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Old 03-24-2014, 06:13 PM   #11 (permalink)
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Quote:
Originally Posted by bestclimb View Post
I think this has been tested (though not necessarily for a subaru with it's added AWD drag), leaving it in gear pulsing then coasting down in gear with dfco. from what I remember the coast downs were short enough that coasting in neutral with the engine idling was more efficient.

The wear from a bump start is pretty negligible given the forces involved. With a bump start you are getting the weight and drag of the moving parts of the engine going. Compared to just getting the car moving you are getting the whole mass of the vehicle moving.
Yes, in most cases, coasting in neutral is more efficient than coasting in gear/dfco because neutral coasts typically last longer.

My observation on my subaru (possibly other subaru's), when i shift to neutral and the rpms drop....around approximately 1000rpms, the fuel injectors cut off for a split second.

My theory is that when i am coasting in neutral, if i keep blipping the throttle around the 1000rpm sweet spot, i am able to coast in neutral while simulating Engine OFF coasting vs. coasting in straight neutral.

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Old 03-24-2014, 09:38 PM   #12 (permalink)
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If it works out that a series of blips costs less in fuel than just idling, a solenoid acting on the throttle cam could automate it.

I think the ultragauge is reporting more injector time off than we are actually having though. (I don't know for sure though) it seems like the injectors are cutting off during the drop and the UG is showing that cut off to be longer than reality.

How does Subaru handle the transition from DFCO (clutch in/neutral and foot off throttle) to idle? does it go right back into closed loop. or remain on an "initial idle" program for a moment.
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Old 03-24-2014, 11:33 PM   #13 (permalink)
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This is pretty interesting. I've noticed that in my Yaris it only goes into DFCO (also 9999mpg on my ScanGaugeII) during actual engine braking in gear, and I can feel the engine braking. I've never seen DFCO outside of engine braking. I will say that I have seen DFCO come on for a split second when I shift to Neutral, but I think that has to do with a very brief moment of engine braking before the coast.

Looking forward to your results with these tests.
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Old 03-25-2014, 04:52 AM   #14 (permalink)
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I accellerate and engine RPMs are up (lets say 2500rpm) and then you put car to neutral, it seems logical that you get fuel cut - car ecu sees that you want RPMs to go down to idle speed - so to drop rpms, it cuts fuel. Why it should send fuel to injectors if RPMs must go down? It decellerates engine using fuel cut. When engine speed goes to idle speed, injectors are turned on again - otherwise it would stop.

I have verified this with two cars watching mpguino (Mitsubishi Eclipse and Audi A4 diesel).
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Old 03-25-2014, 06:54 AM   #15 (permalink)
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Quote:
Originally Posted by WilliamYH09 View Post
I will say that I have seen DFCO come on for a split second when I shift to Neutral, but I think that has to do with a very brief moment of engine braking before the coast.
ScanGauge indicates DFCO between most every gear shift on my Corolla. Not sure if it is actually happening though?
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Old 03-25-2014, 03:13 PM   #16 (permalink)
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I did some data logging last night on my torque app. I'll post up graphs today.

I'm noticing the dfco may actually be more dependent on throttle input instead of rpm (my original theory).

bestclimb appears to be correct in that the car goes into dfco for a split second when I step off the gas pedal.

Therefore, if I keeep blipping the throttle, I can extend the dfco event for longer periods of time. However, the efficacy seems to diminish when I reach speeds lower than 20mph
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Old 03-25-2014, 08:33 PM   #17 (permalink)
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Data Logging...theory %50 confirmed?

Here are the graphs of the data logging I did with Torque App last night. It pretty much 50% confirms my theory is valid ( I still want to hook up my MPGuino and Voltmeter to the injectors to be 100% sure).

It appears that the engine goes into DFCO for a split second when I step off the throttle (red circle). Throttle position goes down…fuel flow drops to 0 and instant mpg jumps up.

Then I keep blipping the throttle to extended the DFCO event for longer periods of time. Fuel flow drops down to 0 and instant mpg jump up to 255mpg (the max Torque App displays)


Thoughts? Comments? Constructive Criticisms

I also did more ABA testing.

I changed up my testing method to eliminate more variables. This time, I drove up to 50mph, shifted to neutral to coast, then when I hit 40mph, I hit RESET on Torque, then when I hit 20mph, I hit RESET AGAIN. This way, I only measure the amount of fuel used while coasting. I eliminate the variable of my foot accelerating too hard.

I also measured using 6 decimal spaces, to allow more accurate detail in fuel used.

A1 Runs – Straight neutral coasting from 40mph down to 20mph
0.003973
0.003607
0.003754
0.003500
0.003657
0.003907
A AVERAGE – 0.003733 gallons/fuel used

B Runs – Blipping throttle while coasting from 40mph down to 20mph to simulate EOC event
0.0015200
0.0007780
0.0001470
0.0009400
0.0007230
0.0006480
B AVERAGE – 0.0007926 gallons/fuel used

A2 RUNS
0.003673
0.003458
0.003368
0.003382
A2 AVERAGE – 0.00347 gallons/fuel used

A averages – 0.00362 gallons used
B averages – 0.0007926 gallons used

78.11% improvement over traditional P&G

Obviously, using straight EOC will yield better results.

I also data logged Air/fuel ratios too if you guys want to see that graph.
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Old 03-25-2014, 09:58 PM   #18 (permalink)
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This might be one of those times where having an external fuel cell would be helpful.

Interesting. It's an appealing thought... Pulse-and-glide idle during your pulse-and-glide drive. Yo...
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Old 03-25-2014, 11:33 PM   #19 (permalink)
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Tonight while at work (pizza delivery), I experimented a little with this.

First off, with my automatic, if I coast (engine on neutral) and then shift into gear when coming to a stop, the car will not engine brake and go into DFCO unless I blip the throttle. Also, usually no matter what gear I'm in or speed I'm going, if I let off the throttle and it doesn't immediately go into DFCO, I can blip the throttle and it will then go into DFCO.

Anyway, tonight I decided to blip the throttle during a few coasts, and sure enough, my ScanGaugeII read 9999mpg after most blips. The problem seemed to be figuring out how hard to blip (light tap or a bit harder tap) and how often to blip (every 2 sec. maybe?). Whether or not fuel was cut off during coasting when my ScanGaugeII read 9999mpg, I don't know, but from what you've tested so far, it seems like blipping the throttle while coasting works.

If further testing confirms this, I like bestclimb's idea on automating it, though I don't know much about setting something like that up.

Nice work.
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Old 03-26-2014, 02:45 AM   #20 (permalink)
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Quote:
With modern fuel injection systems any time you take your foot off the gas the injectors will turn off until a preset RPM is reached and then they will turn back on. On the cars I work on the turn back on point is about 1800 RPM cold and say 1300 RPM hot.
So if you take your foot off the gas in neutral the engine will get zero fuel for that split second it takes to get near idle.

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