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18 replies to this topic

#1 OFFLINE   thecarp

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Posted 25 May 2009 - 12:13 PM

I noticed my awd flex when coasting from about 40 mph will hold back and then free wheel as it downshifts through the gears. I have never had this happen in any vehicle I ever owned. Does anyone else experience this? This is the first six speed transmission I have had but all transmissions in the past did not have a rear pump that would hold back the engine.

#2 OFFLINE   matslapper

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Posted 26 May 2009 - 03:50 PM

I have noticed a sluggish "drag", like a down shift when I'm in cruise control and the car is headding down a slight grade. It dosen't seem harsh or alarming just kind of uncomfortable. Anyone else notice this abnormality?
T

#3 OFFLINE   jrmgkia

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Posted 28 May 2009 - 10:13 AM

I have noticed a sluggish "drag", like a down shift when I'm in cruise control and the car is headding down a slight grade. It dosen't seem harsh or alarming just kind of uncomfortable. Anyone else notice this abnormality?
T

Yes the cruise control does not have the ability to apply the brakes to slow the vehicle down a decent so what it does is downshift the tranny to rev up the engine and increase compression braking. I personally wish the cruise would allow the Flex to gain speed on a downhill (i.e freewheel) but others don't like that so Ford designed the Flex to maintain the same speed no matter whether or not the Flex is going downhill or uphill.

#4 OFFLINE   MDGT

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Posted 28 May 2009 - 11:42 AM

I noticed my awd flex when coasting from about 40 mph will hold back and then free wheel as it downshifts through the gears. I have never had this happen in any vehicle I ever owned. Does anyone else experience this? This is the first six speed transmission I have had but all transmissions in the past did not have a rear pump that would hold back the engine.


Yes, I have noticed exactly what you are stating above. You can feel more resistance/downshifting when you are coasting to come to a stop or just slow down(without hitting brakes). I actually think it's to help the car get ready for you to accelerate again so that when you do hit the gas again, it's already in the correct gear.

#5 OFFLINE   rmc523

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Posted 28 May 2009 - 12:07 PM

I personally wish the cruise would allow the Flex to gain speed on a downhill (i.e freewheel) but others don't like that so Ford designed the Flex to maintain the same speed no matter whether or not the Flex is going downhill or uphill.


I wish it'd do that too, and then have it coast back to the set speed when you get on flat ground. Oh well....

#6 OFFLINE   bradwintermute@yahoo.com

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Posted 07 July 2009 - 06:59 PM

Mine does the same thing - not using cruise. When I let off the gas the transmission stays in gear an doesn't let the vehicle coast. I did a test vs my 2005 F150 on a slight grade near my home. At the top of the hill I let off the gas in my F150 at 40 MPH and was doing 46 MPH at the bottom of the hill. The same test in the FLEX resulted in 40 MPH at the top and 28 MPH at the bottom, when I re-did the FLEX test and manually shifted into Neutral at the top (40 MPH) and the FLEX hit 46 at the bottom of the hill. This seems like it will rob fuel economy by limited coasting abilty. I've asked the dealer to take a look to be sure it is right, but it really seems like that down-hill assist is engaged and it shouldn't be.

#7 OFFLINE   itguy08

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Posted 08 July 2009 - 06:02 PM

Mine does the same thing - not using cruise. When I let off the gas the transmission stays in gear an doesn't let the vehicle coast. I did a test vs my 2005 F150 on a slight grade near my home. At the top of the hill I let off the gas in my F150 at 40 MPH and was doing 46 MPH at the bottom of the hill. The same test in the FLEX resulted in 40 MPH at the top and 28 MPH at the bottom, when I re-did the FLEX test and manually shifted into Neutral at the top (40 MPH) and the FLEX hit 46 at the bottom of the hill. This seems like it will rob fuel economy by limited coasting abilty. I've asked the dealer to take a look to be sure it is right, but it really seems like that down-hill assist is engaged and it shouldn't be.


