Open loop/closed loop

[Bermudablue]

In laymans terms.Could someone explain the differences.The pro's and cons
of each?....It would be much appreciated.

[35R]

Essentially Closed loop is when the engine computer is taking feedback from the O2 sensors and making constant adjustments to fueling (to counter rich or lean conditions). Open loop is when that input from the O2 sensors is not "active" - because the sensors may not be operational as yet (they take a while to warm up) OR when Power Enrichment (PE mode) is active, such as at Wide Open Throttle (WOT).

There are tables and settings in your engine computer that govern how, why and when your engine transitions between Open and Closed loop.

[DaveHAT]

Good question Tony,

Is there a general consensus on which is "better" in regards to tuning or is it dependent on the car and application?

[Bermudablue]

Open loop is when that input from the O2 sensors is not "active" - because the sensors may not be operational as yet (they take a while to warm up)

I run open loop and what you say here makes sense.Takes a bit of time for my car to settle from cold start.Though in open loop fuel consumption is not too bad.So once warmed up(in open loop)do i end up the same as closed loop.
I am of the opinion that closed loop is better.Will i get a smoother start up
with closed loop.I am quite happy with my set up but i am lost to which one is better
Have your say Luke.I'd like to hear it.

[35R]

I think as Dave hints, there is no definitive "better" appropach.

I guess it is application specific.

and results are probably dependant on the tuner anyway

I run open loop and what you say here makes sense.Takes a bit of time for my car to settle from cold start.Though in open loop fuel consumption is not too bad.So once warmed up(in open loop)do i end up the same as closed loop. I am of the opinion that closed loop is better.Will i get a smoother start up with closed loop.I am quite happy with my set up but i am lost to which one is better

Are you saying your car runs in open loop all the time? and/or that a closed loop startup would be better?

As above i think O2 sensors just dont work cold.

I would hazard a guess your cold start issues could be resolved otherwise.

[Bermudablue]

is it dependent on the car and application?


Well put Dave..I'm dead sure i got the best setup for my car but i do have the option of closed loop and i dont know what changes would occur.

Doug i am in constant open loop.What is the majority?

[bluess57]

From my previous experience with dodgy O2 sensors, the pcm will not use feedback from the O2 sensors for 2(?) minutes from Cold start, and until coolant temp is above 80(?) odd degrees. I have exact numbers somewhere...

Is DFCO enabled in open loop?

[SSUte01]

Tony,

To be honest I wasn't going to comment because most of below is based upon my understanding and opinion, however since you asked for my opinion here it is.

My opinion is best summarised by Dave, each application (I assume we are talking EFI GM series setups here) will respond differently and the underlying rule is to find the 'sweet' spot for your setup ie use what works best.

My car idles in OL and is in OL up until 1200rpms and from there it is in CL.

For info, like Dunc said there are the times your LS1 (I think I'll remeber them all) is in Open Loop anyways, like above OL means the PCM is ignoring O2 readings for fuelling and using predetermined airflow models (MAF or SD which is impacted by IAT and ECT also)

- Cold Engine Coolant Temps (ECT) at normal Sydney Intake temps (IAT) ie ~20*C a VY will enter closed loop at a low ECT of 34*, on a really cold morning ie if you parked overnight in a freezer (<-10) it will enter CL approaching 60*C ECT. This can be modified to suit your car, they are std numbers for a VY. Also provided other requirements are met to enter CL. Point is it will not stay in OL for all that long during a cold start.

- Power Enrichment - AFR will (should) enrich based on a further amount of parameter and enter OL.

- Lean Cruise (if fitted/enable) - Again this is performed in OL; AFR should lean to commanded level to optimise economy during certain circumstances

- If one or both of your O2s are unplugged (LS1) the PCM will enter OL as a default

I may have missed some other occurrences of OL under normal conditions but I cannot think of them atm

To directly answer your question, setup will determine what is best. O2 sensors are very accurate at stoich (lambda of 1) but not so good anywhere else (hence they are disabled during lean cruise and PE) but they are heat sensitive and confused by cam overlap and reversion. For this reason it is why I choose to idle in OL because it gives me the most stable and consistent idle. I have tried full CL and full OL tune and to be honest when fuelling is close there isn't much difference.

So changing exhaust (not so much but to an extent), changing cam (especially a large one) will often (not always) cause your O2s to be inaccurate especially at low airflows.

The only concern for me in full OL is the potential for fuelling to move due to weather/atmospherics (I am assuming SD ie no MAF here) and some setups I have noted are particularly sensitive in key areas to even slight changes in fuelling ie ~1%. This is the only real drawback IMHO of full OL. My method for overcoming this is to calibrate the O2s just in the same method everything else is calibrated to suit. This is rather time consuming but thus far seems more reliable that OL in some trouble areas (not idle on my car - still OL there). Even with fuelling established with a good bias between impact from IAT and ECT it can still be sensitive and this is where the O2s (or MAF for that matter) can be useful.

