Re: Fuel Injector shut-off while Coasting
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As to the OPs question of if DFCO is only on older cars, in 4 years at school for automotive tech (and a few more working in shops outside of school and on my own) I haven't yet found a fuel injected car that didn't DFCO. Some have a delay or more criteria to be met before it'll happen, but they will all do it. Air going through the engine, even without fuel, picks up a LOT of heat, while it's not the 1000+f with load, it doesn't cool the cat off fast enough to be a problem. the SG does register DFCO on my fiancee's 03 protege and it'll DFCO from 80 till you can't keep the revs up (including downshifting the auto to keep them up). coolant drops 3-4 degrees on a cool day but it still DFCOs. |
Re: Fuel Injector shut-off while Coasting
2002 Civic Si, and the 2004 Monte Both do it. The automatic in the Monte makes it mush less likely to happen tho. Not really coasting, it only happens under engine braking.
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I have a 2012 Mazda 3i (skyactiv) with 6sp MT and I can confirm that my fuel cuts off when coasting. I am using the APP Torque on my Tablet with a BT OBD-2 sensor. At idle (not coasting), my fuel rate is ~0.24 gph and it goes to 0.00 when in gear and I release the throttle.
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Cool. Have you detected any conditions where it does not do it so readily, such as a recent shift or electrical load from wipers and headlights? How low does RPM get before it cancels fuel cutoff?
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The only time that I noticed that it does not cut off is when you are shifting and you are in the wrong gear, for example, your doing 34 mph and lugging in 6th gear, then shift to 5th, but since the engine is still not under a proper load, you need to shift to 4th gear, then it will cut off, BUT if you shift to 5th and crack the throttle for a second, it will cut off. Another thing I noticed about the cut-off was when you are coasting down a steep hill (doing a high rate of speed such as 64 mph) and you push in your clutch (not in any gear) the flow rate goes from ~0.24 gph to 0.00 intermittently, the only reason I did not want to be in gear was that there was a hill in front of me that I needed the momentum to go up, really did not want to reduce my speed at all (love the 0.27 drag coefficient of this car!, it even has a belly pan built in from the manufacturer!) I never saw the cutoff go off, even in gear, when I was about to stop at a stop sign, it would stay off till I would stall if I did not push in my clutch! Without the information from the OBD2 and the Torque app, I would never find out this info, it is a great way to get the info you need to drive your car to get the best mileage and recommend it (instead of the scan guage ) to anyone interested finding out more info about their car to optimize mileage. Jim |
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I find coasting neutral uses less fuel, due to the fact that on a hill you will travel faster and therefore further as the engine does not brake and slow the car down like it does in gear. There are plenty of large long hills here so the savings have been apparent for quite some time!
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During the time in which you're doing it (which is technically engine braking, not coasting, even if it's so little braking that you can't feel it) you will use zero fuel. However, depending on the road ahead, neutral coasting can often beat DFCO when you look at more than just instant MPG. DFCO needs the engine at higher RPM with more friction loss, more reciprocating loss, and a bunch more pumping loss. That energy comes out of the vehicle's inertia. Further on up the road you'll need to burn more fuel to make it up unless you were already going to brake anyway. Depending on the vehicle, the road ahead, and whatever other conditions, that energy can be more than the amount of fuel required to idle the engine or less. Very often it takes more fuel to re-accelerate the vehicle after DFCO than it would have to idle the engine for neutral coasting. That's merely a narrow-view technical analysis of the fuel usage at stake using math and experience; if there are other issues at stake like legality or safety, those concerns come first. |
No I get what you mean, the need to accelerate arrives sooner in gear, as the car will slow quicker, and accelerating uses more fuel than idling in neutral for sure.
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Idle jumping around and mention of lean sounds like the focus has a vacuum leak, which is not unusual for them (I'm struggling to fix my V6 Contour which is also known for vacuum leaks).
If the FI shuts down, the engine is off - you ought to be able to hear/tell when your engine is off. I glided with my engine off but in gear (Contour V6 with 5 speed manual) a few times (to slow down at the bottom of a hill that has a stop sign) instead of staying in neutral like I usually do)) and it's obvious that the engine is off...the car slows down faster and you can hear the lack of detonation. I have a long hill in a 45MPH zone on a country road on my way to work. Car keeps going right around 45MPH while gliding, so I often shut off the engine and glide in neutral..brakes and steering work fine (I turn it to "On" after turning the engine off). |
My 2014 Mazda CX-5 GT (automatic) cuts off fuel as soon as I let off the gas (on highway), but the torque converter is still locked, so in effect, it will engine brake and slow down my car more than I want it to. It's okay on downhills where I would need to slow down anyways, but not so good on flats. It would be a better approach if I could choose to let it just idle (using some gas) and disengage torque converter, which is like putting gear in N while coasting.
I read in a 2014 Mini Hardtop user manual, they do exactly this in Green Mode. When speed is above 30 MPH, and you let go the throttle, torque converter is disengaged and engine goes idle (uses some gas) while gliding, same as putting in N. So I guess it varies by manufacturer how they implement the gas paddle off situation. |
That's another reason I hate auto's, you just can't drive the way you want to drive. I use neutral a lot around here.
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Manual transmissions will DFCO too.
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I appreciate that, its just easier to coast in neutral in a manual.
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