driving technique: pulse & glide (long)

[diamondlarry]

as for the ScanGauge, you're lucky your OBD2 protocol supports the data feed after engine-off. apparently there are 2 protocols (ISO bus vs. CAN bus). both shut down the ScanGauge at engine-off, but ISO takes much longer than CAN to re-initialize when switching the key back on, effectively giving ISO (me) no coast-down data (and skewing my mpg averages down as well if i do much engine-off coasting).

In some ways my Scanguage is almost annoying. I have already been sitting in my driveway with the key on and engine off right after a trip and I can push the button on the Scanguage to bring it out of sleep mode and I can watch the trip mpg go down.:-( Although in some ways it's kind of interesting to watch how fast the engine cools down when it's not running.

[Matt Timion]

I was thinking about this tonight. I realized that hooking up the stock honda cruise control mechanically would not be difficult at all.

Here is how the honda cruise control works. Instead of the cruise control actuator pulling on the throttle cable like in other cars it is actually hooked up to the gas pedal. The pedal has an extra bracket on it. It's all cable driven.

So if we could figure out a way to change the code of the cruise control ECU we could actually add a second actuator that is hooked up to the clutch pedal or clutch cable. When it is gliding it will engage the clutch and it will actually be in nuetral.

The downside of course is extra use of the clutch. if I could get 80mpg out of it however I think changing a clutch more often than usual is worth it.

[jamescartagena]

Decided to try a modified version of the pulse and glide in my F150 truck for the past two days. I used to always keep the cruise control on 55 and drive to and from work like that. Now I accelerate up to 60 then let off the gas until it drops down to 50. Then I do it over again. I don't turn the engine off. My rpm drops from 1550 to 1100 when I glide. Going up hills, I just keep it at a steady 55. It really seems to help. I don't have a scangauge (saving my pennies for one) but the farthest I could go on a 1/2 tank of gas was 319 miles. Today the odometer read 349 miles on a 1/2 tank. I started doing this after I had already driven 100 miles on the existing tank so I will have to redo the test next week when I fill up. But anyway it shows promise! Thanks for the tip!

[SVOboy]

Is the f150 an automatic? Diesel? Two tanks? That's exciting news though, I may need to try this on my road trip tomorrow night and to pick up and engine on monday,

[MetroMPG]

it would be better to go to neutral for the glide than just to let off the gas. letting off in gear means you've got engine braking, so the glide may not be long enough to compensate for the reduced mpg of the pulse.

just a thought - i didn't try it with my scangauge.

my very non-scientific results showed an 8% efficiency gain gliding in neutral with the engine running. it would be significantly less than that with engine braking factored in.

though i suppose even a 1 or 2% improvement is better than nothing...

[SVOboy]

The reason I asked about auto is from your first comment. If he was auto shifting into neutral then back into gear is no good, you lose a few mph from the initial getting the engine spinning again stuff.

[MetroMPG]

i don't know about auto transmissions, but in the manual, you should blip the throttle as you release the clutch to re-engage the gear at the proper rpm. that way there's no sudden engine braking, drivetrain shock or clutch wear... "matched-rev shifting" - same principle as heel & toe downshifting.

you could probably do the same with an auto tranny, but i'm not sure. (in reviews of sports cars with paddle-shift slushboxes, you often read about how the ECU blips the engine RPM up to the proper speed as you engage a lower gear, so it's out there.)

but i'd personally be reluctant to shift in and out of gear at highway speeds with an auto unless i knew it was OK for it.

[SVOboy]

Yeah, if I "blip" it shifting into gear it doesn't do anything. It starts out in first gear then shifts up is the problem. Mehbe it's just my piece of crap, need to swap to manual.

[MetroMPG]

another potential downside to pulse & glide: seems logical to me that it's harder on machinery to run it at a constantly changing speeds, vs. at a constant speed.

repeatedly changing a car's speed with this technique, while it may use less energy, strikes me as more likely to promote wear in the drivetrain.

i have no idea what the difference may be. just putting the thought out there.

[Matt Timion]

My wife said that in her Mitsubishi Galant the cruise control was set up to behave in this manner. She said it always went above the target speed and then coasted down below it to only climb again. It might be worth looking into.

As for the wear on the engine, you might be right. This would be a good reason to not do this all of the time.