Will you get a smoother start up with closed loop, answer in my mind is, not necessarily, maybe you will or maybe you wont. Perhaps the best way is to try both and find out. The issue I personally have with cold start is you really only get a couple of shots per day to really test your findings. It sounds as though if fuel consumption is the same once warm then your fuelling has been setup very well - if I may can I ask what you mean by 'settle down' remembering that a non-stock setup will never be quite as good as stocker, there is always some compromise even if it is small.

The other time that O2s can be useful in this situation in my opinion is if you live in quite varying climate or your setup suffers badly from heatsoak as both can affect fuelling to quite some extent and therefore the O2s act as constant ability to account for this (once calibrated for those airflows)

Bottom line, closed loop is not necessarily better, but does have some advantages, some of which listed above, namely versatility and ability to account for fuelling anomoies. This big disadvantage is that they struggle at low airflows when stock O2s (and settings) are used on a non-stock (esp cammed) setup.

There is more than one way to skin a cat, so to speak.

BTW - DFCO if enabled will function as setup in both OL or CL

Dave,

Which is better - like you say application dependant. To generalise, if the O2s are unreliable for fuelling at a given airflow on a particular setup and cannot be calibrated to compensate, then OL is likely to be suitable under those conditions. That is about as general as I can be.

This is my opinion only so take it for what it is worth.

Hope that helps

Luke :)

[35R]

good post Luke, excellent contribution.

[Bermudablue]

A great post Luke and explains to me somewhat why my car is set up the way it is.
I have the utmost confidence in my tune,and dont want to change a thing.It was never in doubt.Its just a question.The car drives beautifully behaves well in traffic and is ready for a sub 12 come Sunday:yep:.It has nothing to do with politics Luke,just me wanting to learn a little bit about why things are done the way they are done.No doubt i will read your post many times over as i suspect others will.

cheers mate

[SSUte01]

I wasn't suggesting you were inferring 'political agenda' or anything other than a question. I should clarify that what I meant was that I generally reserve my opinion in matters due to people taking them the worng and missing the point of these forums - to help each other out and learn to get ahead vice push others down (personal sook of mine). I kow it sounds a little touchy-feely, but I truly believe that if we (try) and help each other out then we will all be more successful than the alternative.

So dont read too much into the 'political' comment, I simply meant I try to keep most opinions to myself unless asked or I think I can help that's all

In fact I will re-write that sentence to better convey my point

Luke :)

[Bermudablue]

And here i am sometimes worried to ask a question for the exact reasons you have stated.And all i want to do is learn.Its all good Luke thanks for your input:)

[NickS]

No doubt i will read your post many times over as i suspect others will.

:yep: ... 3 times now, and I still don't understand it ... :lol:

Great post Luke, the more I read about tuning the more I am convinced that I would rather leave it to others, you guys that have figured this stuff out impress the hell out of me.

:cheers:

[RedVYIISS]

:yep: ... 3 times now, and I still don't understand it ... :lol:

Great post Luke, the more I read about tuning the more I am convinced that I would rather leave it to others, you guys that have figured this stuff out impress the hell out of me.

:cheers:

What he said!!!

And what I find particularly impressive is watching someone who knows what they're doing sort out a tune (I've sat through watching cars being tuned by both Sonny and Dale). Sonny has tuned my car when it was n/a (a mafless tune), then did the 2 bar mafless tune for my turbo setup. Both times I sat beside him and watched the entire process. The turbo tune was particularly interesting as I expected him to pull a previous customers turbo tune to use as a base, then modify it. He didn't!

The car had a 'rough' safe tune in it that allowed me to drive it to Sonny's workshop, he then proceeded to enter 100's of table setpoints from data that he had stored in his head! He then stated the car and ran it up on the dyno and the 'real' tuning began. I can't remember how many dyno pulls, with adjustments after each, then on the road checking part throttle, cruise, full throttle (difficult given location and speed attained very quickly!).

I guess it took the best part of a long day (it happened over two sessions as I had to add a second fuel pump, 1 pump couldn't supply enough fuel). I'm sure a good home tuner could get similar resuts and ultimately a tune as good as mine, however I suspect that it would take many, many hours to get close and many more to get as good a tune.

I found it very interesting to watch the process and have contemplated buying the tuning software to allow me to monitor and log the car, however I'd never be game to attempt to 'improve' on the current setup.

[scat2k3]

This is a great thread with lots of good info guys. :bravo:

Thanks quicksilver for asking the question and never be afraid to ask anything on this forum. Any car, any track.........any question :lol:

I'm like Nick & Al, no idea but it's threads like these that give you an idea just how much is going on when you fire up the engine. The stock GM PCM is a pretty sophisticated bit of kit.

