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 )

 

Depends on where you have your targeted air/fuel ratio. Open Loop will target 13.5 at idle, and Closed Loop will target 14.7. If you're running an Open Loop tune w/the EBL and tuned it via VE Learns, but then switched to Closed Loop, you would either have to tune that very Open Loop for 14.7 when fully warmed up at idle, or tune Closed Loop for 13.5 at a fully warmed up idle, so the two can correspond. Otherwise it will run horribly at idle when switching (eg; hunt, surge, etc.). There is no benefit to an Open Loop idle, and this is coming from someone with a big camshaft. Open Loop tunes are for members who simply give up trying to smooth out the tune at idle in Closed Loop...

- Rob

 

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

 

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.

 

You can set the forced open loop idle flag:

Option Word 1 - Bit 2 - OpIdl

RBob.

 

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

 

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.

 

The EBL is not capable of "closed loop" at anything other than 14.7 because it is not capable of using a WB for closed loop operation. The stock NB sensor is only accurate at 14.7 and right around 14.7 - it is not capable of accurate operation at significantly different AFR's.

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

 

Interesting when I have mine programmed for 14.2 throughout the entire VE table as its' base.

Who here said that a WB was capable of CL operation...?

Narrowbands know rich, lean and stoich depending on oxygen content. I myself run an ethanol blend. You trying to tell me that I cannot set my stoich value as anything other than 14.7 in CL is irrelevant to me, because mine is set where I have it set, and it has been so for quite a few years. What's next, you're going to tell me that I cannot change the "128" BLM stoich value to anything other than 128, and that it is hard coded in the firmware lol? Tell you what, you stick to what you think you know and tell yourself, and just ignore my posts the same way I ignore yours...

- Rob

 

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

 

The 749/730 ecm running $59 was suppose to have wideband closed loop. I never tried it tho

 

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.

 

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

 

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

 

No one here on my dyno tunes with closed loop ON. LOL. That would be ridiculous. Literally the LAST thing you do when tuning is turn on and calibrate the closed loop control.

GD

 

I tune in C/L.

 

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

 

So am I correct in saying the AFR table is a reference point for VE learns and doesn't affect fueling until you bring in the VE learn results into a new VE Bin?

 

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???

 

It may be part of the fueling calculation, yes.

Make some changes to it and see what happens on your wideband.

GD

 

Here is the PW calculation in open loop (although the BLM will be used if above 128):

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.

 

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..

 

Remember that closed loop was only invented to enable dual bed 3-way catalysts for control of NOx. The original catalyst for HC and CO didn't need that precise a level of control. When the emission requirements for NOx tightened in MY1981 for US emissions, it became necessary to control to very near stoich so that both catalyst beds work to optimum efficiency. The image below shows catalyst efficiency vs a/f ratio. Lambda of 1 is stoichiometric or ~14.7:1. Before 1981, engines were generally tuned for lean running to keep the catalyst efficiency for HC and Co maximized. It can still be useful to use stoich as a reference point, but in a car without a 3-way cat, there is no technical reason to run in closed loop.

 

dan5, thanks, getting the message....