Open vs Closed Loop Running
#1
Member
Thread Starter
Open vs Closed Loop Running
Been tuning in open loop and just went back to closed loop. While it runs OK and is more fuel efficient it idles much worse when cold with major loping. I'm failing to see much of an advantage to closed loop. Not running CATs so that's not a concern. Seriously thinking of just leaving things in open loop and screw the trims. So, anyone else running open loop permanently? ... and why/why not? (383 Xfire, renegade, mild cam upgrade, aluminum heads, EBL, long tube headers, VRFPR, Pprallel plummed, 90# Injectors, 700R4 )
Last edited by Cartrax; 07-22-2020 at 09:19 AM. Reason: asked for more feedback
#2
Supreme Member
iTrader: (16)
Re: Open vs Closed Loop Running
Originally Posted by Cartrax
Been tuning in open loop and just went back to closed loop. While it runs OK and is more fuel efficient it idles much worse when cold with major loping. I'm failing to see much of an advantage to closed loop. Not running CATs so that's not a concern. Seriously thinking of just leaving things in open loop and screw the trims. So, anyone else running open loop permanently? ... and why/why not? (383 Xfire, renegade, mild cam upgrade, aluminum heads, EBL, long tube headers, VRFPR, Pprallel plummed, 90# Injectors, 700R4 )
- Rob
#3
Supreme Member
iTrader: (20)
Re: Open vs Closed Loop Running
Cam can fool o2 readings at idle in closed loop sometimes but that can be compensated for. But doesnt sound like you have a huge cam so it shouldnt have a problem
no issues with keeping open loop all the time. Ive done it on many setups. Tune it to the air fuel and timing that the engine wants and runs best at. Dont focus on afr numbers necessarily
also what temp is closed loop enabling? If it runs bad when cold raise the closed loop enable temp
cold engines want richer mixes than typical closed loop stoich
no issues with keeping open loop all the time. Ive done it on many setups. Tune it to the air fuel and timing that the engine wants and runs best at. Dont focus on afr numbers necessarily
also what temp is closed loop enabling? If it runs bad when cold raise the closed loop enable temp
cold engines want richer mixes than typical closed loop stoich
#4
Member
Re: Open vs Closed Loop Running
I have been running an open loop tune for several years and am very happy with it. Closed loop was always a problem from idle to 1500 rpm's and I've never found a way to run richer in closed loop under 1500 but not over. Without cats I see no advantage to run closed loop. The EBL using WB VE learns lets you set the AFR where you want it at any rpm. Driving in stop and go traffic with a manual transmission is much more pleasant with a good tune. Fuel economy is also better with a happy motor.
#6
Supreme Member
iTrader: (16)
Re: Open vs Closed Loop Running
The EBL using WB Learns does in fact let you set the AFR wherever you want them, but you are not going to run in Learn mode on a constant basis, you are targeting a ten to fifteen degree area for everyday driving (eg; 190* to 205*, or 200* to 215*, etc), and the conditions constantly change. Both loop modes reference the VE table. The purpose of Closed Loop is "looped" O2 correction at idle as well as below the threshold of Power Enrichment, it's not meant to work hand in hand with catalytic converters. 14.7 is/was stoich, it is not a number that was referenced solely for a converter. You can easily set the targeted AFR in Closed Loop all the way down to 1.00 to all the way up to 25.50. Sculpting the VE to allow smooth idle and transition under commanded Closed Loop is just as easy to do as in Open Loop, because you are referencing the same fueling table that is being used.
... all we're doing is narrowing a range.
- Rob
... all we're doing is narrowing a range.
- Rob
#7
Member
Thread Starter
Re: Open vs Closed Loop Running
Thanks for replies. All very helpful, had to put this aside as I was wrestling with a nasty oil leak. Finally fixed with a new one piece Fel Pro oil pan gasket. Glad it wasn't a rear seal. Reviewing responses, I did temporarily set the open loop idle per RBob. Back on this now. Sounds like closed loop is best way to go once things are running well.
Trending Topics
#8
Supreme Member
iTrader: (1)
Re: Open vs Closed Loop Running
The EBL ..... You can easily set the targeted AFR in Closed Loop all the way down to 1.00 to all the way up to 25.50. Sculpting the VE to allow smooth idle and transition under commanded Closed Loop is just as easy to do as in Open Loop, because you are referencing the same fueling table that is being used.
... all we're doing is narrowing a range.
- Rob
... all we're doing is narrowing a range.
- Rob
While I'm sure you can do "learns" at any AFR you like if you are using a WB learn setup, this will not translate to closed loop operation at other-than-stoich AFR's as that is not within the capabilities of the EBL. It would be a nice feature if it could be added (I don't know if it's possible due to memory or processing limitations of the stock ECU upon which the EBL is based....). If you want closed loop operation that deals directly with a WB, you have look outside the EBL for that feature - some standalone ECU's can do it (such as the LINK ECU that I run).
GD
#9
Supreme Member
iTrader: (16)
Re: Open vs Closed Loop Running
Originally Posted by GeneralDisorder
The EBL is not capable of "closed loop" at anything other than 14.7...
Originally Posted by GeneralDisorder
... because it is not capable of using a WB for closed loop operation.
Originally Posted by GeneralDisorder
The stock NB sensor is only accurate at 14.7...
- Rob
#10
Supreme Member
iTrader: (1)
Re: Open vs Closed Loop Running
NB sensors only read accurately at stoich. If that were not the case there would be no need for WB sensors. They are designed for dithering closed loop at stoich - nothing more. You may be able to shove that around a bit - half an AFR point or so. But it becomes very inaccurate quickly.
