West Coast GTA Man

Hey guys I know this is probably an easy question and you may think a stupid question, but what exactly is closed loop, and how do I know if my car is going in to closed loop?? I know it has something to do with temp. My car is running great, but I was just wondering, because I changed to a 170 thermostat, and put in a cooler fan switch, and I wanted to make sure that everything is correct and I am not having any problems that I am not aware of. I have seen a few questions about this, and wanted to know.
Thanks alot
Mike

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Gran Turismo Americano "The Ultimate Firebird"
Smokin 1989 GTA- Bone stock except for exhaust. (no catalytic-stainless pipe into Flowmaster 2 chamber) & AC Delco Rapid Fire Plugs

RB83L69

Think of the entire control system on the car as a "feedabck loop"... the ECM commands a change in something, the change occurs, the ECM can see and measure the effect of the change; then it can command another adjustment, the change occurs, the ECM can measure the effect, etc. until the controlled parameter whatever it is reaches the value or condition that the ECM desires it to be in according to its programming.

"Open loop" does not use feedback. The ECM commands the various controlled devices according to a fixed set of values in a lookup table, but does not check to see if the results are affected. Furthermore, in the case of the ECMs in our cars, if the ECM finds that it consistently has to adjust its commands to some different value from the "nominal" ones in order to bring the controlled parameter back into spec, it can alter the values in its programming. So fo instance if it's expecting to see a specific O2 sensor indication, in "closed loop" it selects a duty cycle for the injectors based on throttle position, engine vacuum, coolant temp, etc. etc.; produces pulses of that duty cycle; then checks to see if in fact the O2 sensor reading went to where it expected; and if not, adjusts the pulse width slightly, checks again; and keeps doing this until it's satisfied. If it finds every time it sees those same conditions that it has to for example shorten the pulse width by approximately the same amount, it puts a "learn" value in that particular cell in its table that tells it to adjust the pulse width by that amount every time it sees those conditions. In this way, the car can actually "learn" the habits of the driver, the climate, the altitude, the kind of fuel it's being fed, etc.; and it can attempt to complensate for changes in any of those external variables that affects it.

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"So many Mustangs, so little time..."
ICON Motorsports

ATOMonkey

That's not entirely correct, in fact it's backwards. Open loop is generally used by the vehicle or user to adjust control system gains and initial values to make the system respond differently. That is the learning algorithm that was referred to. Closed loop uses only pre-set values in tables and proportional and intergal gains for transient response. The gains are what determines how fast the engine and transmission respond to throttle position and engine/trans feedback. Closed loop normally occurs at wide open throttle, or when a sensor fails or is out of spec. Closed loop control also uses engine data as feedback for the control system, but does not adjust the gains or initial settings. At wide open throttle, fuel delivery is simply a function of RPM. That is why you can change running conditions at WOT with fuel pressure adjustment. That is why sometimes cars run better in closed loop. If a sensor fails it will go to a default value and not respond to the rest of the system. This usually results in poor performance. In the case of Ford, the default values were for high performance instead of limp home mode, so to get the early EFI Mustangs to run better you discontect all of the sensors(tricky bastards). All Closed Loop really means is that the engine is running on its own without user or vehicle intervention.

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[This message has been edited by ATOMonkey (edited August 09, 2001).]

8Mike9

Say what?

8Mike9

In simplistic terms, closed loop mean the ECM now is trying to tune the engine for the best fuel and emissions it can achieve, basedon preset parameters in the EPROM.

All sensors are monitored and utilized in feedback to the ECM, ECM reads the sensors and make appropriate adjustments to fuel and timing.

PE (power enrichment) mode is utilized at WOT, the ECM is techinally (I think) in Closed loop, but makes no adjustments for fuel and spark control based off of sensor input.

I/e in normal closed loop mode the ECM is trying to maintain an AF ratio for milage and emissions purposes, in PE mode, this info is bypassed and the engine gets what is programmed in the EPROM for this mode...it could care less if you're running rich or not, there is still some feed back monitored and adjusted..i/e the knock sensor, ECM will retard timing of it get's knocks in PE mode.

ATOMonkey

I know I didn't word my response very well, but I agree with everything you said except this.
Other than that you hit it right on the head.

Brent

iTrader: (1)

ATOmonkey: You've gottem backwards.

