coasting vs Miles / Gal

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coasting vs Miles / Gal

July 16, 2014, 10:38:24 AM

While I owned an 08 explorer, i noticed when going down hill the transmission would seem to go into a neutral position, this is only an assumption based on what the tac displayed which was close to idle rpm's.

I usually get about 24mpg at highway in my 20th but recently during long road trips i would experiment on each available opportunity of downhill situations and put the trans in N. I am seeing anywhere from 15% to 20% increase in miles per gallon by doing this, however i dont think / feel continuing it would be good on the AOD so i no longer do it.

i am now bothered by the fact that i can get to this better efficiency if i want to but stand a chance of breaking something by shifting manually.

can we have a discussion on a mod to get this extra mileage on our cars?

my first thought is to use a vac operated gate valve to close the flow of transmission fluid by adding this "T" gate valve to the return line of the transmission. Wouldnt this stop flow and simulate the torque converter not having the ability to move the secondary impeller?,, effectively putting the car in N? perhaps on the supply line instead although i dont see the relative difference.

could a cable driven gate valve using the TB / gas pedal position be used to allow transmission fluid return flow?

are there other options to simulate or introduce a N condition on the transmission without actually shifting to the N gear?

coasting vs Miles / Gal

Reply #1 – July 16, 2014, 08:16:12 PM

I don't know about doing that. By stopping the flow, it would seem like it would cause the trans to burn up.

coasting vs Miles / Gal

Reply #2 – July 17, 2014, 03:28:42 PM

Easy fix... swap in a 5speed...

i think you would gain more by using a fuel cut off switch then the torque converter. from what i understand, the fluids inside of the trans are what actually lubricate the internals. that's why towing in neutral would burn up an aod.

coasting vs Miles / Gal

Reply #3 – July 17, 2014, 09:40:45 PM

First thing is coasting is illegal in most states. Not sure which ones. Second the cooling lines have nothing to do with line pressures. Blocking them would be disastrous. Third you will loose engine breaking that is utilized by de-excelleration. In general a very bad idea, By the way the transmission is not getting enough lubrication in neutral with the drive shaft spinning at highway speeds and the tranny in neutral. Just ask the motor home guys about this. Towing a car behind a camper burns out many trannys because of this. Basically a very bad idea and should not be done. You will loose compression breaking and might loose control of the vehicle. Just some thoughts on the subject. Have a great evening guys

coasting vs Miles / Gal

Reply #4 – July 17, 2014, 10:23:08 PM

Nearly every new car shuts the engine.off at coasts down a certain grade hill. my fiesta (2011) also dis enguages the torque converter on downhill grades and at a traffic light.

coasting vs Miles / Gal

Reply #5 – July 18, 2014, 05:54:25 AM

Many states have laws against coasting so i guess ford builds Fiestas differently to comply to each states laws. But many cars either shut down or disengage at traffic lights ETC to save fuel. Coasting is very dangerous and does not save fuel. Compression breaking is necessary to keep the car under control. Have you ever seen the signs on the roads that tell drivers when going down hill to use a lower gear. If in fact your car actually coasts by design i would be shocked. Can you post the info of your statement? I would like to know for sure if true.

How does the ECM know your car is going down HILL???????????

Hybrids use regeneration breaking to charge there batterys. It accomplishes 2 things Control of the car and recharging the batterys. You need deceleration breaking for proper handling and control.

If memory serves me SAAB had a 2 stroke with a manual transmission that had a freewheeling type tranny of sorts. NOT AN AUTO TRANNY . I think it was because the engine was a 2 stroke not 100%. If memory serves me it was an emission thing. . But as far as a car disengaging to save fuel and designed in to the ECM at highway speeds, I know of none. Please enlighten me if i am wrong. Thank you. And have a great friday

coasting vs Miles / Gal

Reply #6 – July 18, 2014, 09:17:10 AM

Quote from: TOM Renzo;436066

How does the ECM know your car is going down HILL???????????

Sort of unrelated to this thread but I had an experience that relates to Tom's question.