It's right. IIRC the Flex uses aggressive deceleration fuel cutoff. Basically when you coast it stops pumping fuel into the engine to maximize fuel economy. So you get the feeling of engine braking and better fuel economy.

Here you go - right from the horse's mouth:
http://media.ford.co...rticle_id=28869

#8 OFFLINE   bradwintermute@yahoo.com

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Posted 08 July 2009 - 07:00 PM

It's right. IIRC the Flex uses aggressive deceleration fuel cutoff. Basically when you coast it stops pumping fuel into the engine to maximize fuel economy. So you get the feeling of engine braking and better fuel economy.

Here you go - right from the horse's mouth:
http://media.ford.co...rticle_id=28869


WOW!, Ford really needs to teach their dealers about this -- especially if the Flex is the first vehicle to have it. Here I think there's a major problem and it's just normal. Although now that it doesnt coast as far as an vehicle from a few years ago I wonder if the fuel savings is really that much. Anyway, thanks for the info.

#9 OFFLINE   itguy08

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Posted 09 July 2009 - 02:42 AM

WOW!, Ford really needs to teach their dealers about this -- especially if the Flex is the first vehicle to have it. Here I think there's a major problem and it's just normal. Although now that it doesnt coast as far as an vehicle from a few years ago I wonder if the fuel savings is really that much. Anyway, thanks for the info.


No problem at all. I'm surprised that the service dept. knew nothing about it.

#10 OFFLINE   baggs32

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Posted 09 July 2009 - 08:27 AM

Although now that it doesnt coast as far as an vehicle from a few years ago I wonder if the fuel savings is really that much. Anyway, thanks for the info.


I'm with you there. There's a long, roughly 2 miles long, winding hill I drive on every day on my way to work. In any other car I've owned I could get it up to 35+ MPH and drift from that point all the way to the end without hitting the gas at all. In the Flex I'm hitting the gas almost all the time because of the stupid engine braking that slows the car down quite a bit. This isn't as noticeable on steeper hills but on this particular run, which is not steep at all, there's a good bid of slowing down going on. I've been resorting to throwing it in neutral to do the gas-less drift then popping it back into drive when needed at the end.

Situations like this are few and far between I'd wager. But I don't see how I'm saving any gas when I have to keep my foot on it going down hill in a Flex whereas any other car will just keep on going.

#11 OFFLINE   Waldo

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Posted 09 July 2009 - 10:41 AM

I'm with you there. There's a long, roughly 2 miles long, winding hill I drive on every day on my way to work. In any other car I've owned I could get it up to 35+ MPH and drift from that point all the way to the end without hitting the gas at all. In the Flex I'm hitting the gas almost all the time because of the stupid engine braking that slows the car down quite a bit. This isn't as noticeable on steeper hills but on this particular run, which is not steep at all, there's a good bid of slowing down going on. I've been resorting to throwing it in neutral to do the gas-less drift then popping it back into drive when needed at the end.

Situations like this are few and far between I'd wager. But I don't see how I'm saving any gas when I have to keep my foot on it going down hill in a Flex whereas any other car will just keep on going.


But you're assuming that the gas pedal relates to the amount of fuel injected into the engine. It doesn't. The computer matches your throttle input to the amount of torque you need to maintain your speed or accelerate. So just because you are pushing the gas, doesn't mean that you are actually burning more gas.

When you have your foot off the gas, the computer assumes you want to slow down, so it cuts off all fuel and manages the engine braking. But if you're going downhill with your foot slightly on the gas, it's putting in just enough fuel to prevent engine braking and/or allowing the transmission to upshift. When you throw it in neutral, the computer has to use enough fuel to keep the engine idling.

So coasting in neutral guarantees you will be burning fuel the entire time. Letting off the gas completely burns zero fuel for some time, but then more fuel a bit later on. Pushing the gas just enough to maintain your speed down the hill lets the computer figure out what's the most efficient way. Coasting in neutral is NEVER the most fuel efficient way to go downhill unless you turn the engine off.

