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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #26  
Old 06-02-2005, 07:45 PM
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cwsqbm cwsqbm is offline
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Quote:
Originally Posted by nv
The blip is this.

There is a continuous and instantaneous calculation of your gas mileage. At a stop the calculation should produce 0 mpg (far right indication) because that is what you are getting. Just before the stop the needle is in transition to that far right position. BMW choose to display infinite mpg at stop (a far left indication) instead of the true 0 mpg. So as you stop the needle swing to the right (as it should) and then back to the left (by design) when stopped.

-Neil
The way I always think about it consider that the gauge wasn't designed to show mpg, but L/100km instead, and just has a different label for U.S. Therefore, when the car stops, you have a divide-by-zero error, so instead its more reasonable then to show 0 L/100km because the car isn't moving.
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  #27  
Old 06-02-2005, 08:22 PM
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Quote:
Originally Posted by icemanjs4
Recently I found myself eyeing the mpg guage a little too often. The results was I found myself driving the BMW like a Camry in order to keep the needle as close to 30 as I could get it. After a week or two I realized I wasn't having as much fun with my car and couldn't figure out why . So finally I decided to perform an experiment with the next two tanks of gas.

The first tank of gas, I always kept the needle close to 30 mpg (within reason). I tried to keep the car in overdrive as much as possible (6 spd manual so I spent a lot of time in 5th and 6th gears). I also used cruise control a lot. It was excruciating!

The 2nd tank of gas I drove without ever looking at the mpg guage. I accelerated hard on the on ramps. I spent more time in 4th on the highway (I even pulled 80 in 3rd a few times - 3rd gear rocks at 5K rpms!). I tried to keep the car within 15 mph of the speed limit, but that was my only sort of restriction.

End result: No difference. I actually got .2 mpg better results on the 2nd tank of gas. The upside is, I had a whole lot more fun in round 2. The bad news is I was getting about 22.2 miles per gallon in a mix of city and highway driving.

Moral of the story? Drive it like you stole it and forget about the gas guage!

Just got back from SF (live in San Diego) last night. I got over 30 mpg in my 330i 6 MT at an average speed of 87 mph. I love my car sometimes. On long drives like that, it's quickly apparent why.
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  #28  
Old 06-03-2005, 12:55 AM
SpeedinBlueBima SpeedinBlueBima is offline
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No one seemed to mention the fact that the car is adaptive, if you drive it agressivly 90% of the time and then pamper it for one tank of gas, its not going to show much better fuel consumption. If you did that for several tanks Im assuming it would be much more noticeable.
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  #29  
Old 06-03-2005, 09:27 AM
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SD and D

After 2 years of owership I started to wonder about the same thing - driving aggressiveness does insignificant effect to MPG. For the most recent tank of gas, I put the gear to sport mode (SD) all the time. I am actually getting ~8% improvement in MPG compare with driving in D mode before. This maybe just the weather has been getting warmer though. It is necessary to try a few more tanks to draw a conclusion. But that's the observation so far!
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  #30  
Old 06-03-2005, 10:50 AM
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Quote:
Originally Posted by yamato
After 2 years of owership I started to wonder about the same thing - driving aggressiveness does insignificant effect to MPG. For the most recent tank of gas, I put the gear to sport mode (SD) all the time. I am actually getting ~8% improvement in MPG compare with driving in D mode before. This maybe just the weather has been getting warmer though. It is necessary to try a few more tanks to draw a conclusion. But that's the observation so far!
You guys are talking automatics. I can see a wide difference in my car with how I drive but I have a 6 speed.
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  #31  
Old 06-03-2005, 12:01 PM
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Quote:
Originally Posted by icemanjs4
Recently I found myself eyeing the mpg guage a little too often. The results was I found myself driving the BMW like a Camry in order to keep the needle as close to 30 as I could get it. After a week or two I realized I wasn't having as much fun with my car and couldn't figure out why . So finally I decided to perform an experiment with the next two tanks of gas.

The first tank of gas, I always kept the needle close to 30 mpg (within reason). I tried to keep the car in overdrive as much as possible (6 spd manual so I spent a lot of time in 5th and 6th gears). I also used cruise control a lot. It was excruciating!

The 2nd tank of gas I drove without ever looking at the mpg guage. I accelerated hard on the on ramps. I spent more time in 4th on the highway (I even pulled 80 in 3rd a few times - 3rd gear rocks at 5K rpms!). I tried to keep the car within 15 mph of the speed limit, but that was my only sort of restriction.

End result: No difference. I actually got .2 mpg better results on the 2nd tank of gas. The upside is, I had a whole lot more fun in round 2. The bad news is I was getting about 22.2 miles per gallon in a mix of city and highway driving.

Moral of the story? Drive it like you stole it and forget about the gas guage!

When I drive for economy, I get 33-34 mpg average. When I drive for fun, I get ~ 20-21 mpg. You either don't know how to drive for economy or don't know how to have fun, bud
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  #32  
Old 06-04-2005, 05:30 PM
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I'm sorry guys, but that MPG guage is just a vacumn gauge. I've had and used vacumn gauges before and this one behaves exactly like all the others. It does NOT actually show instaneous MPG. In fact, it can be grossly inacurate. The needle goes to 'infinity' at rest because that is when manifold vacumn is the greatest. The 'blip' could be any number of things, probably some form of emissions control.
One demonstration of the vacumn guage behavior: on a level road, drive at a constant 40 MPH or so in 5 or 6th (assuming manual). You'll be showing around 50 MPG. Now, slightly press on the accelerator; the vacumn gauge will make a rather drastic dive to the right (low mileage)... much more of a reaction then the actual MPG would change, but very much in keeping with the way a vacumn guage reacts.
By the way, when I'm a little 'careful', I get a average of around 26-27 MPG in my 2004 330CI (6M) with mostly surburban driving (not much stop-and-go, but not much interstate either). When I drive it hard, I drop to around 24 - 25 still not at all bad! On the interstate I get about 33 MPG at 73 - 75 MPH.
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  #33  
Old 06-05-2005, 05:35 PM
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car_for_mom car_for_mom is offline
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Another way to improve my gas mileage (currently around 23.5 mpg), besides proper tire inflation, watching starts, etc: don't let The Oldest Tax Deduction (age 17) drive my car!

