downshifting to achieve fuel cut

[omgwtfbyobbq]

Since every autotragic trans is different, different shift patterns may result in different wear. If a specific component will wear out from normal use before another component will from the different use, then it doesn't matter much anyway. Kinda like starters IMO. Normal starting won't put much wear on them and they're usually good for tens/hundreds of thousands of starts. What will kill them is fairly quickly is undervolting/overheating.

[GasSavers_James]

The van doesnt have an o/d button or a 3rd gear, just drive and second...so I shift to 2nd when i am going down hills and need to slow down anyway. I don't do it every time i am coming to a stop. So far I have driven it 6K with no problems. the van has 142 k, and a front end destroyed by deer incident, so i am not too worried about destroying the tranny. he is about to buy a new van. The other shop van is the v6 model with the same tranny, and it only has 114k and already has tranny issues. you have to rev the engine to 4000 to get it to shift into 2nd. great for in town gas mpg. so i figure this 4 cyl model is doing pretty well with 141k on it.

[bzipitidoo]

Last year for a vacation, I drove around Colorado in a minivan with an automatic. I learned that the automatic doesn't know best. Found out the one I was driving would not shift down soon enough for mountain climbs.

One thing you can do with an automatic but not a manual is hold the gas pedal steady while shifting gears. While going up those steep slopes, I experimented with shifting while holding the gas pedal in the same position. If I shifted down, and as a result the van sped up, then I figured the lower gear was the more economical choice. If it slowed down when I shifted down, then the higher gear was better. Got some really killer FE on some of those slopes. Seems having slopes to work with is sort of like pulse and glide. Of course you get terrible FE going uphill and awesome FE going downhill. The overall average worked out to more than I was getting on the flats.

I was surprised to see that gentler slopes can have a large effect too. There's a gradual steady rise when crossing the high plains on the way to the mountains, and on the western side where the rise is a little faster, this apparently made a noticeable dent in FE. On the way back, I was seeing about 20% better FE.

[kamesama980]

Originally Posted by bzipitidoo

Last year for a vacation, I drove around Colorado in a minivan with an automatic. I learned that the automatic doesn't know best. Found out the one I was driving would not shift down soon enough for mountain climbs.

for accelerating, auto know best 99% of the time. for downshifting, it can only react to your input and guess as to what's happening. thus is slow and stupid. my toyota cressida has a very good shift pattern and reacted quickly (relatively speaking). I drove a dodge caravan for a business trip and I had to take it to 1/2 throttle or more for a full second before it'd downshift from OD.

Originally Posted by bzipitidoo

I was surprised to see that gentler slopes can have a large effect too. There's a gradual steady rise when crossing the high plains on the way to the mountains, and on the western side where the rise is a little faster, this apparently made a noticeable dent in FE. On the way back, I was seeing about 20% better FE.

I have data to back this up as well. I've driven chicago-NY and back half a dozen times in a couple different cars and EVERY trip both directions regardless of the car saw 5-8 mpg gain through PA/NJ mountains.

[GeneW]

Originally Posted by James

do you guys with autos do this? I just started a job driving a chrysler 4cyl with the automatic, delivering flowers. i have been downshifting under situations where i need to slow down anyway to 2nd to achieve the fuel cut. I became aware of this driving a jeep grand cherokee down a mountain in vermont. when i clicked the o/d off mpg jumped up to 99, and when i put it back in o/d, it went down to 45. this is with foot off the gas. so i figure when you dont want momentum its better to encourage the fuel cut. I do this with my vx too, going into different gears depending on how much i want to slow down. I figure the chrysler minivans are built the same as the jeep 4.0 l 6 cyl with auto, in that they fuel cut only above a certain rpm. In fact in the minivan you can feel it i think. it seems to fuel cut above 50 mph no problem, but that is not really that big of a help because aero drag slows you down so quickly that the time spent in fuel cut is short. but on long city decents, you can downshift to 2nd and keep fuel cut for a long time and save the brakes!
anyone else do this? Maybe it creates a little more wear on the tranny, but with this van, it doesnt matter, it will only be on the road another 6 months or so.

I had two trannies rebuilt by some guy who only does US models and has an appointment list. Sharp as a tack.