And many standalone systems ARE capable of closed loop WB targeting. With or without dithering for a converter. Just not the EBL or any other stock ECU based systems. If you haven't experienced non-dithering closed loop WB control you should check it out. It dovetails nicely with WB learning, etc. This technology has come a long way in the 30 years since the stock computers were "high tech".
Also - Ethonol blends have a lower stoich. E15 has a stoich of 13.8, and E85 has a stoich of 9.7
The NB sensor only reads *accurately* at stoich. Whatever that is for your fuel blend.
GD
And many standalone systems ARE capable of closed loop WB targeting. With or without dithering for a converter. Just not the EBL or any other stock ECU based systems. If you haven't experienced non-dithering closed loop WB control you should check it out. It dovetails nicely with WB learning, etc. This technology has come a long way in the 30 years since the stock computers were "high tech".
Also - Ethonol blends have a lower stoich. E15 has a stoich of 13.8, and E85 has a stoich of 9.7
The NB sensor only reads *accurately* at stoich. Whatever that is for your fuel blend.
GD
Last edited by GeneralDisorder; 08-06-2020 at 10:57 AM.
#12
Member
Thread Starter
Re: Open vs Closed Loop Running
I see there are some difference of opinions - eh, makes the world work. Anyway after some PC glitches I'm back on this and going for more "tune" in open loop. Thing is I need a better understanding of how things work in open loop. So, some basic questions - What is the ECM looking at for fueling during open loop - just the AFR table? Does the VE table influence the AFR in open loop? How do these two tables play into one another in open loop if at all? The WB VE learn corrections I'm getting in open loop are a result of just comparing the afr tables to wb afr reads?
I know questions may be redundant but you can see my confusion and I'll never get this right without understanding what's going on. Thanks.
I know questions may be redundant but you can see my confusion and I'll never get this right without understanding what's going on. Thanks.
#13
Supreme Member
iTrader: (1)
Re: Open vs Closed Loop Running
In open loop there is no feedback. It uses the VE table and the AFR just is what it is. The ECU doesn't care or attempt to change it. There are no fuel trims applied - it just looks up a value for injector pulse width and fires the injector.
The AFR table is used for VE learns.
GD
The AFR table is used for VE learns.
GD
#14
Supreme Member
iTrader: (20)
Re: Open vs Closed Loop Running
Imo every tune should start with an open loop tune. Get the ve table correct. Do it at engine normal hot temp.
then cold start tune the open loop vs coolant temp to slightly richer when cold then taper off til it reaches operating temp.
then go closed
then cold start tune the open loop vs coolant temp to slightly richer when cold then taper off til it reaches operating temp.
then go closed
#16
Supreme Member
#17
Supreme Member
iTrader: (1)
Re: Open vs Closed Loop Running
Closed loop will just fight you while you are trying to create a proper VE table, etc. You want the BLM and INT (or fuel trims or whatever it's called on your particular system) locked to 128 (0%) while tuning. Get everything as close as possible in open loop, THEN turn on closed loop compensation.
GD
GD
#18
Member
Thread Starter
Re: Open vs Closed Loop Running
In open loop there is no feedback. It uses the VE table and the AFR just is what it is. The ECU doesn't care or attempt to change it. There are no fuel trims applied - it just looks up a value for injector pulse width and fires the injector.
The AFR table is used for VE learns.
GD
The AFR table is used for VE learns.
GD
#19
Member
Thread Starter
Re: Open vs Closed Loop Running
The following users liked this post:
Cartrax (08-09-2020)
#21
Moderator
iTrader: (1)
Join Date: Mar 2002
Location: Chasing Electrons
Posts: 18,409
Likes: 0
Received 217 Likes
on
203 Posts
Car: check
Engine: check
Transmission: check
Re: Open vs Closed Loop Running
Answering my own question as I'm digging... In open loop - "It does use the AFR table as part of the pulse width calculation. The lower the commanded AFR, the larger the PW." RBob So VE tables and AFR command table both play into fueling... That means in open loop the ECM does "trim" based on the AFR table???
PW = BPC * MAP * ~T * ~AFR * VE * DFCO * DE * BVmul + BVcor
~T is the inverse engine coolant temperature
BVmul is the battery voltage multiplier
BVcor is the battery voltage correction for the injector offset compensation.
If any of the other terms need further explanation let me know.
RBob.
Last edited by RBob; 08-09-2020 at 10:07 AM. Reason: TBI also has BV multiplier
The following users liked this post:
Cartrax (08-09-2020)
#22
Member
Thread Starter
Re: Open vs Closed Loop Running
Progress report - After some tweaks (moved SA table from RBob's 3006 Bin to mine wasn't a major change, adjusted SA and VE in idle zones to consistent values and set CTS to stay in open loop) I did three progressive WB learns. It has never run better. Had to watch breaking the rears with just a little throttle. All in all felt strong with 0 to 60 in under 6 without brake torqueing the 2500 stall.. It had been running fair but today... like I said the best. Thanks, for replies - now have a better understanding of what's going on with the variables. BTW - Funny how something like this affects your mood..
#23
Member
Re: Open vs Closed Loop Running
Been tuning in open loop and just went back to closed loop. While it runs OK and is more fuel efficient it idles much worse when cold with major loping. I'm failing to see much of an advantage to closed loop. Not running CATs so that's not a concern. Seriously thinking of just leaving things in open loop and screw the trims. So, anyone else running open loop permanently? ... and why/why not? (383 Xfire, renegade, mild cam upgrade, aluminum heads, EBL, long tube headers, VRFPR, Pprallel plummed, 90# Injectors, 700R4 )
Thread
Thread Starter
Forum
Replies
Last Post