I would have to say that open loop is best. I can't ome up with one reason a car would run better in closed loop. Of course tuning in open loop is easier, you are not fighting the ecm correction. IMO, the correct way to tune is in open loop, then switch to closed and see how it does. If your o2 and calibration is good there should be no difference between open/closed, on a stock setup especially . The only difference I see is the crazy a/f dance

 

Actually there can be a big difference between how the engine runs in open loop vs. closed loop. In closed loop the feedback tries to maintain an AFR of 14.7:1, or close to that.

In open loop the AFR can be varied across the spectrum. At low loads it is typically high, as the load increases the commanded AFR decreases.

This makes for an engine that is more responsive, smoother running, and less detonation prone.

RBob.

 

That's why I'm thinking about going open loop. all the time...

 

So... who's going to write the "Open Loop Tuning" article and sticky it?

 

This is the best response I have seen and an extremely true statement:-). You will need to do it yourself to experience it.... Truly a major difference.
later
Jeremy
PS will an open loop tune do better with blowby pushing the dipstick out? ill find out lol

 

Now this seems (to me) to be a much better reason/goal to run open loop than the observation "closed loop AFRs swing around too much". Very nicely put! :hail:

 

I dunno.
Closed loop can be a huge aid in which way to go and how far. For the new guy with that's planned ahead and is working to learn tuning, closed loop, IMO, is the only way to go. Now, for someone that's dove in, with a hotrod engine, and is starting at square one, open loop is definetly they way to go, at least initially. For the guy that's been at it for a while then it just blurs into what makes the engine, the Happiest.

So far, it seems to me that I spend about X amount of time to get a particular engine tuned correctly. MAF or MAP, Closed or Open Loop, it all takes alot of time to get it right, from what I've experienced. There just aren't any shortcuts, it just takes time, and to a certain degree experimentation.

FWIW's,
The truck just doesn't care, as far a drivibility. Thou, in closed loop with corn gas it did get it's best mileage ever, 11.1 MPG towing with the GN on the trailer, with the A/C has been it's best yet, and that was with a *high* timing chip. High in the case being the advance limit set to 36d.

The GN with the stock ecm and code, MAF, in closed loop, was always slightly lame, compared to what could be had in open loop. The GN with the ROmless conversion, and MAP, well that was Open Loop only, and it's just the standard by which I judge all others so far.

With the stock 58 code Open or closed loop there was little difference, in tuning time or drivibility. While doing the 58 code thing, I spent alot of time in both Closed Loop and Open loop playing with BPCs, etc.

Probably a combination of both would be ideal. Using a WB and feedback for AFRs other then Stoich would be a fun thing to try. As well as MAP other then PE, and then MAF for PE. MAF in this case being the late model high freguency ones, with enough table resolution to really get it correct. Or possible a learn feature for a range of AFRs while in PE. But, IMO, that sort is living dangerously unless the code is done correctly. The new OBDII stuff sounds more and more interesting in that reguard.

 

Sorry, I'm not Mr articulate
























Just kidding!

 

Got a driver for 3 hrs or so t'row nite(my gf for those who know)

So hopefully I can work out a large portion of the VE table in open loop and see how it fairs. Initial testing was very impressionable.

hoping to not have a terrific nitemare and using my currently running bin as it is fairly close to the 128ish area for my engine.

If i get another chance I also have made a setup base bin for running open loop as well.
later
Jeremy

 

If you have a tune with the VE table worked out in closed loop, it will work in open loop. In open loop the commanded AFR will be different from 14.7:1. This is where the beauty of open loop lay.

In the $8D mask there are two open loop AFR percentage change tables. One for coolent and the other for load (MAP). If I am correct these table adjust the commanded AFR by a percentage from the base stoich term.

Set the closed loop enable temperature to 151 C and drive it. The data log will show the commanded AFR. I'll bet the stock open loop AFR tables will be close enough that the engine will run nicely.

Only change the VE table to match the commanded AFR to the WB AFR.

RBob.

 

14.6-14.7 from off idle to 2400-2500 or so worked real nice with the idle afr at 16-1 on the wideband. After that uner any type of load(70kpa up) it seemed much happier and smoother pulling with a slightly richer, say low 14'2 or so as u progressed and kept going into PE..
This range is a real trouble spot for me and I always get knock there unless I force it richer. My midrange has always lacked and the timing moving up and down never helped but going richer always did. Might just flat out want more there were the cam comes into its own and the tuned freq. of the runner design.

As long as my neg battery term. (dont ask) doesnt fall out this time I should have some more answers

later
Jeremy

 

So the VE tables also effect Open Loop?

 

YES!

All the fueling is based on them (other then if the processor dies).

 

quote:
--------------------------------------------------------------------------------
Originally posted by RBob
Actually there can be a big difference between how the engine runs in open loop vs. closed loop. In closed loop the feedback tries to maintain an AFR of 14.7:1, or close to that.

In open loop the AFR can be varied across the spectrum. At low loads it is typically high, as the load increases the commanded AFR decreases.

This makes for an engine that is more responsive, smoother running, and less detonation prone.

RBob.
--------------------------------------------------------------------------------


What if you use a WB while in open loop and tune the VE table to match 14.7 on the WB. Wouldn't this get your closed loop operation pretty darned close in closed loop?

Forgive my newbie question, I'm still learning this stuff and only have a WB "in the mail", not in-hand yet...

