Pulse & glide not always better than steady speed in-gear?
 

I've read a number of posts on here over the years in my efforts to learn the best possible way to drive my stick-shift 2010 Hyundai Accent. I figured out a good routine for suburban driving without having any experience on the highway. Lately circumstances have changed and now I'm on the highway a lot. So I had to relearn how to get optimal MPG.

I did pulse & glides throughout a tank, pulses to 70 MPH (a little more when on a hill to reach the top) coasting down to 55 repeatedly on the highway and pulses to whatever I could get up to in town in order to coast down to 0-20 before applying brakes for lights or traffic. This tank got 36 MPG overall.

On the next tank I removed the pulses and most of the glides except for significant downhills and when slowing for lights and traffic. Instead I stayed in 5th gear, keeping my throttle % at a point that maintained 55-65 MPH on the highway and the speed limit in town. This tank got 43 MPG overall, a very significant improvement.

On the first tank I was getting 20 MPG during highway pulses and 250 MPG on highway coasts but the pulses would take a while due to my car's weak engine. It had me wondering if pulse & glide is better suited for cars with more powerful engines that could go from 55 to 70 MPH more quickly. With the throttle position held steady on the highway holding 55-65 MPH the MPG reads 39-42.

I've gotten the impression from what I've read on here that pulse & glide is always better than staying in gear at a steady speed but I don't seem to be reaping the benefits of that somehow. I know engine-off coasting is a bit more effective than leaving the engine on but I'm concerned about the extra wear and tear. Perhaps staying in gear is better in some cases.

Your pulse window and speed is way to high. 55-62 seems to be the sweet spot for P&G. Any higher and you start meeting higher wind resistance = speed drops faster = less gain from P&G. I drive 70-75mph on the freeway now, and I never P&G. I found using it over 65mph reaped same results as you. Lower MPG.

this depends on the car
 

My civic has a high rpm, and peak power at 5500 rpm. Maybe for that reason, the mileage is much better with pulse and glide, than it is with driving at a steady light throttle.

I've tried the latter several times, averaged about 10 mpg worse, and immediately went back to pulsing and gliding.

For my car, I think the difference between going an even speed and pulsing is not that much, compared to the great benefits from gliding. Also, pulse & glide is more effective the longer the glide, thus with better aerodynamics of the car.

Back when I was driving Black Widow, which is not an aerodynamic vehicle to say the least, I saw an immediate 8 mpg jump when I began EOCing to lights.
That encouraged me to begin P&Ging, and I ended up gaining another 8 mpg. I started out at around 42-44 mpg, and was able to pull over 60 mpg on one tank.

I stayed off highways and would P&G from 55 down to 35 and back, and it worked awesome for that car.

Now that I have Turtle I only EOC to lights. I have never tried to P&G in the Insight, even though it's a perfect platform for it since it autostarts. Problem is that it draws a lot of juice when the motor is off, since I leave for work when it's dark and return home when it's dark so I have the lights on pretty much every time I drive it. So I have to charge the 12V every night just to EOC, or it runs down the tiny 12V battery, which also runs down the IMA battery.

How many RPM's in 5th at 55MPH??

Terrain dictates. Every platform, road and driver have differences. The conditions you're in and your goals at the moment (how much of a rush are you in?) are even more changeable, so the effectiveness of different techniques changes with them. YMMV, as it were.

What kind of instrumentation do you have? Instant and trip are the bare minimum, but short trip is where you can compare different conditions and techniques. Comparing your morning commute numbers to other morning commute numbers will teach you a lot more about conditions and techniques than just tank to tank and instant mpg numbers.

Pulse downhill and coast uphill

Pulse up, glide down dammit!

I don't know about you but my car gets bad MPG uphill...
Much better downhill....

I only run the engine down hill, more MPG no?

Depends on how the vehicle acts on hills. My car is terrible for gliding up hill but great for going downhill. Of course, I try not to P&G often, but even when DWL I can see the results on hills. Every day I drive to I-44, and there is a huge hill that I go up and down to get there. Going down I can get up to 60 (speed limit 50, but who cares, long uphill right after) then going up the hill I get down to 45 MPH. On the highway I just DWL because at those speeds and city traffic, there is no reason to P&G. Once at school, I can P&DFCO (automatic makes my DFCO last down to about 17 MPH) around the circle and receive great numbers, going from 27-23-27-stop.

What I'm getting at is that all vehicles are different, just play around with how you think it should be driven, do what feels best, try new techniques and see how they work out for your car. Don't do anything that makes you feel uncomfortable (EOC in auto for me) because then you will be a danger to other drivers.

Speed variation is always an aerodynamic penalty over maintaining the same average speed .. under any and all methods .. any speed .. etc... This is a consequence of the exponentially increasing wind resistance.

P&G works as a net vehicle benefit when some other effect of the P&G overcomes the aerodynamic penalty for speed fluctuations.

One of the big effects that can beat the wind resistance penalty many times in P&G is the net ICE operating efficiency... So look for the BSFC for your ICE and try and line up your P&G with the best net ICE operating efficiency.

As others have said , this is easier to achieve at slower speeds .. because the larger the aerodynamic penalty the harder it is to find some other drive method benefit to overcome them... and wind resistances increase very fast with faster speeds... Wind resistance force increases @ V^2 .. wind resistance power increases @ V^3 ... 10mph to 40 mph is 16x more wind resistance force and 64x more power... but only 4x faster.

Thanks for the info IamIan. It seems like my little hatchback is not very aerodynamic and I can definitely feel the resistance at higher speeds. I seem to do best around 35 MPH with this car but I'll look into engine efficiency.

