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Old 09-25-2013, 12:15 AM   #1 (permalink)
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The FINAL word on DFCO (sorta)

A while back I started this post looking for saturn specific parameters for dfco..
http://ecomodder.com/forum/showthrea...ers-26812.html

Turns out exact answers are non existant because the variables are so stinkin' high. I talked to an executive in advanced engine developement (from one of the domestic auto makers) about DFCO. I was probing for some more answers but left with more information but no actual answers. He said that there are thousands of lines of programming for DFCO alone in the cars ecu.

I struck out on my own to find some answers. I borrowed a listening device and hooked it to one of my fuel injectors. This thing is cool. It has long leads with clips on one end that plug into a small box in the car that also has headphones to listen with. It is often used to find a bad wheel bearing for example. You clip one lead near each wheel and can flip back and forth and listen for the offending item. I clicked it on a fuel injector so I could hear when it was pulsing (clicking) and when it was silent (not squirting the liquid gold we are all trying to conserve).

At first my ears were getting sore from the cheap heavy head phones until I discovered they had enough volume to hang from my rearview mirror and hear the clicking or lack of. I ran around for about the last ten days or so (which is three fill-ups, I drive a lot) with this thing cllicking away. Listening to the fuel injectors alone will get your foot out of the throttle. Learning the DFCO of my saturn was my main goal and I learned a lot but nothing super concrete. Here is the basics for my car. Yours will have its own parameters of course but you will get the idea.

It seemed to drop out of dfco at about 32 mph regardless of rpm
It dropped out in the 1500-1300 rpm range (a few times 1600 or 1200-ish)
If I backed off the throttle slowly it would not go into dfco (or not for a long time)
If I jumped off the throttle (fast tps closed reading) it jumped into dfco right away
If I wasn't fast enough on the closed throttle it would take 2-3 seconds (sometimes longer) before going into dfco.
If i got off the throttle quick enough and was in dfco but touched the throttle (even slightly for a second) it came out of dfco and would not go back in.
In 5th gear it would drop out from low rpm (usually about 1400-1500 rpm).
In 4th gear it would drop out from low vehicle speed (under about 32mph).
In 3rd gear it would drop out from low speed as well.

It was satisfying to be driving along at 55mph and jump off the gas and hear the annoying high speed ticking on my mirror go silent. I knew for certain that as I coasted down quietly that my fuel injectors were not shooting any gas. Another method for seeing this in action (aside from the listening tool or expensive instrumentation) would be to put a little led inline with one of your fuel injectors and watch the light blink or go off.

Another thought on DFCO that I have not read here is you go a little further than you think. I have heard mention about all that compression slowing you down. It is but not quite as much as you think. For compression to happen in the first place you need air to compress. With the throttle plate closed, very little air is entering the cylinder on each intake stroke. I absolutly know the value of EOC as referenced in my above mentioned post. I have avoided it on this car because the fuel pump is marginal and will leave me stranded someday I suppose if I don't replace it. I have driven over 3000 miles in the month I've had it and not been stranded yet however.

Last note (sorry this post is so long),
I now can easily feel when my fuel injectors kick back on if I have been in dfco.
I can not feel when dfco kicks in because it is usually exactly when my foot comes off the accelerator so car is slowing down anyway. Interestingly, while listening to my injectors, they kick back in (start clicking) a second or two before I "feel" the difference in the car.

I hope this helps someone.

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Old 09-25-2013, 07:34 AM   #2 (permalink)
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Very interesting!

The first thing that I learned with my Ultragauge was that my car never entered DFCO. Except, I was wrong. In http://ecomodder.com/forum/showthrea...tml#post391443, California98Civic told me how to detect lean burn using my Ultragauge. I did not find the information in the manual, but I did see that you need to tell it to detect DFCO, and I just realized that in http://ecomodder.com/forum/showthrea...tml#post372073, SentraSE-R told me four months earlier. It is on page thirty-seven in the Ultragauge manual.

Please forgive me if you see me updating other threads with this information.

DaveLobi, this is some very cool research that you did. I never would have thought of listening to the fuel injectors! Thanks for sharing this with us!
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Old 09-25-2013, 08:03 AM   #3 (permalink)
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CRX - '91 Honda CRX HF
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the ugly one - '97 saturn SL just sl,not sl1 or 2
Team Saturn
90 day: 44.15 mpg (US)

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for automatic transmissions..

I forgot to mention that I played with the listening device the other day also on my sons college special car..
1994 Toyota Corolla with an automatic trans and 251k miles. Didn't have much time in the car but found that it easily went into dfco with foot off gas. When we lost enough rpm to lose dfco I got it to kick back in right away by turnig the overdrive off (factory shift selector mounted switch) thus bringing rpm back up into range for dfco. When it dropped off once again, I downshifted into 2nd and it went back into dfco yet again.
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Old 09-25-2013, 09:34 AM   #4 (permalink)
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Maybe I'm buying simpler cars ...

