11sORbust

I know that some people run open loop all the time. IMO, there is no reason to run open loop IF you don't have to. My engine is a 406,cam specs 242/250*_114lsa_.570" lift. Right now I can say that it's tuned fairly well. My IAC controls the idle perfect. The blms work fine. Why would I "need" to run open loop? I love closed loop. The ecm controling stuff is fine if you know what's going on.

This is not a thread to slam open loop users. In fact I would love to hear the reasons to run that way. Even if I still don't agree then at least I'll understand. Maybe I will be forced to use open loop if I keep modifying my engine. I don't see that happening because I already have a good handle on my tune and it's just about finished getting built....

Grumpy

If you car runs fine, closed loop, so be it. Remember it's just about giving the engine what it wants.

But, unless you try open loop, you have no valid comparison. Your just kinda guessing your engine is HAPPIEST there.

Some engines run fine at 14.7, and some run fine leaner then that and some like richer then that.

Using closed loop can be great for getting things close, and have the PE AFR jive with what you think the engine'll like.

I woundn't suggest for anyone less then the well experienced to tune in just open loop without a WB. Without a WB it takes alot of work to get close.

11sORbust

I agree with the first part. The second I would have to say that my engine is getting 20+mpg, runs smooth and cold start is great. So I really think that tells me the tune is good. I have ran other cars on open loop. It's not that bad IF everything is really close. But things like seasonal weather changes will effect what you input. That is one reason I like closed loop.

RBob

iTrader: (1)

Ahhh, then there are calibration problems. If seasonal changes affect the end AFR/SA/tune, then there is something else in the calibration that is incorrect.

I've found that even running closed loop it is important to get the calibration correct. Otherwise the fueling changes too rapidly for the INT/BLM to keep up and the driveability suffers.

RBob.

11sORbust

Not sure what you mean. If I tune my ve tables when it's 20*F then the a/f ratio will be correct when it's 95* in a few months(in open loop)?

Let me run this by you guys. We'll say that you are in open loop all the time and got the ecm to read 14.7 under all part throttle conditions. Now we test how well the ecm keeps a steady 14.7. My idea is to use idle as example. Let's say that you just came off the highway and hit a stop light. The wb is holding 14.7 at idle. NOw go through bumper to bumper traffic. I would bet that a/f will start to drift under that condition. The only way to avoid a/f drift is to use BLM. What do you think?

Grumpy

I can break 30 MPG, but I also lose 5 PSI of oil pressure. The Lean Cruise is right at an AFR of 15.2, but takes 46d ignition timing. The extra timing puts alot of heat in the oil. So while it performs well there, the down side is oil degragation, and bearing wear. I don't consider that as the motor being happy.

11sORbust

I have never had the desire to used highway mode or lean cruise....


I'm suprised that nobody has said they use open loop all the time. It would be great to hear why they did that.

onebinky

iTrader: (1)

11sorbust, is your car map or maf?

In open loop, the only sensor the car isn't reading is the o2, correct?

(not trying to make a point with those questions, just trying to understand better )

What would be the main benefit of running open loop all the time? Wouldn't you loose efficiency because the ecm has to reference the default tables? Or does that tie back into the low resolution of the switching type o2 sensor, and us having the ability to tune exact with the WB o2?

But then still, how does the computer compensate for atmospheric and temperature changes if it can't see how much fuel it's burning?

Thanks guys, I tried doing a search on the open loop tuning a little while back, but didn't turn up to much.

onebinky

iTrader: (1)

Also, I don't recall the MAF cars having any kind of a baro sensor. How do they compensate for air density changes anyways? Is that through the MAF also?

Do the MAP cars have a baro sensor integrated into the map sensor?

Thanks again

11sORbust

MAF sensor compensates for baro...so does MAP. From what I understand.....

I have map/730

RBob

iTrader: (1)

IAT/MAT sensor.

RBob.

11sORbust

so you are 100% sure the a/f will not "drift" from what's in the tables, under all conditions?

RBob

iTrader: (1)

My stock '92 does that now. At idle the O2 sensor cools off and the AFR drifts, then as the O2 continues to cool off the ECM goes open loop. On cool wet days the O2 sensor reports lean and the AFR goes rich. Finally melted the cat. Factory stock f-body. . .

RBob.

11sORbust

That doesn't sound right to me. Did you have an exhaust leak or something? My car does not do that...if that was normal then GM would have alot of burned cats to recall..yes? FYI, I don't run any emissions equipment...

So you going to run it in open loop all the time? If so the could you explain why someone would want to. I know things like racing or cam lda would be better off in OL. I was under the impression guys here ran that way all the time

RBob

iTrader: (1)

The day it took out the cat was a 2 hour drive on a limited access highway. So it kept building heat with out a break. I am also going to put a heated O2 in it. Anymore I don't drive it unless the weather is nice. It is still a closed loop system with a cat.

Back to the open loop, how well it holds AFR depends upon how well the calibration is done. An ECM such as the '8746 has limited intake temperature compensation. But then again the entire manifold under the TB and runners is a water jacket, and the aircleaner has a thermo-vacuum switch for intake air temperature control.

Change that to open open element air cleaner and the AFR moves all over the place.

With my hot-rod I run open loop except at idle. The closed loop idle helps a lot due to the short injector PW (TBI @ 0.9 to 1.0 msec PW). That short of a PW requires some feedback to keep the idle fueling under control.