Closed loop - the ECM uses the O2 sensor to correct fueling.

Open loop - the ECM uses the preprogrammed tables for fueling. No feedback is possible because the O2 is to cold to report correctly.

ATOMonkey

OK I'm not trying to get into a pissing match with anyone. I guess that our terminology is not meshing. All the control systems that I've worked on have used Open loop control as a way to calibrate and troubleshoot the engine. That didn't mean that the engine wasn't operating normally(even when warm) it just meant that the calibrator had control over the electronics. Closed Loop control was used for parameters that were proprietary for the software company that designed the system, or when the engine was not connected to a development tool(even when cold). I guess I should have known what I was talking about a little more before I open my mouth.

Jason Welch

Jason Welch

Sorry about that new to this. Just wanted to highlight "How do you know when your car is in open loop"

Grim Reaper

There is actually more to all this, but I don't want to confuse people more than they already are. There is Closed Loop vs Open Loop and there is Learn Mode vs Non-Learn.

Generally Learn only occurs at Closed Loop. As mentioned by others, Closed Loop uses the O2 sensor to make modifications to the fuel trim to ensure you are "stoichemetric" at 14.7:1.

Open Loop, there are no corrections to the fuel trim based on the O2 Sensor readings. The ECM uses strictly the tables and constants defined in the PROM and based on other sensor inputs EXCEPT the O2 sensor. If the car is in fact a little rich or a little lean, in Open Loop there will be no correction for this as there would in Closed Loop.

As for "Learn Mode", it is actually very simplistic and people should not rely on it for the ECM to compensate. Basically, it uses the last value based on a particular load and rpm level. To update the BLM, it requires a change of at least 2 from the last reading at a particular RPM/Load. If the difference is more than 2, then it is updated in the BLM. It really just shows how much the ECM is having to adjust the injector pulse width from the basic tables. The starting BLM makes the ECM get to a proper mixture quicker and only works at part throttle. WOT does nothing.

It is the BLM (and Integrator) values that guys that burn their own proms use to figure out how much to adjust the tables.

There is also a "Learn" for the IAC. Learning has requirement of a minimum and maximum Coolant Temperature. People that install a colder T-stat effectively cause the Learn Mode to never work. And even eproms that are supposedly designed to work with a colder T-stat, seldom adjust these constants.

West Coast GTA Man

Thanks for the info everyone! I am a little lost. That Sh** is technical man!! I thought I was going to get a simple answer. LOL But how do I know if everything on my car is working properly (Closed loop, or open)? The car is running fine, and I have no problems at all. She idles fine,has plenty of power etc, so am I safe to say that everthing is working ok?
Thanks
Mike

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Check out My Car Pics http://albums.photo.epson.com/j/Albu...667&a=13599419

Gran Turismo Americano "The Ultimate Firebird"
Smokin 1989 GTA- Bone stock except for exhaust. (no catalytic-stainless pipe into Flowmaster 2 chamber) & AC Delco Rapid Fire Plugs

Grim Reaper

Then it's probably fine.

If you want to see what's happening with the ECM, you need a scan tool. Do a search on "scan too", "Diacom", "Ease", and "Auto X-ray". You'll find more infomration about scan tools (and probably their cost) than you ever cared to know.

If you are DIY inclined, Craig Moates has some freeware scan toll that works quite well with MAF. It should also work with SD, but none of the SD guys are using it. Most of us have Diacom.

Yarnboy

Freeware scan tool? I am very interested in this..What do I need to do?

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• Red '88 IROC 305 TPI T-5 w/3.08
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I am looking to buy Edelbrock T.E.S. headers with the y-pipe. I am also looking for a 3.42 - 3.55 posi disc rear. cheesy@fred.net is my e-mail, send a letter if you can help!

Grim Reaper

Go to DIY PROM Board and do a search on "Craig Moates"...you'll find plenty of links to it and where to download it from.

West Coast GTA Man

Hey guys thanks for the help. This group is great.
Later
Mike

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Check out My Car Pics http://albums.photo.epson.com/j/Albu...667&a=13599419

Gran Turismo Americano "The Ultimate Firebird"
Smokin 1989 GTA- Bone stock except for exhaust. (no catalytic-stainless pipe into Flowmaster 2 chamber) & AC Delco Rapid Fire Plugs