They go into DFCO if you let go off the gas, and start feeding again if rpm drops too low, a bit above idle, i.e. the engine idle control is taking over and will keep the car running @ idle engine speed.
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Old 09-25-2013, 09:49 AM   #5 (permalink)
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CRX - '91 Honda CRX HF
Last 3: 63.1 mpg (US)

the ugly one - '97 saturn SL just sl,not sl1 or 2
Team Saturn
90 day: 44.15 mpg (US)

Vibe - '07 Pontiac Vibe
Team Pontiac
90 day: 44.24 mpg (US)

Hoopdie - '05 Toyota Corolla CE
90 day: 42.58 mpg (US)
Thanks: 5
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Quote:
Originally Posted by euromodder View Post
Maybe I'm buying simpler cars ...
ha, I didn't think there were any cars simpler than a saturn sl (well, at least any that have obd2 at least).

Remember that the idle rpm will be held higher if vehicle speed is up. Mine idles around 1100rpm until just before coming to a stop then finally drops to around 7-800rpm. I would like to have it drop to its lowest rpm anytime clutch is in but that would likely involve re-programing an ecu. Anyone ever beat this high idle at higher vehicle speed?
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Old 09-25-2013, 10:09 AM   #6 (permalink)
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I'll have a look when coasting from higher speeds, but I haven't noticed anything like it so far.
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Old 09-28-2013, 04:26 PM   #7 (permalink)
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Thanks for posting your results. I noticed you mentioned abruptly closing the throttle activated DFCO more quickly. That could be part of the reason why I have so much trouble getting DFCO to activate in my Saturn. I'm pretty smooth with the throttle transitions. Plus, it seems to take 2000RPM+ to get DFCO to activate, anyway. And I rarely rev the engine past 2500. So, yeah...

I wish we had access to the computer programming, so we could tweak stuff like that.
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Old 09-28-2013, 04:41 PM   #8 (permalink)
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CRX - '91 Honda CRX HF
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the ugly one - '97 saturn SL just sl,not sl1 or 2
Team Saturn
90 day: 44.15 mpg (US)

Vibe - '07 Pontiac Vibe
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Quote:
Originally Posted by Blacktree View Post
Thanks for posting your results. I noticed you mentioned abruptly closing the throttle activated DFCO more quickly. That could be part of the reason why I have so much trouble getting DFCO to activate in my Saturn. I'm pretty smooth with the throttle transitions. Plus, it seems to take 2000RPM+ to get DFCO to activate, anyway. And I rarely rev the engine past 2500. So, yeah...

I wish we had access to the computer programming, so we could tweak stuff like that.
Ya, funny that snap closing of the throttle plate (or tps) seemed to activate the dfco immediatly where a ease up on the throttle (as we are used to doing) made the computer think for a little while before deciding to activate dfco. Even more intriguing to me was if I was in dfco and I touched the throttle for even a brief second. The dfco would cut out and not come back on. The computer must be thinking something like "this guy may be ready to accelerate quickly" or maybe "doesn't know if he wants to accelerate or decelerate, better leave injectors on and ready". I don't know.

It would be fun to be able to mess around with our cars computers and play with things like this. I would make dfco way more common and user friendly (at least on my own car). A lot of the controllable items like this could all be done manually like a switch to kill the injectors but I don't want to go there.
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Old 09-28-2013, 05:24 PM   #9 (permalink)
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Quote:
Originally Posted by davelobi View Post
Ya, funny that snap closing of the throttle plate (or tps) seemed to activate the dfco immediatly where a ease up on the throttle (as we are used to doing) made the computer think for a little while before deciding to activate dfco. Even more intriguing to me was if I was in dfco and I touched the throttle for even a brief second. The dfco would cut out and not come back on. The computer must be thinking something like "this guy may be ready to accelerate quickly" or maybe "doesn't know if he wants to accelerate or decelerate, better leave injectors on and ready". I don't know.
Or maybe the programming looks at the delta TPS to help determine if it should activate DFCO. Tapping the throttle gives a very small delta TPS when you let off again. Just a guess.
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Old 10-09-2013, 01:55 PM   #10 (permalink)
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CRX - '91 Honda CRX HF
Last 3: 63.1 mpg (US)

the ugly one - '97 saturn SL just sl,not sl1 or 2
Team Saturn
90 day: 44.15 mpg (US)

Vibe - '07 Pontiac Vibe
Team Pontiac
90 day: 44.24 mpg (US)

Hoopdie - '05 Toyota Corolla CE
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Colder outside? WAI? Winter fuel?

Still playing with the listening device ocassionally.
It seems my car does not drop into DFCO as easily or for as long as it did only a few weeks ago.

What changed? Outside air temp? Winter formulation gas already at the pumps?

Maybe time for the warm air intake I've been thinking about trying. I'll update it I get around to it and if it makes a difference or not as far as dfco is concerned.

Anyone have ideas about this? Anyone have evidence that a wai may help here?
thanks,
dave

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Get bored very quickly. Vibe, Saturn, and crv all long gone. Been a while but I'm back in the game, gunna see what I can do with this Corolla.
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