His suggestions were that downshifting is "harmless" going down hills and very beneficial going up hills. He claimed that leaving the tranny in high gear going up hill "superheats" the torque converter. Oddly enough he said that going in reverse is "tough" of all on US made units. Going backwards in hurry with a cold transmission is toughest of all on them.

Where you might see an issue is that engine breaking could over rev the motor.

I am not sure about Deceleration Fuel Cutoff points for Chrysler products. I know for my Caprice, my last US made car, that DFCO is out of the question. The THD will not take it.

Torque clutch lockups vary. My Caprice has one, usually it engages around 47mph to 52mpg. I would not try to make the lockup engage outside of ECU control, though sometimes I'd disable it if it began "hunting".

Hunting is neat - the engine's ECM will try to find the best solution, depending upon load (engine vacuum), speed, TPS readings and other factors. At "borderline" states the ECU will switch the lock up on and off, almost in oscillation. Probably because the torque converter lockup presented a new set of conditions which were satisfied with its release. This oscillation was called "hunting".

The crude ECM probably is the cause of this problem, it lacked the asspower to calculate a nice band of values, such that the car would run either in or out of lockup without oscillation. However I'm speculating.

Ultimately, given tolerances on mechanical and electronic parts and how people drive differently you're confronted with a "cut and paste" situation. You'll have to experiment and see what happens to your FE.

I agree with one poster who claimed that Chrysler minivan trannies are not reliable. I've often heard that they're tranny eaters. Please be careful.

Gene

[aych]

manual shifting and turning od on/off or even shifting to N and D is fine by my terms. I'm driving an 88 toyota camry with 300k on it. still the same tranny, been doing all this shifting for the last 20 years and the only thing i do to the tranny is a fluid change once in a while.. not even a flush. just factory specs =)

[theholycow]

I agree with the ok-to-shift crowd, as far as GM (and probably Ford) vehicles are concerned. GM transmissions are happy and healthy under any treatment I give them.

However, DFCO is tough to get in my 2002 model with the 5.3 V8. I have to be off the gas pedal and higher than 1500rpm for more than 6 seconds before it cuts the fuel. It will then stay in fuel cut down to ~1100rpm.

[GasSavers_RoadWarrior]

Originally Posted by GeneW

I had two trannies rebuilt by some guy who only does US models and has an appointment list. Sharp as a tack.

His suggestions were that downshifting is "harmless" going down hills and very beneficial going up hills. He claimed that leaving the tranny in high gear going up hill "superheats" the torque converter. Oddly enough he said that going in reverse is "tough" of all on US made units. Going backwards in hurry with a cold transmission is toughest of all on them.

Where you might see an issue is that engine breaking could over rev the motor.

I am not sure about Deceleration Fuel Cutoff points for Chrysler products. I know for my Caprice, my last US made car, that DFCO is out of the question. The THD will not take it.

Torque clutch lockups vary. My Caprice has one, usually it engages around 47mph to 52mpg. I would not try to make the lockup engage outside of ECU control, though sometimes I'd disable it if it began "hunting".

Hunting is neat - the engine's ECM will try to find the best solution, depending upon load (engine vacuum), speed, TPS readings and other factors. At "borderline" states the ECU will switch the lock up on and off, almost in oscillation. Probably because the torque converter lockup presented a new set of conditions which were satisfied with its release. This oscillation was called "hunting".

The crude ECM probably is the cause of this problem, it lacked the asspower to calculate a nice band of values, such that the car would run either in or out of lockup without oscillation. However I'm speculating.

Ultimately, given tolerances on mechanical and electronic parts and how people drive differently you're confronted with a "cut and paste" situation. You'll have to experiment and see what happens to your FE.

I agree with one poster who claimed that Chrysler minivan trannies are not reliable. I've often heard that they're tranny eaters. Please be careful.

Gene

I've read both my voyager and escort owners manuals and both of them suggest that you might want to shift down going up steep hill and for engine braking, particularly if towing or heavily loaded. Yes, slogging it will burn your fluid and your torque convertor. Read some of those towing forums sometime and you'll see some eejut telling people they can't possibly tow a popup with a minivan or a subaru, coz he had this big truck and burned up the tranny going through the rockies. Dumbass likely left it in top or OD and tried to slog it up.

