A case against pulse and glide
 

I drive the same vehicle on the same trip for 5 round trips a day now as a shuttle service for my college. Up until last week, the best FE I could get was 26.5mpg, and I could do it consistantly. I tried EOC a few times and was able to get 29.5mpg, which seemed resonable also.

But then I stopped doing pulse and glide and tried driving with a constant throttle, at 10% most of the time, and 15-20% on hills when needed at 3 points. With that, I was able to get 28.5mpg regularly, and 32.5 with EOC.

So that means that without using P&G I gained 7-10% gas mileage! I'm going to try out several different throttle percents over the next week and see what works the best, but I don't think that I will be using pulse and glide like I used to anymore.

I thought P&G was supposed to be more efficient since the engine is running at a more ideal speed, but apparently that's not the case. Does anyone have ideas? Can anyone with a SGII try this and tell me their results?

I'ma guess automatic trans. area not good for P&G, and not enough throttle on the pulse.

Confirmed. Best I could do around town with the auto saturn was like 40 w/p&g, when I put the stick shift in there I could get 60 no prob.

This really is a case against automatic transmissions if you ask me.

It's a Chevy Venture van, automatic, 3.4L.

I'm just surprised how much I read about P&G but no one talks about just constant driving. I guess automatics are the minority here though

Phew... I had found the same thing. Once into top gear and especially when the TC locks up, DWL has been better for me than P&G. I was just blaming my poor P&G technique.

Not in the minority certainly in the US, only 10% of cars sold were manual transmissions in 1998, and a lot of those were sports cars. We haven't been real serious about MPG here in the US.

2TonJellyBean -

We should be more clear on that. Maybe this distinction needs to go into the FAQ/driving tips section.

EDIT : i.e. the distinction that P&G may not be appropriate for automatics.

CarloSW2

i too have an auto V6(3.8). not convinced of pulse and glide, but i do just glide on the last mile home, getting of toll roads,etc.
preliminary results good so far.

I think there are significant inefficiencies in accelerating with an auto. The torque converter does not transmit energy as effectively as a clutch. As 2Ton said, keeping the TC locked up is probably best for an auto.

Don't P&G often
 

I don't really P&G often with either auto car in the Garage. Most of the time, my P&G involves EO-coasting down a hill at highway speeds, slowing due to drag, and starting back up at about 5 mph under the speed limit.

DWL on hills can be argued as a form of P&G, I suppose...

RH77

I had great success with P&G in my parent's 2006 Altima (2.5L - 4cyl). 40.15mpg versus their best highway mileage of 34.5 (CC). No wind, terrain was flat overall - but I was driving through south Florida hills (highway bridges over surface roads). No EOC - no A/C - tires likely were at 35psi - nighttime driving.

The SG read 40.2 - the on board FE meter said 40.1 IIRC ;) I have a picture of it somewhere :p

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So, instead of really putting the pedal to the metal - I gave enough gas until the TC locked up, then put down as much throttle as possible to prevent the TC from unlocking.

It's possible to get benefits - you just need to adapt to your transmission logic (as it will vary from car to car) :p

Auto gearboxes are VERY bad for accelerating :( On my car, even cruising at 50mph, uses 25% more fuel if the torque convertor is unlocked, compared to when it is locked. (figures by SuperMID which I recently installed).

I'm looking to see if I can find a way to have a lockup-at-will button, which will get a lot of use in town, but, so far I can't find out how to do it. I know there is a solenoid, but I think it is under a metal cover as part of the gearbox!

I can agree that DWL and coasing when it's beneficial may count as a form of P&G, but the idea that pulsing and gliding for flat terrain jus doesn't work for the 2 autos I drive.

Same average speeds and weight?

Yep :thumbup:

treb, do you think that if the Altima had taller gearing the advantage of using P&G techniques would decrease?

I too tried P&G with my auto Saturn and actually did better staying at a constant speed, but like others it could have been me.