Brand new 2014 Toyota FJ Crusier. Ascending up a long highway hill at 65 mph or thereabouts and I let off the gas removing the load from the transmission at the bottom of the hill just at the beginning of ascension. Every other car I have ever driven would have advanced into a lower ratio gear like OD or something if my gear selector position allowed it. This truck did not. I had enough momentum from going down the previous hill and crossing the river bridge to make it up this hill without having to stay in the accelerator. I only used the gas a little to keep the momentum going at the bottom of the hill and then let off expecting that shift into OD but it didn't happen. In most cars if I know the transmission could hunt back and forth between D and OD, I would just manually keep it in D until I get through that part of the road that can cause the transmission to go back and forth because the car doesn't know I'm on a hill. But I know what's ahead so I may keep it out of OD if there are a series of lights or hills or something that would cause excessive shifting. I had this gear position in the highest though when this happened allowing the truck to use all its gears. But do these new cars know where the hills are due to their increasing black box and GPS technology? Did this truck know I was on an incline? Did it "learn" from previous passes over this portion of the road? Was it a total fluke?

Back to the main topic, my MarkVIII would coast like jcassity mentions when going down a long hill with the transmission properly engaged and everything. It always jumped to 99mpg on the screen. My Cougars though do not coast as freely as the Mark on the same hills and the ones with an mpg reading on the dash do not jump to 99mpg nearly as easily as my MarkVIII did. Many, many times I averaged 29.5 in that MarkVIII. The only Cougar that achieved the same high average was my 87 LS 3.8L back in the 90s. My V8 cars don't get past 24 or so and they don't coast as easily as my V6 LS did.

We have a 2000 Amigo V6 that also doesn't coast down hill. It's RPMs actually increase! It doesn't downshift per se, but it's like some sort of half-gear or something. Higher than OD but lower than 3rd. I've switched to 3rd when that happened to see if the RPMs change again and they do increase again. So it doesn't downshift to 3rd but it does increase its RPMs and put more engine breaking on my coast preventing gravity from increasing my speed. My V12 Jag also doesn't coast like my Mark.

All my Lincolns from the 70s though do coast when going downhill.

Maybe some of these can tell somehow by "reverse load" of sorts. Maybe there is something that senses if the push is coming from the engine versus coming from the driveshaft. Perhaps its a safety thing that if the push is coming from the driveshaft, something prevents a 'sky's-the-limit' increase in speed as high as gravity will take it. Maybe the operation of a properly engaged transmission prevents gravity from exceeding the transmission's ability to properly lubricate itself. The fluid pressure is enough to compete with gravity versus neutral where the fluid pressure is reduced or removed. And perhaps some automatic transmissions by design are better coasters than others.

coasting vs Miles / Gal

Reply #7 – July 18, 2014, 10:59:48 AM

Quote from: jcassity;436010

While I owned an 08 explorer, i noticed when going down hill the transmission would seem to go into a neutral position, this is only an assumption based on what the tac displayed which was close to idle rpm's.

I usually get about 24mpg at highway in my 20th but recently during long road trips i would experiment on each available opportunity of downhill situations and put the trans in N. I am seeing anywhere from 15% to 20% increase in miles per gallon by doing this, however i dont think / feel continuing it would be good on the AOD so i no longer do it.

can we have a discussion on a mod to get this extra mileage on our cars?

I doubt your '08 explorer is going into neutral. It is more likely that it is unlocking the torque converter (this is why your rpms drop) and shutting off fuel flow. Every modern car I've driven does this. Not sure any of our cars has fuel cutoff enabled in the ECU though. I know my '87 3.8L doesn't. It'll only top out at 150-160 mpg on the tripminder, which shows there is still fuel flowing. Fuel shutoff will same some fuel, but not a whole bunch (2-5%).

As far as going coasting in neutral - it shouldn't hurt anything. I believe the transmisison oil pump is driven off the input shaft. As long as the engine is turning, the transmission will be getting oil lubrication. This is much different from a flat towed vehicle behind an RV where the engine isn't turning and isn't delivering any lubrication to the transmission.

