Closed Loop mode

[MTCFORUM]

Who can tell me more about closed loop mode. I've been reading a book about Chevy ECM systems, and now come up with several questions.

first question.
are there any cars now running in closed loop operation all the time? The book I read said that they only ran in closed loop operation during part-throttle operations (due to sensors only being accurate at or near 14.7:1 air/fuel ratio). Since the book was published, have sensors been developed that work at WOT?

Second question.
As I understand it, during closed loop operation, the ECM takes readings from the O2 sensor. It uses those readings to adjust the fuel mixture. One of the problem stated in my book was that the mixture was adjusted "overall" but no specific adjustments were made for each cylinder.

Would it be possible (or practical) to have long tube headers with 8 02 sensors (one in each tube) measuring the a/f ratio of each cylinder? In the real world, I have trouble believing that all cylinders flow the same volume of air and run at the same ratio. So instead of adjusting all 8 injectors based on one or two 02 sensors, wouldn't it make more sense to adjust each injector based on that cylinder's real a/f ratio (instead of an avreage number)?

Am I way off track on this one? Or is this stuff out there, but just too expensive for production vehicles. I would think that it would make for more power with less emmisions.

Brian

p.s. I now know why chevy's are POS. They converted from MAS to speed density in 89. Not only is my 91TPI speed density, but they used batch fire instead of sequential injection (hmm, what year did ford start using sequential injection)??.

[MTCFORUM]

<i>first question.
are there any cars now running in closed loop operation all the time? The book I read said that they only ran in closed loop operation during part-throttle operations (due to sensors only being accurate at or near 14.7:1 air/fuel ratio). Since the book was published, have sensors been developed that work at WOT?</i>

Fords run closed loop at idle and part throttle after warmed up. I don't see any way to be closed loop at cold start short of every car having wideband sensors, since the normal O2 can't read properly in rich conditions needed to start cold. Little to no improvement to be had too I suspect. So yes a wideband sensor would work at WOT. Some Hondas came with a wideband, I'm working on soldering up a homebuilt wideband unit that uses their sensor.

<i>Second question.
As I understand it, during closed loop operation, the ECM takes readings from the O2 sensor. It uses those readings to adjust the fuel mixture. One of the problem stated in my book was that the mixture was adjusted "overall" but no specific adjustments were made for each cylinder.</i>

This is correct for some cars, for ours and others they have 2 sensors and each bank is adjusted.

<i>Would it be possible (or practical) to have long tube headers with 8 02 sensors (one in each tube) measuring the a/f ratio of each cylinder? In the real world, I have trouble believing that all cylinders flow the same volume of air and run at the same ratio. So instead of adjusting all 8 injectors based on one or two 02 sensors, wouldn't it make more sense to adjust each injector based on that cylinder's real a/f ratio (instead of an avreage number)?</i>

You are correct. It all comes down to cost. This would provide a small amount of additional power/efficiency. Same can be said for individual timing for each cylinder.

<i>Am I way off track on this one? Or is this stuff out there, but just too expensive for production vehicles. I would think that it would make for more power with less emmisions.</i>

It's all due to cost.

[MTCFORUM]

Kris is correct with all he said.

One thing to add is that on newer cars, TLEV or LEV emission levels or lower, even on a cold start as low as 20F, they go closed loop in less than 30 seconds.

Also, the EEC learns the correction it needs to maintain 14.64:1 a/f ratio at various speed and load points. Then the next time you go into that cell, it applies that correction so it should have to correct as far to make the O2 sensors switch.

Also, part throttle is not the best term. Basically you are closed loop until very, very heavy throttle for increased power. this is like 80% or greater throttle in the newer cars.

There were some stupid things done, like with your Mark Brain, where they went open loop at a given vehicle speed because, well, they could. Ever notice a speed that all of sudden your gas mileage goes in the tank?

jerry

[MTCFORUM]

If a wideband sensor was installed for use at WOT, would you have the ability to leave closed loop mode on at throttle above 80% all the way to WOT? I understand the sensor would allow it, but is there parameters in the EEC you can change to make that happen?

Can you control how closed loop operation is managed through adjustable parameters in the EEC?

Jerry, I find that very intresting. How many years did that take place? Do they go back into open loop mode at speeds above where emmisions are tested (like 70+mph)??? Is there any way to correct that besides replacing the EEC with a newer one?

thanks for the info
Brian

[MTCFORUM]

There is no software to run a wideband in the current EEC, you can't do it. All you can do is tweak the air meter transfer function so that you get the A/F ratio you are asking for.

The way to fix the open loop stuff is ONLY with a chip. It was done like that all the way through 1998, although not as aggressively.

It was at speeds like 80+ MPH.

jerry

[MTCFORUM]

Hey Kris,

Did you order a wide band kit from DIY-EFI? I orded the Australian kit. Hasn't come in yet though. It looks like it's pretty easy to assemble if you have some electronic background. I shouldn't have any problem then. How are the instructions, and cal procedures?