#1 priority for not killing auto trannies, is avoid heat. This means never to let the TC thrash, and also to keep on top of band adjustments etc, and if possible tighten up the shifts, thin old fluid for example will let the linings grind and grind before they engage. Shift kits for severe duty service lengthen the life of the tranny by tightening up the shifts. The firmer it shifts the better, forget about "smooth as butter". Do this experiment if you disbelieve me, flip a bicycle upside down and spin a wheel, using your thumb on the tire, bring it smoothly and slowly to a stop. Burn and grate your thumb? I expect so. Now spin it up to about the same speed and jab your thumb into it hard... hey now, that hurt a lot less didn't it?

It's true about reverse also, this is most often seen on modified trannies with boosted line pressure, the reverse band strut or other parts in that linkage will break if you pound it into reverse and mash the gas. I have a modification on my valve body to ameliorate this, and keep line pressure in reverse low.

The hunting problem is what overcooks many trannies, it's one of the major issues with the Chrysler Utradrive 4 speed models, that and improper fluid. Also kills Windstar trannies. The tranny computer is trying to modulate the lockup and/or shift smoothly and if you're driving at the transition point, which is quite common in fast city traffic, you are effectively driving along with it half applied between two gears, grinding away the linings, burning the fluid, melting solenoid pack plastics and running up a $$$ tranny bill. Chrysler modified the programming in '98 to avoid this (Stock in 99 MY up) . Anything flashed with the new code and kept in fresh chrysler ATF +4 fluid should live to a ripe old age. So anyway, those particular trannies, are actually liable to live longer if you use your ample intelligence to override the programming and shift according to load and traffic rather than just letting it "do it's thing" and self immolate.

___ ___ ___ ___ ___ ___

Just discovered that Ford was having a problem with the DFCO in some models in the 90s, notably the Escort, so it doesn't actually cut off fuel completely, but it does lean it back a lot. Goes real lean. I guess there is some issue with fuel vapor remaining in the ports or something, because completely cutting fuel completely on decel is meant to make an awful racket POP-POPOPOP-POP like some old carbed cars when you shut the throttle suddenly. So apparently they have to put "just enough" fuel in to stop this. Strangely this is reported as around 25-30:1 mixture, which sounds lean enough that it would cause that problem rather than stop it. But anyway, practically cuts fuel consumption in half, so still should be beneficial and should make for less engine braking so longer glides possible.

Possibly theholycow's truck has a similar problem but a different strategy and it waits six seconds while slowly cutting back fuel to make sure none is puddled in the intakes before cutting completely.

[theholycow]

Originally Posted by RoadWarrior

I've read both my voyager and escort owners manuals and both of them suggest that you might want to shift down going up steep hill and for engine braking, particularly if towing or heavily loaded.

I suspect that most manuals agree. I know I've seen it in other manuals.

The firmer it shifts the better, forget about "smooth as butter". Do this experiment if you disbelieve me[...]

Would the same be true for clutch operation with a manual transmission? When I'm shifting at speed (obviously, from a stop this would differ) is it better for the clutch if I accept the shock? I've figured it probably is, and when I'm alone I often accept a kick in the pants as I hurry the clutch between gears (and therefore save a tiny amount of gas too).

Possibly theholycow's truck has a similar problem but a different strategy and it waits six seconds while slowly cutting back fuel to make sure none is puddled in the intakes before cutting completely.

Good thought. I'll have to watch and see if it's slowly cutting back during the delay or dropping off sharply after the delay.

[GasSavers_RoadWarrior]

Originally Posted by theholycow

Would the same be true for clutch operation with a manual transmission? When I'm shifting at speed (obviously, from a stop this would differ) is it better for the clutch if I accept the shock? I've figured it probably is, and when I'm alone I often accept a kick in the pants as I hurry the clutch between gears (and therefore save a tiny amount of gas too).

It should be almost the same, but remember that autos do have a bit of a buffer to driveline shocks in the torque convertor, so try to rev match within a few hundred RPM to avoid undue stress. Remember also that setting off is the most stressful on the driveline and letting the clutch come in hard from a dead stop won't do your tires, engine mounts, CV joints, etc much good. While moving though, letting it grab harder should be good unless you are doing it between 6000 rpm at the top of one gear and 2000 at the bottom of another, which could cause undue stress, letting revs drop a bit before letting it in hard should be okay.