Force open loop just at idle

[RonSS]

Sorry if this has been covered before but I could not find exactly what I’m looking for in a search. What I’d like to do is keep the vehicle in open loop at idle say to about 1,200 rpm, then closed loop above that rpm. Working on an 02 LS1 Vette, OS: 12221588. Thanks.

[TAQuickness]

Welcome to the forum RonSS.

There may be a few ways to accomplish this. But first, could you tell us what you're trying to do by forcing open loop at idle?

[SSpdDmon]

Set the TPS% PE enabler to 0% for the lower RPMs and then you can have open loop at those RPMs.

[ringram]

Hmm, that wont force open loop unless you mess with some other stuff. It will however prevent PE and keep you in closed loop if you want.

Messing with open and closed loop is easier with the custom OS's which you should be able to run in your C5.

Do you have a scary cam to control?

[RonSS]

Guess I should have introduced myself before I started asking questions…. I’m just regular gear head that has been playing with Chevy’s for most of my life. Not new to making fuel and timing decisions on an engine I’m just used to 850 Holley’s and a distributor. Changing the cam on my Vette was no big deal, just work. Now getting it to Idle, that’s the hard part for me, there’s no mixture screws! Anyway thanks for your input guys….

After the cam (220/227 with 112 LSA) install I’m having trouble keeping the idle mixture correct. Keeps wanting to go rich. I can see why from looking at the live data, MAP knows the manifold vac. is kinda low, I think the cam has enough overlap at idle that a little O2 is getting pushed into the exhaust before the valve closes. The O2 sensors see that Oxygen so the voltage on the sensors starts to drop. Even the MAF sensor looks funny with the GPS all over the place. Bring the rpm up to about 1,200 and everybody is happy again, STFT’s go back to normal. I know there are many ways to attack this problem but the few things I’ve tried don’t seem to make much of a dent. I can adjust the VE table and that seems to help but eventually the PCM just adds fuel, trying to get the O2’s to cross. I have played with {B4115} to try and limit the amount of STFT adjustment but even that does not seem to work for very long. I know my biggest problem is my lack of experience but I’m learn’n. So I was thinking if it stayed in open loop below 1,200….. you get the idea.

[ringram]

Check out custom OS3 you should be able to flash that in and then flash your current tune over the top. Its pretty straight forward if you follow the tutorial. Then its easy to tell it to go open loop in exactly the RPM and MAP cells you want. You can then drop back to O2 trims from 1000 or 1200 rpm up etc.
Virtually the first thing I did when I got flashscan was dump the stock OS and install OS3. It has many more features to suit cams, forced induction etc.
Your issue will then be resolved

[Tordne]

So ringram.. You're suggesting running Semi-Open loop at selected points right? Sounds like a reasonable solution mate!!

[ringram]

Yeah open loop at idle, then closed loop either throughout the rest and use PE as per normal. Or use B3647 in OS3 as you see fit. SemiOpen loop as you say. (Just enter 14.63 where you want closed loop and anything but 14.63 elsewhere to go open loop)
Im sure there are other ways to do it. But thats the best IMHO then you can make best use of the flexibility of the OS.

[RonSS]

My current OS does not use {B3647}. If I load it over OS3 I’ll assume I still won’t have a {B3647} to adjust. That’s cool with me but do you have any other suggestions on a parameter I could adjust to force open loop? I did D/L OS3 for my OS and I did not notice anything in the EFI Live Custom Calibrations section that would let me decide open or closed loop. Thanks guys.

[Tordne]

Open Loop generally only happens when you go into PE mode or are below the Closed Loop enable temp.

Even with COS3/5 you won't be going into and out of Closed Loop. You would be running in Open Loop mode, and if commanding an EQ Ratio of 1.00 you will be in Semi-Open Loop which uses the O2's to trim. Subtle difference