RPM at 55 MPH in 5th is around 2,500.

I've just been looking at instant MPG and then seeing what the results are when I fuel up. I will try setting short trip MPG on my Ultragauge. Thanks for the tip Charlie!

The best results I've had with various manual transmission vehicles has with pulse and glide from 30-45 EOC back down to 30 repeat. I try to drive as close to this as my situation and time permit.

In my experience, pulsing over 60mph will generally have a negative impact on your economy no matter what else your doing. Since you have an Ultra Gauge you should be using engine load % to help you determine how hard to accelerate for most efficient results. I find 69-71% load yields optimal results in my 3.4L Tacoma while around 85% is better in my Dad's 96 Ford Aspire.

Unless you can find a bsfc chart you will have to determine this through trial and error.

In ideal conditions I can get over 40mpg in my 4x4 v6, but conditions are rarely ideal!

I'm interested in how you make the determination of what %-load is optimal. On my UltraGauge the percentages are ephemeral since acceleration periods are usually brief, and are very sensitive to throttle position.

I haven't been able to find a BSFC chart for my engine (2.0 L Duratec in a 2005 Ford Focus), so I have been trying to hit 75%-85% as a generic best guess, and figuring that 65% to 75% is probably good at lower than 1300-1800 RPMs. Guesswork, as I said.

But backing off the pedal just the smallest tad drops me from, say 95% to 60%, so it's quite hard to hit my guesswork sweet spot.

(I also notice that, while accelerating, I need to progressively add bits pedal displacement to keep in my target %-load range.)

Sorry for the digression. My question is in the first sentence.

% of engine load
 

The same for me. I go up to 90% MAP on pulses, about the same as 90% engine load. The results at 80% have not appeared nearly as good, based on trial & error while keeping close watch on the ultragauge trip average mpg.

I saw a report that greater increase in fuel is triggered by quicker change in acceleration, so I've endeavored to sneak up on 90% MAP rather than going there instantly. However, I don't know if this makes any difference.

The more instant you blip your throttle, the more fuel you will use, at least if your car is drive by wire. If I gently squeeze into the throttle, RPMs go up slowly, and I get up to desired gal/hour (3). When I quickly go onto the throttle, for about half of what I do when I slowly squeeze, the RPMs jump up to 2.5-3k and I get about 4 gal/hour for a few seconds, then down to what it is supposed to be, which is about 2 gal/hour.

I haven't found any BSFC charts for my car in particular, but others with the same displacement seem to say that between 3 and 4k RPMs is where I get the most torque per drop of fuel used.

increasing to peak rpm, not beyond
 

Perhaps you're simply overshooting the rpm, and then coming back down to a desired peak, which is not the same thing as gradually increasing to that peak.

I'm speaking of either quickly going from 1500 (for example) to 2500 rpm right at 90 MAP, and then gliding, vs slightly more gradually going from 1500 to 2500 rpm, i.e. more gradually up to 90 MAP which still only takes a few seconds, and then gliding. There is only a slight and subtle difference between these, and no overshooting involved either way.

I know what you are saying, johnlvs2run, but I remember reading somewhere that immediate change in engine load shifts the car into a different VTEC mode, thus using more fuel than gradually changing engine load.

I do know what you are saying though, I haven't played around too much with it though, so that may be the case. I'll check in more on it later this week.

Yes, that's what saw as well.

I'm getting much better P&G results now that I'm using lower gears to pulse instead of the overdrive gear. I haven't done a full tank yet but I'm pretty sure I'm getting a 3-5 MPG increase over staying in gear. All of that rapid acceleration can't be good for the tires though and I'd probably drive passengers nuts if I drove this way with them in the car. Haha!

I'm starting to bump start more often as well but I'm wondering, has anyone had problems arise from doing a lot of bump starts?

Thanks again for the advice.

Bump starting killed my clutch after only 41k miles! Of course, I had about 166k of rather sporting use on that clutch when I started EOCing...

Bump starting will wear it faster than you already are. If you're rough on clutches, this is bad. No problem if you're smooth. If you want to become smooth, it's more practice!

Regarding P&G at different speeds, I still have an improvement of 2-3MPG doing P&G at higher speeds over non-P&G. This is all highway, with little traffic volume. I usually am pulsing to 75 and gliding to 65 (sometimes 60). DWL, pulsing as I crest a hill and gliding down. I know I would do better at lower speeds, but can't go slower without being a hazard.

Anyway, my experience is that P&G still helps at higher speeds vs. no P&G at the same general highway speeds.

Pulseing down hills after gliding up them works very well in my truck because of the weight, doesn't slow down too much and picks up speed very quickly at only 1700 rpm

Just another thought - The map might be leaner at steady cruise, or using O2 control might keep it 'at it's leanest' if the map has no leaner than 14.7 (thus making closed loop best).

And of course, lean burn (if supported) will likely not be entered if you are pulsing and gliding.

There won't be a hard and fast rule for every car - though the principle for pulse and glide is sound - using inertia as opposed to steady power.

That's why I only hit the kill switch when coasting to a light, or down a (tiny Florida) hill. My main focus is getting into lean burn and staying there. Check out the maps below to see how many times I have modified my route in search of one that offers the most time in lean burn.

There is no direct route between my house and my job unless I strap on a jet pack. The shortest routes have the most stop-and-start traffic, which kills the mpg of an Insight. The long straight stretch of I-4 takes me miles out of the way. I have tweaked my route multiple times since buying the Insight, and when my wife carpools with me I also have to drop her off, which throws another point onto the route.