Pulse and Glide question

[Jay2TheRescue]

Originally Posted by PaleMelanesian

Are you sure the CRV doesn't have DFCO? My 1996 civic does.

I also say that unless it's in Neutral, it's not a glide. I doubt you'll see much gain from pulse-and-DFCO. Neutral is where the gains are. If you can get the transmission to unlock, you're most of the way there without shifting to N. You might try a tiny blip of the throttle right before letting off, to encourage it to unlock. The rpm should drop to near idle level.

I'm thinking P&DFCO might be more efficient as the engine ends up working closer to its peak effficiency, and then shuts off the fuel for a moment. Just a theory.

[theholycow]

Originally Posted by Jay2TheRescue

I'm thinking P&DFCO might be more efficient as the engine ends up working closer to its peak effficiency, and then shuts off the fuel for a moment. Just a theory.

Well, as I mentioned above, I had the same theory but reality worked differently...but maybe the unlocked-TC hybrid DFCO-glide will work better.

Maybe to differentiate from manual transmission P&DFCO we could call it GFCO (Glide Fuel Cut Off) or TFCO (Torque converter Fuel Cut Off) or UTCGDFCOCARU (Unlocked Torque Converter Glide Deceleration Fuel Cut Off Crazy Acronym Recursive UTCGDFCOCARU).

Other possibilities:
DIGUT (DIGUT Isn't Glide, Unlocked Torque converter)
DIGNUT (DIGNUT Isn't Glide, Neutral Unlocked Torque converter)
TONGUE (Torque converter Open, Not Gliding--Undue Effort)

[Jay2TheRescue]

Originally Posted by theholycow

Well, as I mentioned above, I had the same theory but reality worked differently...but maybe the unlocked-TC hybrid DFCO-glide will work better.

Maybe to differentiate from manual transmission P&DFCO we could call it GFCO (Glide Fuel Cut Off) or TFCO (Torque converter Fuel Cut Off) or UTCGDFCOCARU (Unlocked Torque Converter Glide Deceleration Fuel Cut Off Crazy Acronym Recursive UTCGDFCOCARU).

Other possibilities:
DIGUT (DIGUT Isn't Glide, Unlocked Torque converter)
DIGNUT (DIGNUT Isn't Glide, Neutral Unlocked Torque converter)
TONGUE (Torque converter Open, Not Gliding--Undue Effort)

I like DIGNUT. Shall we add it to the glossary thread?

-Jay

[ryandpotter]

I think my 2.3l ranger would qualify as either correctly powered or underpowered

Originally Posted by RoadWarrior

Pulse and glide, where the pulse is at about 80% throttle, and across the peak torque part of the rpm band, has your motor returning about 35% efficiency, then you glide at idle or engine off.

Cruising at "max mpg" speed has the motor in a very inefficient operating region, and you're just doing the "least worst" you can with it, efficiency may be as low as 15-20%

So done correctly P+G should be more efficient in just about any vehicle, the only exception to this will be something that is "correctly powered" or as most people would say "dangerously underpowered" meaning that you're running it at 80% throttle near the torque peak just to maintain highway speed.

[theholycow]

Originally Posted by Jay2TheRescue

I like DIGNUT. Shall we add it to the glossary thread?

LOL, that was a joke...it would be an inaccurate term since "Neutral" isn't really involved.

I suppose DIGUT could be taken seriously, though.

[sonyhome]

Originally Posted by PaleMelanesian

Are you sure the CRV doesn't have DFCO? My 1996 civic does.

My Del Sol does too, but it's MT, and the CRV is AT. How can you tell on AT?

The SG shows I'm spending gas (though in other threads with holycow & al there was some doubt the SG was reporting bogus data when in DFCO because the data reported is derived from other infos).
The other thing is RPMs go up as i accelerate downhill without pressing the gas pedal, but now I have a doubt for "D" , though I'm sure of that for "2" and "1". I think when the pedal is released, RPMs only go down because the slushbox shifts to overdrive. So that means in "D" I won't really be in some kind of neutral with the torque converter isolating the engine.

Originally Posted by RoadWarrior

Yeah if you've got a flatter torque curve, you can just get on the edge of it, I think around 85-90% of peak torque is where it starts to be good.

Dang! I was wrong. Flat torque curve starts at 3500rpm for the cr-v. 80% of max is at 3000rpm:

[theholycow]

Originally Posted by sonyhome

My Del Sol does too, but it's MT, and the CRV is AT. How can you tell on AT?

Same ways: Direct fuel injector monitoring, or feel for DFCO to quit somewhere near 1000rpm. I was unable to feel it in my automatic until I could watch it on the fuel injector monitor at the same time. Now that my butt is calibrated to feel it, I can.

The other thing is RPMs go up as i accelerate downhill without pressing the gas pedal, but now I have a doubt for "D" , though I'm sure of that for "2" and "1". I think when the pedal is released, RPMs only go down because the slushbox shifts to overdrive. So that means in "D" I won't really be in some kind of neutral with the torque converter isolating the engine.

The slushbox probably does shift to OD and unlock the TC when you take your foot off the gas, but as long as it's somewhere north of 1000rpm it should still be able to DFCO. If your TC is so sloppy that, on a descent where slight throttle would give you 2000rpm, you're down to idle then...er...I'd suggest getting a torque converter that transmits more power.

Jay has been able to figure out how to get his ScanGauge to detect DFCO in his automatic, using an X-gauge I think.

[sonyhome]

Yeah, I know, I need to get my butt in gear in implement the fuel rate meter.

And no, on a downhill the RPMs go up, the car doesn't drop to idle so the TC doesn't decouple the engine there. If there's DFCO then that would be more efficient to use engine braking downhill vs idle + footpedal braking.

BTW, on a 60mile mostly downhill drive, I got 40MPG on the CRV with neutral coasting. Not bad but not great either... last week end. Lost it all in traffic jam later, and back to my avg of 25-ish.

[R.I.D.E.]

DFCO can be subtle, but I think there are few cars that do not have it. Otherwise you would have fuel being dumped into an engine with very high vacuum and very low effective compression with no demand for power.

I know mine jumps to 1300 RPM (from 860) if you turn on the AC, so I guess it would be safe to assume the accessory loads on other cars would increase the minimum speed.

Without DFCO your car would probably not have very much engine braking.
It may be easier to recognize if you turned off all the accessories.

regards
gary

[sonyhome]

Originally Posted by R.I.D.E.

Without DFCO your car would probably not have very much engine braking.
It may be easier to recognize if you turned off all the accessories.

What?! turn off the DVD, the fridge, the GPS, the neons, and the hair curling iron? But driving would be boring then!!! I don't usually run the AC, and can't really feel any DFCO, in part because the AT just runs overdrive when coasting.

And I do find the engine braking rather weak on steep downhills, even in "1".