A case against pulse and glide

[Mighty Mira]

Originally Posted by css28

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 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.

[Mighty Mira]

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.

[2TonJellyBean]

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.

[Hateful]

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.

[rpm]

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

[GasSavers_Bruce]

Originally Posted by landspeed

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!

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.

[8307c4]

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.

[GasSavers_SD26]

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

[Gary Palmer]

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.

[FireEngineer]

Originally Posted by css28

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.

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

Wayne