Am I right in saying that a 2bar tune is like having 2 tunes? One complete tune for off boost and one complete tune for when the thing is making boost?

Cheers,

Scott

[NickS]

Am I right in saying that a 2bar tune is like having 2 tunes? One complete tune for off boost and one complete tune for when the thing is making boost?

Cheers,

Scott

That's pretty much the way I understand it Scott, so much changes when you hit boost that you can't really have one set tune running everything at it's optimum all the time, so 2 bar tunes allow you to adjust between boost on and off.

I did the same as you Allan, sat next to Sonny during the whole tune, must have been 8 hours I reckon. So many numbers, so many adjustments, so many dyno runs. Sonny then took it for a drive while I held the laptop, he then reviewed a bunch of stuff and proceeded to continue making adjustments while I drove around for another 45 minutes or so.

Very impressive ... :yep:

As for Luke, Dunc & Erik ... Sonny does this for a living, you guys ... wow.

[35R]

usually a 2 bar tune is a custom operating system (with support for a 2 bar MAP sensor, higher range VE table and boost enrichment parameters)

[RedVYIISS]

usually a 2 bar tune is a custom operating system (with support for a 2 bar MAP sensor, higher range VE table and boost enrichment parameters)

yep, what Dunk said.

The std MAP sensor measures between -100 kPa and 0 kpa gauge (MAP sensor measures manifold absolute pressure, -100 kPa gauge is approx 0 kPa absolute, no manifold will ever see such a low pressure). A 2 Bar MAP sensor measures from -100 kPa gauge to +200 Kpa gauge.

For a 2 Bar tune, the fueling/timing etc is conststantly adjusted by MAP (manifold absolute pressure) for all pressures that the inlet manifold sees, in my case a small negative pressure at idle, through to positive 70 odd kPa. So in short, the tune is not adjusted for 'on boost' and 'off boost', it is adjusted for all pressures seen in the manifold from slightly negative to positive 70 kPa and all pressures in between..... an enormous number of combinations are possible.

BTW, 100 kPa = 1 Bar

I'm sure one of the tuners will correct me if any of that is wrong!

[10sec_rx7]

the 2 bar reads from -100 to +100 AL,

or 210KPA totall

[RedVYIISS]

that'd explain why it's called a 2 bar MAP sensor! (-100 to +100 kPa = 2 Bar range)

[Delft Maloo]

good post guys. some of you may know and some not but luke has been helping me with my tuning( teaching me to use my software). there certaily alot in their and it takes time to learn but once put into practice it comes to you. im getting there slowly but steadily and it makes things alot easier if someones willing to help. dont be afraid to ask q's cause if you dont ask you wont know, and for those who like to laugh at others for the questions posted wether they be dumb or brilliant you can go and :flip1: . just cause somone doesnt know what you might it doesnt give anyone the right to try and flame them, cause truthfully i doubt youd have any idear either:yep: .

this last part was in no way directed at anyone who has posted in this thread.

[RedVYIISS]

And I'm hoping that nobody takes my post as knocking home tuners, infact I think the opposite is true, though I'm sure it's not for everyone. I'm also quite sure that starting your learning curve on a forced induction car would likely end in tears!

[SSUte01]

I guess I should have noted the other obvious advantage of Open Loop is that it allow you to command any conceivable AFR under almost any condition. These engines dont always run their best at stoich (aside from max power/torque I mean) and this is where OL comes into its own.

[BigKahuna]

Theres some very valuable information posted in this thread.
Lets hope that it continues.

:yep:

[oztrack]

My car is in open loop but its able to be in semi closed loop. All i need to do is specify 14.63 and it uses the O2 sensor to give short term trims. It doesnt have long term trims that might let the tune drift.

I have barely changed my tune since May last year for drag racing. The main VE table and timing are very similar street/strip, Only the recent mods have created a need for change.

[Bermudablue]

What causes a tune to "drift" I read from Steve's post "long term trims"
Does this happen in open loop?

[oztrack]

Long term trims are an average over a certain zone. All it takes is one cell to be repeatedly incorrect eg rich and it could cause the entire zone to become lean to correct the effect that incorrect cell has. It can cause problems but is meant to prevent them.

It can be your friend but with a cammed car it could cause the tune to drift.

Its nice to have a tune that can cope with all weather conditions and not have it move somewhere of its own.

[35R]

What causes a tune to "drift" I read from Steve's post "long term trims"
Does this happen in open loop?

Here's a little light read from the HPTuners help file

http://www.trackchat.com.au/Duncan/VE.pdf

[Bermudablue]

Here's a little light read from the HPTuners help file

:shock: A light read...lol...I'm getting in over my head.I didnt understand a fair bit of that but it did answer my question....Do you have another
"light read" link on closed loop just to mix me up even more?