#12 OFFLINE   baggs32

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Posted 10 July 2009 - 09:29 AM

But you're assuming that the gas pedal relates to the amount of fuel injected into the engine. It doesn't. The computer matches your throttle input to the amount of torque you need to maintain your speed or accelerate. So just because you are pushing the gas, doesn't mean that you are actually burning more gas.


Right, but since the tach moves higher when I'm pushing the gas pedal you can bet I'm burning more gas. More RPMs = more gas burned. That's not something that should happen when going down a slight grade no matter how long it is. It's not an issue on a steep hill because speed builds too fast.

When you have your foot off the gas, the computer assumes you want to slow down, so it cuts off all fuel and manages the engine braking. But if you're going downhill with your foot slightly on the gas, it's putting in just enough fuel to prevent engine braking and/or allowing the transmission to upshift. When you throw it in neutral, the computer has to use enough fuel to keep the engine idling.


Right again. However, like I said above, it has to be given enough gas to actually accelerate due to the deceleration the fuel shut-off caused. That's using more gas than idling in neutral ever will.

So coasting in neutral guarantees you will be burning fuel the entire time. Letting off the gas completely burns zero fuel for some time, but then more fuel a bit later on. Pushing the gas just enough to maintain your speed down the hill lets the computer figure out what's the most efficient way. Coasting in neutral is NEVER the most fuel efficient way to go downhill unless you turn the engine off.


Again, coasting in neutral is more efficient in this case because my foot is constantly on the gas. In neutral some speed scrubs off in the bends but picks back up quickly once out of the bend. In Drive the same speed scrubs off but I have to push the gas pedal in even more to gain the speed back.

What you have to realize, and you couldn't have because I didn't mention it before, is that the RPMs are higher than they would be in Neutral at idle when in Drive. Because I'm on the gas the whole time at a higher RPM than neutral, and therefore the gas is rarely ever shut off to save fuel, it's not saving me any gas on this one particular stretch, but rather it's wasting gas when in Drive. Does it save me gas the other 70% of my drive? Most likely. Just not on this one stretch of road. It's a good idea that Ford had here but I do feel it still needs a bit of work which I'm sure they are aware of already. When this lease is up I'll be interested to see what it's like in my next Ford.

#13 OFFLINE   Waldo

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Posted 10 July 2009 - 11:55 AM

RPM has nothing to do with the amount of fuel being burned. When going downhill, the engine is being spun by the momentum of the vehicle. On a manual trans car, you can downshift to 2nd gear and spin the engine at 7000rpm without burning any fuel.

Engine braking is caused by the resistance of the engine trying to suck air past the throttle plate. If you open the throttle, there will be less resistance so you will get less engine braking. What you are doing when you push the gas pedal while going downhill is opening the throttle, which reduces the engine braking. But in most cases, the computer realizes what is happening and will keep the fuel turned off. Back in the days of carburetors, opening the throttle would automatically add more fuel, but not on today's computer controlled electronic throttles.

Or think about it this way, if you're burning fuel, then you are creating torque from the engine. If you are in drive and creating torque from the engine, then that torque will be passed on to the tires and it will be used to accelerate the vehicle. This will be added to the acceleration already given to the vehicle by the hill. So if you really were using fuel with your foot on the gas and in drive, then you would pick up more speed than just coasting in neutral. But as you've stated, this is not the case, thus you must not be burning fuel, it's just not possible.

#14 OFFLINE   Flagstaff

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Posted 10 July 2009 - 02:33 PM

Right, but since the tach moves higher when I'm pushing the gas pedal you can bet I'm burning more gas. More RPMs = more gas burned. That's not something that should happen when going down a slight grade no matter how long it is. It's not an issue on a steep hill because speed builds too fast.



Right again. However, like I said above, it has to be given enough gas to actually accelerate due to the deceleration the fuel shut-off caused. That's using more gas than idling in neutral ever will.



