you're fueling is what it is and that's the end of it. The NBO2's could be screaming like a 2-year-old in a toy store and it won't matter. Once your ECT hits the threshold for closed loop (102*F IIRC), that rubber band is like new again and the PCM starts paying attention to what those NBO2's are saying. Based on their feedback, it starts tweaking the fuel trims so that the commanded AFR is in line with the observed AFR. If you're driving aggressively and surpass the PE TP% vs. RPM thresholds, you'll be back in open loop because PE is active. Only this time, the PCM might assume on occasion that what's commanded isn't accurate - and that's when you have positive fuel trims in closed loop. Based on what it knows to be true in closed loop, the PCM may add in those positive fuel trims in open loop just to be safe. Again, the NBO2's could be going crazy and the PCM won't care. It doesn't care because they aren't really accurate around any AFR much outside of stoich. Let off the gas and you're right back in closed loop...

MAF vs. SD on the other hand is basically what tables and sensors are used to determine how much air/oxygen is in the cylinders. In steady state, the MAF is said to be more accurate. But if the tables are tuned correctly and the sensors are working appropriately, either one should work just fine.

[WiseGuyZ06]

well.....

[joecar]

What car do you have (easiest way to tune is OLSD, then if you want MAF you tune that also)...?

[hquick]

Awesome explanation SS...thankyou.

[SSpdDmon]

No problem. :)

[WiseGuyZ06]

What car do you have (easiest way to tune is OLSD, then if you want MAF you tune that also)...?


Joe its a 2001 z06... Prob. gonna do a maf tune then when I get back up north ill do a OLSD tune.

[WiseGuyZ06]

Can someone tell me what do I do when I 1st start up the car If I wanna go the OLSD route down here in fl....

[dfe1]

Can someone tell me what do I do when I 1st start up the car If I wanna go the OLSD route down here in fl....
Pray

[dfe1]

Seriously-- When you say "What do I do"-- you don't do anything when you start the car. It all has to be done before then. My suggestion is to install a custom operating system, then do a speed density tune, then go to open loop. You'll find that you have to rework the VE table quite a bit when you switch to SD, so it's best to do that before throwing open loop into the mix. You'll need a wide band to get open loop operation calibrated properly. You can get close by getting your long term fuel trims within 1%, but that's really just an exercise because you'll have to go through the process again when you install a wide band, and you'll need a wide band to do heavy and full throttle calibration.

[WiseGuyZ06]

I have a wideband in the car... an lc-1