I've tried pulse and glide in my Cavalier which is a 3 speed auto and seen some benefit. My biggest problem is trying not to mess with traffic too much on my way to and from work. Speed limit is 55, so I pulse to 60-65 mph and glide back down to 50 then slowly accelerate back to 55 until I see another chance to pulse. Using this method, I went from an average mpg of 34 on my commute to 37-38 depending on how much I can use it. I wish I had a manual though, as it is a pain to do with auto, and the benefits would be much greater. Anyone want to swap in a metal masher for me? :p

Honestly, I couldn't tell you.... The final drive ratio is 4.425... It could be better, but it's pretty tall be comparison... Although, the thing does have a lot of torque...

I really think it comes down to the transmission shift logic. Which is why there is no one set P&G technique that fits all ATX's. But I'll bet the general rule of thumb is to keep that TCC locked up as much as possible and always accelerate faster than stall speed (which should be really easy on OE torque converters).

Yes and No
 

My experience depends on which car I use.

My commuter is a manual transmission BMW and it thrives on *aggressive* pulse and glide. By that I mean 1/2 throttle surge to 75 mph then glide to 60, rinse and repeat. I'm not shutting off the engine when I do this--just coasting with the clutch in at idle. Good for an extra 2.5 mpg compared to a reasonable DWL at 60 MPH. One reason could be VANOS variable valve timing and variable muffler restriction that both kick in at higher engine speed and power setting. The engine also is apparently much happier when pulling hard than when maintaining speed.

The other vehicle is a Venture with the 3.4L as mentioned above. The good news is that these GM transaxles short shift and lock up their torque converters very willingly if you keep a light touch on the throttle at appropriate speeds. I agree that pulse and glide doesn't seem to work well. The van doesn't seem to glide well at all. On the other hand the final drive is so long-legged, the engine's not much above idle when you're cruising anyhow. The best thing I did was look up the light throttle upshift and lockup speeds so I could feather the accelerator and take advantage of them.

I'm not surprised by this at all, and I wouldn't call 1/2 throttle aggressive. Consider the engine maps here. Note that peak efficiency occurs around 2000 rpm, and requires giving it 30% of power, of which the total power available at that rpm is 40%. Which means that you are giving it 3/4 of available power at that rpm. Not sure how that relates to throttle, but it's probably at least half.

FYI, I've made a pulse and glide (for manual transmissions) fuel economy calculator here. It will also calculate fuel economy figures for constant speed in gear driving.

In my own recent experience, P&G only seems to help if I'm not going fast enough to lock-up the TC. It really helps when I'm not able to be in top gear due to the traffic speed.

P&G works for me in my automatic Cavalier. Just have to accelerate slowly and do small P&G's within a larger one. Automatics still have neutral BTW.

I usually don't P&G because it will take me out of lean burn territory.

Done that for mine...I haven't seen any perceptible increase in average FE with the colder weather. It appears to be most useful for climbing long grades at lower speeds, but I don't have that many on my commute. It's pretty tough to beat the stock PCM program with it.

My guess is that the best acceleration with a TCC lockup switch on a warmed engine is to get up to 25 MPH in third slowly, then keep it in third, lock up the TCC, accelerate hard to 45, back off, unlock, shift to fourth and lock up again -- basically a hybrid of optimum acceleration for an auto and a stick (easy for the auto, hard for the stick). That's what I've been doing lately, but again it's tough to see any difference. Unfortunately, it's easier to mess up the shifting on an auto than a stick, because the gear selection isn't readily apparent without looking at the indicators (D/2/L on the shifter and O/D off light on the instrument cluster).

As far as pulse and glide...my car doesn't coast long enough to make it worthwhile unless I'm headed downhill anyway, so that's when I'll do it. Otherwise, I'll keep the engine lit and TCC locked up if I can, and just drive at as near-constant an engine load as is practical.

I'm glad you said it, I was beyond attempting to explain constant gas.