Quote from: Cougars 2 go;436068

Sort of unrelated to this thread but I had an experience that relates to Tom's question.

Brand new 2014 Toyota FJ Crusier. Ascending up a long highway hill at 65 mph or thereabouts and I let off the gas removing the load from the transmission at the bottom of the hill just at the beginning of ascension. Every other car I have ever driven would have advanced into a lower ratio gear like OD or something if my gear selector position allowed it. This truck did not. I had enough momentum from going down the previous hill and crossing the river bridge to make it up this hill without having to stay in the accelerator. I only used the gas a little to keep the momentum going at the bottom of the hill and then let off expecting that shift into OD but it didn't happen. In most cars if I know the transmission could hunt back and forth between D and OD, I would just manually keep it in D until I get through that part of the road that can cause the transmission to go back and forth because the car doesn't know I'm on a hill. But I know what's ahead so I may keep it out of OD if there are a series of lights or hills or something that would cause excessive shifting. I had this gear position in the highest though when this happened allowing the truck to use all its gears. But do these new cars know where the hills are due to their increasing black box and GPS technology? Did this truck know I was on an incline? Did it "learn" from previous passes over this portion of the road? Was it a total fluke?

I've got a 2014 4Runner (same powertrain). Toyota has programming to try and reducing hunting on hills. You can read about it here. See page 33.

It doesn't learn (via previous drives [it does learn your particular driving sytle]) or use GPS. I can't quite understand your description, but the transmission can tell if you are going downhill or uphill by sensing actual acceleration vs predicted acceleration. If the throttle is closed and the vehicle is still accelerating, the ECM can deduce that you're going downhill. If you're giving it 90% load in 5th and slowing down, the ECU can deduce you're going uphill. It also acts as a bit of a tow mode because the ECM 'see's the added load from the trailer and will hold gears longer on uphill and downshift earlier on downhills.

coasting vs Miles / Gal

Reply #8 – July 18, 2014, 03:37:51 PM

The mpg display has a lot to do with your map sensor. any type of vacuum leak at all and it will real lower then normal mpg. my 86 cougar i added the trip computer to will read about 125mpg's going down a long hill at about 55mph.

All my digidash tbirds/cougars would hit 99+ mpg basically whenever letting off the gas pedal near freeway speeds. this also changed if a vac leaked popped up, a high idle, or bad timing. advancing the timing effects it quite a bit.

I'm not sure what the fiesta actually uses ti determin how fast to go down hills, but i was driving around the foot hills of a moutain with 5-10% grades on neighborhood roads. down hill it would randomly downshift like crazy and use the engine to prevent you from accelerating. other times it would just. coast down hill like a normal car in neutral. all the 6 speed autos have problems with rolling back on slight hills and not starting off very quickly. been many tsb's about that.

coasting vs Miles / Gal

Reply #9 – July 18, 2014, 04:45:13 PM

The mpg display should correlate directly with actual mpg. Taken from the GUFB document (14-2)

Quote

DATA OUTPUT LINK - TRIPMINDER

The Data Output Link (DOL) provides a communication line between the EEC and the vehicle dashboard computer, Tripminder, for the transfer of fuel consumption information. The fuel flow information sent by the EEC is used for computation of instantaneous and average fuel economy, which is then displayed to the driver.

The Tripminder requires an appropriate integer number of pulses within 100 msec period. Therefore, within each background loop or each 100 msec period, whichever is shorter, the EEC sums the fuel flow and through the injectors output since the summing period started, converts this sum into DOL pulses, and outputs these pulses at a maximum frequency of 500 Hz during the following summation period.