Again, coasting in neutral is more efficient in this case because my foot is constantly on the gas. In neutral some speed scrubs off in the bends but picks back up quickly once out of the bend. In Drive the same speed scrubs off but I have to push the gas pedal in even more to gain the speed back.

What you have to realize, and you couldn't have because I didn't mention it before, is that the RPMs are higher than they would be in Neutral at idle when in Drive. Because I'm on the gas the whole time at a higher RPM than neutral, and therefore the gas is rarely ever shut off to save fuel, it's not saving me any gas on this one particular stretch, but rather it's wasting gas when in Drive. Does it save me gas the other 70% of my drive? Most likely. Just not on this one stretch of road. It's a good idea that Ford had here but I do feel it still needs a bit of work which I'm sure they are aware of already. When this lease is up I'll be interested to see what it's like in my next Ford.



Wouldn't the problem be solved by using cruise control at the speed you want to maintain? The car's computer would feed in just enough gas to keep you at the right speed. I suppose no good if you need to maintain a speed lower than the CC can handle. I have a similar hill (but shorter) that I coast down in neutral (2005 Freestyle CVT) and I'm fairly sure it save gas vs. leaving the car in drive and riding the brake. Completely different transmission, of course.

#15 OFFLINE   Waldo

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Posted 10 July 2009 - 04:48 PM

I have a similar hill (but shorter) that I coast down in neutral (2005 Freestyle CVT) and I'm fairly sure it save gas vs. leaving the car in drive and riding the brake. Completely different transmission, of course.


Doesn't matter what kind of transmission, unless you have a carburetor, coasting in neutral will always use more fuel than maintaining your speed in drive. Computers (and the engineers who program them) are pretty smart. I had a friend who worked on GM fuel injection in the mid-80s, and even then they were shutting off the fuel when coasting in drive.

Edited by Waldo, 10 July 2009 - 04:48 PM.


#16 OFFLINE   baggs32

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Posted 13 July 2009 - 09:00 AM

RPM has nothing to do with the amount of fuel being burned. When going downhill, the engine is being spun by the momentum of the vehicle. On a manual trans car, you can downshift to 2nd gear and spin the engine at 7000rpm without burning any fuel.


In this case it does. I monitored the tach this morning on the way in to give you the full details. It boils down to this:

Engine RPM coasting 35-40 MPH in Neutral - ~1100 RPM
Engine RPM coasting in Drive after gas is shut off and compression braking is in effect slowing the vehicle down - ~900 RPM
Engine RPM while in Drive and depressing the gas pedal to maintain 35-40 RPM - 1500+ RPM (1500 was the lowest I read but honestly couldn't stare at the tach the whole time)

So you can see where this gas shut off feature can save you some gas. However I still stand by by statement that it actually forces you to use more gas on certain types of terrain because I need to feed the engine enough gas to keep my speed while going downhill. Not a little gas here and there, but rather a steady flow to hold 1500 RPMs or more. There is no way keeping it in Neutral at a steady 1100 RPM is using more gas. The onboard fuel econ meter proves my point too. Every time I hit the gas to get back up to speed it dropped significantly.

I know how smart the computers in cars are these days but I'm also a programmer by trade and the engine management algorithms are controlled by handwritten software. It is very, very difficult to account for every real world scenario when writing code for a large audience and I wouldn't be surprised to see this anomoly fixed in PCM version 1.1 (made that number up). If, as you state below, it's as simple as opening the throttle plate a little to reduce the engine braking without turning the fuel on, then it should be easy for them to fix.

Engine braking is caused by the resistance of the engine trying to suck air past the throttle plate. If you open the throttle, there will be less resistance so you will get less engine braking. What you are doing when you push the gas pedal while going downhill is opening the throttle, which reduces the engine braking. But in most cases, the computer realizes what is happening and will keep the fuel turned off. Back in the days of carburetors, opening the throttle would automatically add more fuel, but not on today's computer controlled electronic throttles.


