closed loop/open loop

[rojizostang]

when should the pcm be in open loop?

when should it be in closed loop?

and what's the advantage or disadvantage to being/staying in one or another?

why would a tune stay in open loop?

 

[Hawgman]

When the engine is first started, and rpm is above 400 rpm, the system goes into 'Open Loop' operation. In 'Open Loop', the PCM will ignore the signal from the Oxygen (O2) sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal. The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. 'Closed Loop" is the normal operation mode of the PCM. In 'Closed Loop', the PCM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor.

Running the system in 'Open Loop' will ignore the O2 sensors and you can use that to "bandaide" out a lean running condition. But your fuel economy will suffer from it.

As for why a tune would stay in 'Open Loop'? First thought would be that the tuner wrote it that way. If not, then I would suspect a PCM issue.

 

[bigray327]

Great post, Hawg.

A specific amount of time has elapsed after starting the engine.

That time "delay" can be changed by your tuner. I found that my O2 sensors were not heating up in the standard delay time when I put in my long tubes (since they're farther downstream now), so my tuner increased the delay time. It worked.

 

[terry5357]

When the engine is first started, and rpm is above 400 rpm, the system goes into 'Open Loop' operation. In 'Open Loop', the PCM will ignore the signal from the Oxygen (O2) sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal. The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. 'Closed Loop" is the normal operation mode of the PCM. In 'Closed Loop', the PCM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor.

Running the system in 'Open Loop' will ignore the O2 sensors and you can use that to "bandaide" out a lean running condition. But your fuel economy will suffer from it.

As for why a tune would stay in 'Open Loop'? First thought would be that the tuner wrote it that way. If not, then I would suspect a PCM issue.

Damn Hawg! If I didn't know better, I would say you know what the hell you're talking about.........lol.

Great post, Hawg.


That time "delay" can be changed by your tuner. I found that my O2 sensors were not heating up in the standard delay time when I put in my long tubes (since they're farther downstream now), so my tuner increased the delay time. It worked.

Ray,
This is what Wes did with my tune....works great.

 

[rojizostang]

As for why a tune would stay in 'Open Loop'? First thought would be that the tuner wrote it that way. If not, then I would suspect a PCM issue.

i had trouble with slow o2 sensor codes. pretty much what you posted is what i thought, but didn't know for sure. i'm surprised that the tune was written like that, however. i won't go in to any sort of criticism though about this tune, or the tuner.

i do have one of the tunes form american muscle that goes into closed loop as it should. i think i'll reload that tune and see what happens. i've been trying to eliminate some slow throttle closing issues and never really looked at the real time data until recently. that's when i found the tune was staying in open loop and i was surprised by that, which is why i asked these questions to make sure i didn't have my reasoning backwards.

 

[Hawgman]

Damn Hawg! If I didn't know better, I would say you know what the hell you're talking about.........lol.

Well, considering how much shit I went through a couple of years ago with my car pulling fuel while reading lean and experimenting with different Open Loop scenarios, yea, I know a little bit about it. Not going to claim to be all smart and stuff... just saying I have been there and done that.

 

[terry5357]

Well, considering how much shit I went through a couple of years ago with my car pulling fuel while reading lean and experimenting with different Open Loop scenarios, yea, I know a little bit about it. Not going to claim to be all smart and stuff... just saying I have been there and done that.

I was just jacking with you.....lol. With the post that you made, I have no doubt what-so-ever that you know WTF you're talking about.

 

[rojizostang]

i was told that my car isn't in open loop. i was informed that my car's adaptive learning is off, hence the long term fuel trims show zero. i'm still a little confused though, because in the fuel menu while looking at the real time data, it says "open loop", while american muscle's tune says "closed loop".

what is the purpose for the adaptive learning to be turned off?

anyway, my lack of knowledge on this subject is the reason i won't say anything about the tuner.

 

[DirtyDogOfTheDesert]

It also goes into open loop at WOT.

 

[SilentScope]

hmm interesting.
so you can tune your car to always be in closed loop? not saying that ideal, but u can do it?

and good write up hawg

 

[rojizostang]

It also goes into open loop at WOT.

we're talking at idle. not brave enough to look at it at wot

 

[turbotr]

If you mean closed loop at WOT, basically no in our case with switching O2s providing the feedback. The regular switching O2s are designed and good for one thing only really- sensing stoich a/f ratio, by telling the PCM that the a/f ratio is either rich of stoich or lean of stoich. But it doesn't really tell by how much rich or lean. Thus the switching O2 closed loop control scheme is designed around that, generally known as a "ramp and jumpback" algorithm. As opposed to a basic linear control scheme with linear a/f ratio feedback (like in a FAST system for example). The FAST system (and others) can run closed loop at WOT, and that has been one of it's more important features for racers for years. Because it makes the WOT a/f ratio tuning process easy enough that it can be done in just a pull or two down the track.

I have a classic FAST on a turbo street car and really liked the fact that it can also run in closed loop with nitrous power adder for example. You get the added nitrous fuel close, on the rich side of your target, and let the closed loop fine tune it down to your target a/f ratio with nitrous on. I ran a target of 10.9:1 with 30 psi boost + 175 nitrous jet, C16 fuel. It worked great.

TurboTR

hmm interesting.
so you can tune your car to always be in closed loop? not saying that ideal, but u can do it?

and good write up hawg

 

[rojizostang]

back on topic, though the above posts are interesting, it's not what i'm really looking for. a more direct question is this: i was told that even though my datalogging says "open loop", this wasn't the case. the car was actually in closed loop (still talking at idle, i assume all they way thru the rpm range also) but just the adaptive learning was turned off.

is that possible? and if so, why does the read out say "open loop" if in fact it is closed loop? and, can the adaptive learning be turned off and still be in closed loop?

 

[lito]

back on topic, though the above posts are interesting, it's not what i'm really looking for. a more direct question is this: i was told that even though my datalogging says "open loop", this wasn't the case. the car was actually in closed loop (still talking at idle, i assume all they way thru the rpm range also) but just the adaptive learning was turned off.

is that possible? and if so, why does the read out say "open loop" if in fact it is closed loop? and, can the adaptive learning be turned off and still be in closed loop?

In some calibrations the open loop flag does not works as expected, for checking if you are actually in close loop look at the trims (STFTs), if they fluctuate (after the calibrated time and ECT/O2 temps) you are in closed loop, not mattering what is set on the adaptive switch.

 

[rojizostang]

In some calibrations the open loop flag does not works as expected, for checking if you are actually in close loop look at the trims (STFTs), if they fluctuate (after the calibrated time and ECT/O2 temps) you are in closed loop, not mattering what is set on the adaptive switch.

well, there ya go, that's what i was looking for. it seems the trims aren't moving at all. i mean stft and ltft. the ltft was set a 0 and the stft was set at 17...and not changing.

thanks. i'll do some more datalogging this week and playing around to be certain.