The fuel flow is converted into DOL pulses according to the following equation:

DOL_COUNT = INTEGER (FUEL_SUM * 7804.19 * INJOUT) + DOL_COUNT

The FUEL_SUM is then reduced by the amount converted into DOL_COUNTS (One DOL_COUNT = 1.282E-4 lbm).

where,

[INDENT]DOL_COUNT = Number of pulses to be output beginning in the next summation period. One DOL_COUNT = 1.282E-4 lbm.[/INDENT]

[INDENT]FUEL_SUM = Sum of fuel flow per injector, which was initiated since last summation period. It is updated during the Fuel PW output routine.[/INDENT]

[INDENT]7804.19 = (48000 pulses/gal)/6.15 lbm/gal, pulses/lmb.[/INDENT]

[INDENT]INJOUT = Number of injectors per output port. (See Fuel Strategy)[/INDENT]

[INDENT]FUEL_SUM = FUEL_SUM + LBMF_INJn[/INDENT]

[INDENT]LBMF_INJn = Fuel Flow per injector, calculated from FUELFLOWn (n= 1, 2). (See Fuel Strategy).[/INDENT]

So you've had a vacuum leak or advanced timing that would cause the tripminder to read much different than the actual fuel economy?

coasting vs Miles / Gal

Reply #10 – July 18, 2014, 05:49:59 PM

I'm not sure how important the map sensor or vac pressure is for the actual mpg, but you accidently unplug or break your map sensor line, you will get about 6mpg city and about 11 freeway.

Go advance your timing from 10-14*. My car has more power and was averaging the same mpg as before when set to *14. Decreasing it to 10* brought my average from 22 to 25mpg and a best from 25mpg to 27 or 28mpg according to the trip computer. city driving stayed in the 19-20mpg range by calculating at the pump. The freeway mpg i never got a really good solid run to compare with, but it consistantly stayed in the 25mpg range.

back when i was doing 100-300 miles a day with my old 87 bird with digidash, i tried to tune the timing by the mpg display and compared it with actual mpg calculated at the pump. best mileage was about 15* by the pump, 16-19* by the guage.

My best overall average for a tank was 35mpg by the guage, 33ish by the tank, 100% freeway. a few times i managed over 600 miles to a tank of gas, a few times getting over 650 miles.

coasting vs Miles / Gal

Reply #11 – July 18, 2014, 07:05:54 PM

Quote from: TOM Renzo;436066

How does the ECM know your car is going down HILL???????????

Quote from: JeremyB;436070

... the transmission can tell if you are going downhill or uphill by sensing actual acceleration vs predicted acceleration. If the throttle is closed and the vehicle is still accelerating, the ECM can deduce that you're going downhill. If you're giving it 90% load in 5th and slowing down, the ECU can deduce you're going uphill. It also acts as a bit of a tow mode because the ECM 'see's the added load from the trailer and will hold gears longer on uphill and downshift earlier on downhills.

Brilliant. Thank you. So when this question refers to a newer vehicle, there is a better chance the ECM does know. For Cougars, though, I suppose the ECM doesn't know uphill or downhill.

Yes, I am guilty of run-ons when I don't have the time to go back and refine. But you understood what I was trying to say.

Quote from: Haystack;436079

My best overall average for a tank was 35mpg by the guage, 33ish by the tank, 100% freeway. a few times i managed over 600 miles to a tank of gas, a few times getting over 650 miles.

I achieved over 500 miles many times in my 87 LS V6 on long highway trips. Doing the math using the trip odometer and the gallons usually ended up around 30mpg. Speeds were uh... not 55.

coasting vs Miles / Gal

Reply #12 – July 19, 2014, 12:27:23 AM

If the throttle is closed and you are going down hill if the transmission goes in to neutral as described then what. Even if it knows what good does it do. If it is not doing anything. Sounds like many trannys will be smoked because if this constant de-clutching or going in to coast mode as you call it.

coasting vs Miles / Gal

Reply #13 – July 19, 2014, 03:46:08 AM

The idle is lowered from 800rpm's when the torque converter is loaded to 600rpm's when your in idle.

fuel load increases substancally with rpms, but i doubt 200rpms would make much differance. going with a fuel cutoff switch, or engine off coasting would greatly improve over that.