This system also runs an IAT sensor behind the front grill, has a cold air induction system to the base of the windshield, and a limited amount of coolant through the intake manifold crossover (where the exhaust is normally run under the carb pad).

By using a combination of IAT and CTS the AFR control is pretty darn good. It took some time getting the IAT/CTS combo right, mainly due to needing different ambient temperatures, but it's good now.

Some masks run a in-idle fudge factor to compensate for heat buildup in the intake manifold. When the ECM recognizes that the engine has entered an idle state, the code slowly adds heat to an IAT term.

RBob.

Grumpy

It kinda depends.....

If the code your running allows for the accuracy, and the mechanical bits are right, then it should.

If you look at the air in the plenum, and whats going past the intake valve, then you can get it right. In a code that allows for accurate MAT profiling for timing and fuel. And toss in a lil for coolant temp..

Gets more and more interesting the deeper you dig.

JPrevost

From what I've gathered over the years, closed loop is an emissions thing and a backup system. On an engine with a "perfect" tune, running closed loop would sacrifice a lot.
The compensation tables for IAT, CTS, AE etc. are there because closed loop with a narrow band o2 is an inaccurate system. 14.7 isn't the AFR for when you're loading up the engine but aren't using enough TPS to go into PE mode. This is what I've FELT running both systems. In open loop I'm able to manipulate the AFR depending on the engines condition. If the engine is loaded and low engine speeds, 14.7 isn't going to make the engine as "happy" as a lower AFR.
Besides, closed loop in stock calibrations don't hold the engine at 14.7! It swings rich to lean to keep the cat happy.
About the cats failing, from what I've heard, GM actually runs stock calibrations with a LOT of fuel and not a lot of timing to put OUT the cat so as not to overheat the element.
With this being said I think closed loop is great for mild engines with emissions and a cat. Anything else and closed loop should be used to get the VE and compensation tables close, then run open loop with a wideband and you're set.
I think the closed loop is also a good way of keeping an engine running if a sensor fails while you're driving. I recall the 8746 tune has default values to assume when a sensor fails but the o2 sensor is the safety net... or isn't it?

Grumpy

:lala:



And but of course in Off Road Use applications

11sORbust

I'm trying to figure out how to change a/f ratio in closed loop...... So why is open loop better, aside from a/f issue? If my tps goes out my car has a better chance at running half way decent. What about a fuel delivery issue. Maybe your f/p regulator starts to malf. So instead of blm drift, the open loop user will have a/f ratio drift. HOw often do you check f/p(while driving), it could be awhle before you catch that one. Or you are sitting in traffic on a very hot day and the intake heat soaks big time. Same thing, yes? IAT/MAT malfunction.....ouch!

Guess my point is why should I disable closed loop if I can command the a/f ratio? I don't think it's "holding back" my idle/part throttle. The gas mileage is fine. If part throttle was any more responsive it would snap a neck. Things are not perfect by any means though.

I can say that it ran great at the track. There was maybe 45min wait to stage. The engine was on the whole time. Coolant temp never budged...not even when I ran.

I like having that safety net . My car is getting built to drive. Maybe take it on some long trips. Plan on logging over 100,000 miles on it. It just seems like closed loop is great if you can contol it.

11sORbust

I can only think of two reasons that people stop responding.

1. Because I sound like a moron.
OR
2. nobody can answer the question(s)

???

I can put $10 premium,drive to the track(30 miles) and run the **** out of my car, then come home on the same amount of gas. This is all in closed loop. Fat cam+ closed loop=no problems .So why should I disable it? I'm very open to discussions...

proryder2

11s or bust i have been reading alot of forums latly and all the stickies i could find but still i can`t find an answer to this. does a big cam throw off the o2 sensor. i have a 406 like you with a big cam and im planning on converting to tpi but i wanna understand tuning a lot more before i do. so to kinda jump off the subject. what compression ratio are you running?

RBob

iTrader: (1)

To define your question, from the first post of this thread: "Why would I "need" to run open loop? I love closed loop."

I believe that I showed there is no "need" to run open loop. I have one car I run closed loop idle and open loop off-idle, and why I do that. Another vehicle I talked about is factory stock and is run as the factory intended. Another vehicle I retro'd TBI onto (with a stock '85 LG4 engine), I run closed loop, and with a cat-con (hint).

Not only all this, but the GM RamJet engine package with the MEFI controller is an open loop system. Yes, it can be changed to closed loop, but it comes from GM as open loop, no O2 sensor. (I do believe that the newer ones may now come closed loop, w/the MEFI3 controller)

And they have sold boat-loads of these packages (engine/harness/ECM).

So, to answer your question: "There is no need to run open loop." And unless there are cat-con's involved, there is no need to run closed loop. It's just that in some instances open loop works better. Try it, can always change that one byte back if you don't like it. . .

RBob.

11sORbust

I'm running 10.1 CR .With the big cam I'll need to bump it up to 12.1 . With a low CR(for cam) the idle and low speed stuff suffers.. Once I get it up to 12.1 the idle will be smoother. Not a big problem, just most people slap in a fat cam w/o increasing CR. That will kill track times too...

BUT that's not an issue, it'll be fixed soon.Right now I have tuned it very well and the throttle response is great. I'm even breaking free the tires at 80mph on upshift(at the track)

11sORbust

I guess that covers it. Not sure of the instances that open loop runs better though. BUT that response will work....

Thanks for the replies.