Well put. But the problem with my experience is that the engine spools up and you can feel the Flex being pulled by the engine in direct relation to the input of my right foot. What you are suggesting will cause a very gradual increase in speed and give you the sensation that the vehicle is accelerating down a slight hill in neutral. I assure you that is not the sensation I'm feeling when I hit the gas on this stretch. I'll have to try giving it a little less gas and see what happens. You may be on to something here. Someone else also mentioned using CC on this stretch which probably does behave exactly as you describe.

Or think about it this way, if you're burning fuel, then you are creating torque from the engine. If you are in drive and creating torque from the engine, then that torque will be passed on to the tires and it will be used to accelerate the vehicle. This will be added to the acceleration already given to the vehicle by the hill. So if you really were using fuel with your foot on the gas and in drive, then you would pick up more speed than just coasting in neutral. But as you've stated, this is not the case, thus you must not be burning fuel, it's just not possible.


Again, very logical and well put. However the fuel econ meter says otherwise. I suppose it too could have a programming bug in that it's reading the wrong signals at the wrong times in some cases. I'll experiment some more. I think what you're saying makes sense but I don't think it's the case 100% of the time but probably is most of the time.

#17 OFFLINE   Waldo

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Posted 13 July 2009 - 12:42 PM

Again, very logical and well put. However the fuel econ meter says otherwise.


I don't know where the fuel economy meter gets its input for fuel burned, but taking it from the duty cycle of the injectors is only one way to do it. It might just take throttle position compared to distance traveled and infer that a certain throttle position corresponds to a certain amount of fuel used. Over time this would average out, but in this particular scenario it wouldn't.

The problem I have is I live in the flatest piece of earth in the entire world, so I can't go out and try it myself!

#18 OFFLINE   baggs32

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Posted 14 July 2009 - 08:22 AM

I don't know where the fuel economy meter gets its input for fuel burned, but taking it from the duty cycle of the injectors is only one way to do it. It might just take throttle position compared to distance traveled and infer that a certain throttle position corresponds to a certain amount of fuel used. Over time this would average out, but in this particular scenario it wouldn't.


I did some more experimenting yesterday and this morning using the fuel econ meter again. I found that if I depress the gas pedal ever so slightly while the compression braking is in effect (which means the gas is off in the cylinders too) I did feel the sensation of coasting in neutral and the fuel econ meter did not budge. The tach moved up a little because the Flex was accelerating a little but there was no indication that gas was being used. So I think your theory above might hold water in this case. Now there were times when I hit a slight incline, or possibly a level stretch, where I would have to push the go pedal in a little more to maintain speed. In those cases the fuel meter did drop a good bit and the RPMs did increase more than in the previous example.

I'm now convinced that there is a very fine line associated with how far you can push the gas pedal in before those injectors kick back on. During this morning's run I was able to better manage the throttle and I think I kept the gas off more often than not using your suggestion of opening the throttle plate a little to reduce the compression braking. I'll keep playing with it and report any findings back to this thread.

The problem I have is I live in the flatest piece of earth in the entire world, so I can't go out and try it myself!


Well, there are little to no flat surfaces here so my problem is I'll be obsessed with trying it all the time now!

#19 OFFLINE   eosBlue

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Posted 27 May 2010 - 08:31 AM

I think this "downshifting" is probably similar in all "auto stick cars". I have a VW Eos with a 6 speed auto stick tranny and it does the same thing. When I let off on the gas, I can feel the compression, especially at lower speeds (less than 25 MPH). I like this feature, but I HATE downshifting when coming down a hill with cruise control engaged. To be truthful, I don't know if my VW Eos does this, but my Jeep Commander sure does and it pisses me off when I have it set a 60-70 MPH and come to a hill where the car start to roll. When the speed increases a few MPH, the damn thing starts downshifting to try to maintain the speed. That's when I then kick off the cruise control.

And YES, I understand why it does this. I'm very interested in getting a Flex to replace the Jeep and am sad to see that this problem will continue if I carry through with the purchase.






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