- Ye Old Phat Phart, Vern

 

Only if the commanded AFR is 14.7:1 throughout the range. In open loop the commanded AFR will vary, unless the bin has been changed to be 14.7:1 throughout. I've never seen a stock GM bin like that.

RBob.

 

I disagree with the comments that 14.7 is only to keep
the cats happy.
When there is a lean/rich O2 sensor flip,
the engine 'knows' that it is near stoick,
when the engine 'wants' to go to another
air-fuel ratio, it uses the 'lean-rich flips'
as known points, and calculates from there
what it needs to do.

 

Can you document why you disagree?. With quotes, from knowledgeble sources?.

In everything I've read from the early day of DIY-EFI when there were factory engineers on board to patents in reference to cats, they mandate 14.7, and running rich and lean to supply the energy to pump the reactions.

When you producing millions of cars a year, the oems get real retentive about warrranty claims, when they can cost over $100 per car. And in the case of one Caddy incident it was $400 a car for the cat warranties, from a mistake in processor coding, that FUBAR'd the AFR swings, under certain conditons.

 

Do you have a technical basis for your conclusion?
And yes 14.7 is where the cat will survive longest. Richer/leaner than 14.7 will cause damage, over long periods of time, just ask the local exhaust shop..

Rbob burned up a cat just sitting in traffic, going into open loop, from what I understand...

 

14.7 *is* the operating point the cats need to operate. Including a relatively small AFR swing to supply excess oxygen and CO. There is a *lot* of information available that goes into any level of detail you'd like to confirm this.

Have to put some constraints on this. In general, cats will "fail" from either getting contaminated (i.e. burning oil) or getting too hot. Unless you're dumping a *lot* of fuel into the exhaust from an excessively rich mixture (or misfire) and/or going extremely lean thus heating things up, smaller AFR deviations won't hurt the cats. (There are other things like excessively retarded spark that can heat things up, too.) They won't "work" during these smaller deviations. But, they won't be "broken" by them either. Going back to stoich will bring things back in order.

 

If you are referring to me, the cat I had burn up was on a bone stock '92 Camaro. No ECM mods, no engine mods, just the way it came from the factory. Long highway drive (2.5 hrs) at a good rate of MPH, overheated the cat and burned out the mat surrounding the brick.

Rattled like crazy, so it got replaced.

I believe the actual cause is because of the O2 sensor location. It is located in the Y pipe after the Y. On this particular day it was cold and wet out. A light misty rain and around 38 f. On days such as this I've noticed the gas milage decreases dramatically. I figured that the O2 was cooling off, dropping the reading, with the ECM compensating with more fuel.

The additional fuel was enough to overheat the cat.

RBob.

 

I was under the impression that 14.7 AFR was more for the emmision requirements than anything, but I will accept it for the design of the cat.

So what if you don't have a cat conv? IE it is gutted or completely removed? Would open-loop driving benefit your tune even more?

Also what would be the effect of gas milage running in open-loop all the time? Just from reading above on the rich-lean swing of things with NB sensor trying to keep that magic 14.7 number.

 

A) Would depend if your set up liked some other then 14.7.

B) Would depend if your set up liked some other then 14.7.



Running lean means having to add more advance. I've gotten about the same mileage at 13.2:1, as at ~16:1. The 13.2 was alot easier on the engine.

 

I have been struggling with an ultra lean engine 17.0:1AFR in closed loop at idle and cruise. I found this post as a result of a recommendation from another post. I raise the closed loop temp to 255*f and gave it a try. After resetting the memory everything came back into check. The idle and cruise AFR are now high 13's to low14's. The idle is smoother and more importantly the heat build up is way down. I'll admit that I probably have much more tuning to do but I'm impressed with how the car runs much better. This leads me to seriously question the factory setting for stoich especially on a modified car. I tried to adjust all of the tables for 02 that are in TunerPro but none of them did anything. Now this may be because (unknowingly) I wasn't reseting the ECM every time. I was pulling the ECM fuse instead of the red wire near the battery. I didn't find out until after I made the open loop change that the fuse wasn't dumping the memory. My bad! I will have to look further into that issue but I am very happy that the open loop trick has pointed me in the right direction i.e. 14.0:1 AFR's!!!
Thanks to all for your help!!!

 

To reset the ECM all you have to do is pull the NEGATIVE (black) wire from the battery for 5-10 minutes. It's much safer than pulling the positive (red) cable and just as effective.

Take this from a person who got zapped really bad by a car battery 2 years ago - knocked me on my butt, welded my metal watch band shut (what touched the + terminal and grounded on the radiator mount), caused 2 third degree burns on my wrist (one a each contact point) and ate away about 3/16th inch meat from my wrist at each spot, and left me disoriented and kind of goofy for the rest of the day. Never mind that some folks say I'm still that way....

You NEVER want to mess with that positive cable while the ground cable is still connected!

Hope this helps and maybe saves someone a nasty burn --- or worse.


- Vern

 

You know, ive been thinking. My '8746 ecu wont really be in o/l @ WOT above 4000 rpms. Im now running o/l all the time now. My ecu was trimming. My PE only goes to 4000 rpms. Unless i dont have that part of the map tweaked high enuff to throw it into o/l (hi 02 to stay c/l = 850mv). I did move up the VE adder to achieve 100% VE 4000 rpms and over. I always "asumed" it went into o/l @ WOT till now.