But you're right, it's quite efficient, works better on some cars than others thou.
My 91 bmw the pedal is stiff enough for it, you can hold that gas in the same spot until your leg cramps and then some, I'm talking 20 and 30 minutes at a time and even longer if you feel like it. But take my truck and the gas pedal is so light it's just not possible because I can't feel it.

I think constant gas is better than cruise control, also the higher compression the engine, the better it works. On long drives it works also if you get used to making only tiny adjustments and hold your foot in the new position for prolonged periods of time.
So for example if you back off just a tee, then wait for the engine and the speed to settle in before you adjust further.

Hell yeah constant gas RULES, btw I like that expression, constant gas.

By the way, try this:
- Remember the positions on the pedal (constant gas) it takes to maintain 45 mph for instance (also 35 and 55, 65 as well).
- Now, when accelerating from a standstill, if say the speed limit is 45, use the constant gas position that you would use as if you were already doing 45 throughout the entire acceleration process.
> I do this a lot on my truck, it does take time, you need somewhat of an open road with little traffic, won't work down town lol.
>> This also comes in extremely handy on highways where the speed limit changes, say you're at 35 constant gas and you know the speed limit is going to be 45, with proper planning and once you remember the spots on the pedal you simply put the pedal to the 45 spot and lalala.

Works a LOT better than pushing it there and then cruising.

It will take time, I think several miles before hitting the next speed is not unusual, and have to be patient for more than a few minutes.

I get off on that crap, just listening to that engine slowly work its way to the pre-determined speed.

I'm new to the site. What does EOC stand for?

Wecome to GasSavers: EOC refers to engine off coasting. It is also known as Codfishing, which largely started as a joke. It essentially refers to turning off your engine, putting your car in neutral and coasting to extend your mileage. It can often be used to long coasts to lights.

However, it has some risks. First it is illegal, some places. Second, if you have power brakes or power assist, which almost all cars do, now, then you only have the assist for one or maybe two uses of the brake pedal. After that the brakes still will work, but you have to press substantially harder. Third, if you use the ignition key to turn off the car, you can get the key and steering wheel lock caught in a fixed position, and encounter difficulty with getting it unlocked, while your rolling towards something you don't want to be. This tends to cause increased heart rate and uneasy passengers.

To EOC more safely, you should put in an injection cut off switch or something, so you can turn off the engine, without utilizing the key. On my car, I also removed the wheel interlock switch, so I can't get my steering wheel locked up, if I am doing EOC.

It is like a great many things, it seems to work better in some cars, than others, it seems to work someplaces better than others and sometimes it either seems to not work or not work any better than other things. In that respect each person is a unique experiment in terms of where they are, how they drive and what they drive.

Try it, if it works, for you great. If it doesn't then stop and try something else.

Where I have been very surprised with EOC is in driving hills. It seems if you go up the hills at a little slower, non accelerating rate, you can achieve pretty high mileage, overall, by EOCing down the hills. However, you have to always consider safety in speed and control, as being far more important than a few miles per gallon improvement in gas mileage.

Could you let us GM mini-van owners know what those upshift and lockup speeds are?

Wayne

U Van Shift Schedule
 

Here goes:

At 12% TPS (throttle position sensor) value:

1-2 shift will occur at ~13 mph
2-3 shift at ~ 20 mph
torque converter clutch apply in 3rd gear starts at ~ 23 mph
3-4 shift at ~ 40 mph
torque converter clutch apply can start at that same speed in 4th.

At 25% TPS the shift points are 20, 31 and 51 mph, respectively.

Also at 25% TPS the torque converter clutch applies can start at 34 mph in 3rd gear and 47 mph in 4th.

At 50% TPS 1-2 and 2-3 are at 30 and 52 mph. 3-4 won't happen at 50% TPS :) .

With the throttle closed, 4-3 happens at 36 mph and 3-2 at 18 mph.

This should give you something to chew on.