Lonnie

[MTCFORUM]

is this the site you are talking about lonnie <A HREF="http://www.diy-efi.org/diy_efi/" TARGET="_blank">http://www.diy-efi.org/diy_efi/</a>
There's a lot of neat stuff there!!

add this site for lots of neat info on the basics of engine managment. members.aol.com/dvandrews/ems.htm

Jerry,
Now that I think about it, I think it's possible that I have seen the side effects of the speed limited closed loop operation. We have taken a couple long trips, and when my girlfriend drives, she usually cruises between 75-80mph. I tend to drive 80-90 in the 70mph zones. I've always gotten significantly lower gas mileage than her when I drive one way. I always thought it was just because the car was much less effecient at 10mph faster, but we're talking the diffrence between 415 miles a tank (girlfriend driving) and about 355 for me(last time).

[MTCFORUM]

I'll tell you what, the EEC adds in like 10% more fuel, roughly, when you get past that point. It's also tied to RPM so if you drive about 3000/3100 rpm it's also open loop all the time.

jerry

[MTCFORUM]

Yes that is the site I'm talking about Brian.

Lonnie

[MTCFORUM]

Lonnie I did order all the Aussie parts but they aren't here yet. I agree it should be rather simple to solder up. Looks like a few people on the EEC tuner list built from those kits and have them working just fine.

[MTCFORUM]

Kris,

Yeah I ordered the the WB kit but nothing has showed up yet. The only parts that they said don’t come with the kit is a heat sink for U7, the heat sink mounting hardware, a 3x14 pin IC so+A54ckets what ever that is but I’ll figure it out and a R40 1w resistor. I also ordered the board itself and Digital AFR display. If I have any problems I won't have to go far for help. Since I have four guys that work for me that build their own robots from scratch and program them. You know like the ones you see on Battle Botts. Then I have about 25 other very talented electronics types that conduct the repairs, maintainance and operate the Deep Ocean Remotely Operated Vehicles and Side Scan Sonars here at work.

Lonnie

[MTCFORUM]

Lonnie sounds like you should be in good shape. The only other thing I think they fail to mention is that they don't include any kind of enclosure for the board. I'll just wait till it gets here, measure it, and go pick up one of those little aluminum boxes at Rad Shack or Fry's I guess.

[MTCFORUM]

Well it is all here. It's a lot more complicated than I thought. Smaller than I thought. I was under the impression that the box housing the LED readout was all assembled, but that is all in kit form too, board has nothing on it, and lots of little parts. I'd say this will be the most complicated board level work I've ever attempted by far.

[MTCFORUM]

sounds like fun!!! Do you have a digital camera to snap some kit pics?

How exactly are you going to interface that with the EEC, or are you only using it to display the a/f ratio at higher rpm's to help you tune?


Brian

[MTCFORUM]

Hey Kris,

Yeah I knew the Digital readout was also a kit. I didn't think it would be any harder to put together though. I got the confirmation of my order but my Pay Pal account still shows no activity. How long before you got any sign things were moving? Oh and did you see on the Tuner board the post about having someone build it for you...lol. I don't plan on mounting mine since I have more than one car to play with. I figure I can come up with some box or even a Pelican case that I can carry to each job. And I'll probably be using it on friend's cars too.

Lonnie

[MTCFORUM]

Brian there's pictures of pretty much everything ont he site already, <A HREF="http://www.techedge.com.au" TARGET="_blank">http://www.techedge.com.au</a>

Lonnie I still think it's going to work out, just more effort than I anticipated. The boards are smaller than I thought, anf the display unit actually has 2 boards of its own. I ordered mine during christmas break, the guy sent me a paypal payment request just after the new year, I paid it right away, and here it is today.

[MTCFORUM]

Anyone get theirs working yet? I plan on ordering one. Just not sure if I should get it as DIY or a completed kit. Pointers anyone?

Thanks, David

[MTCFORUM]

David,

Check out the EECTuner forum over on ezboard. This is where I first heard of it and a lot of those people are building the wide band. Jerry has some good posts there also.

[MTCFORUM]

Okay, I don't want to sound like a retard, but I just spent about 1/2 hour looking for this place and I CAN'T find it. Where exactly is the "EECTuner Forum"?

[MTCFORUM]

My bad. Check this out:

Check out <A HREF="http://www.iwantperformance.net/cgi-bin/ultimatebb.cgi" TARGET="_blank">http://www.iwantperformance.net/cgi-bin/ultimatebb.cgi</A> for lots more info.....


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<BR><BR>
[Modified by pwilbur, 11:05 PM 3/5/2002]

[MTCFORUM]

I also have the Aussie kit and Jaycar display. I have the display done, it was much easier to build than the WB board. Note, the mods required for the display board to work with the WB are not documented very good IMO.

If you don't have one, I highly recommend picking up a grounded, fine tip soldering iron. Radio Shaft has them for @ $15. The transister pins are mounted extrememly close together, you'll need a fine tip to avoid bridging the connections.

If anyone has any heatsink ideas let me know...I really don't want to use a huge AL plate like they suggest, I'm tossing around the idea of a 'finned' TO-220 heatsink and a small 12V cooling fan.