Ah, occasionally, the fact that I carried him around for nine months and gave birth to him persuades me to allow him to drive my Bimmer ("Mom, pleeeeease can I drive your car? Pleaaase?" "It shifts so smoothly; it rides so nice!" [yah, well, it's a BMW ])

He actually is very good in my 325i; but for some reason, his foot is more leaden in my car than in his 1991 Nissan 240SX!
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  #34  
Old 06-05-2005, 05:57 PM
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Quote:
Originally Posted by icemanjs4
Recently I found myself eyeing the mpg guage a little too often. The results was I found myself driving the BMW like a Camry in order to keep the needle as close to 30 as I could get it. After a week or two I realized I wasn't having as much fun with my car and couldn't figure out why . So finally I decided to perform an experiment with the next two tanks of gas.

The first tank of gas, I always kept the needle close to 30 mpg (within reason). I tried to keep the car in overdrive as much as possible (6 spd manual so I spent a lot of time in 5th and 6th gears). I also used cruise control a lot. It was excruciating!

The 2nd tank of gas I drove without ever looking at the mpg guage. I accelerated hard on the on ramps. I spent more time in 4th on the highway (I even pulled 80 in 3rd a few times - 3rd gear rocks at 5K rpms!). I tried to keep the car within 15 mph of the speed limit, but that was my only sort of restriction.

End result: No difference. I actually got .2 mpg better results on the 2nd tank of gas. The upside is, I had a whole lot more fun in round 2. The bad news is I was getting about 22.2 miles per gallon in a mix of city and highway driving.

Moral of the story? Drive it like you stole it and forget about the gas guage!
Agreed!
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  #35  
Old 06-05-2005, 08:11 PM
De_UnKnOwN_1 De_UnKnOwN_1 is offline
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Did the SAME thing with my car when i first got it..and every minute of it sucked lol
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  #36  
Old 06-05-2005, 08:18 PM
bluejeansonfire bluejeansonfire is offline
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I've been having the same problem recently.

I've been eyeing the little vaccum gauge too much, I achieved a 29.7 mpg average. Before, I averaged 25.5- hard acceleration all the time, but once cruising speed was reached, even w/ te 25.5 average, I could keep the gas neede over 30. I have found it that the cruise control wastes more gas than my still-as-a-stone foot, I can accelerate to about 15 mph over desired speed, over the course of the next 15-20mins I'll very slowly drop speed to actual speed limit, this is the ultimate in gas savings. I found that to sasify the vaccum gauge, you must treat the car as a boat- attempting to hydroplane at minimal speed: exceed 35mph then you can drop back to 25, but if you just accelerated to 30, you wouldn't be hydroplaning. avoiding stops also improves gas mileage- put car into low gear to slow car, drive in traffic slowly w/out stopping.
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  #37  
Old 06-06-2005, 08:29 AM
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Quote:
Originally Posted by grayghost
I'm sorry guys, but that MPG guage is just a vacumn gauge.
If you take the cluster out, you will see it is fully electronic / electrical. As Andy S. has previously stated, this gauge just uses buffered signals from the engine management computer. It may behave like a vacuum gauge but it isn't one. It only requires two screws to be removed to take out the instument cluster, so you can have a look if you are curious.
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  #38  
Old 06-06-2005, 12:20 PM
dgkfl dgkfl is offline
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Not a vacuum gauge

Not only that: Just watch the gauge as you coast down to a stop with your foot on the clutch. You will see the gauge slowly move over to the right and then to the left. It would not behave this way if it were a vacuum gauge, because the vacuum in such a situation would be constant. The gauge is definitely reflecting both some indication of gasoline flow, AND the speed of the car. At idle (with the clutch in), the engine is burning gasoline at a fixed rate, so as you slow down, your mpg drops down until it hits 0 (which the gauge treats as infinity.).

David
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  #39  
Old 06-06-2005, 07:14 PM
grayghost grayghost is offline
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I have no doubt that the guage is 'electric'.... There is surely a sensor in the manifold that senses the manifold vacumn and this 'electrical' signal (probably digitized) is displayed as MPG. Here's an experiment to back up my position...
- With car in 1st gear on level ground allow car to move at idle speed. Foot off the accelerator. I believe you will see that the needle is almost all the way over toward 50. This is because the car is under a very light load, almost like an unloaded idle, so manifold vacumn is very high. I don't think you're getting 50 MPG in this mode.

I haven't seen any behavior of the needed to suggest anything other than a 'pure' manifold vacume guage (electrical or not) but I've seen a numebr of circumstances where the needle just would not logically be a correct indication of instaneous MPG.
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  #40  
Old 06-08-2005, 08:27 PM
Adventure Rider Adventure Rider is offline
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At first I too thought it was a vacuum guage, and maybe it does have some hook up to vacuum, but there is one time it does not act like a vacuum guage - that is when you are coasting. Today, several times, in bad stop-n-go traffic, I was coasting, out of gear, clutch out, foot off the throttle and as I coasted along the guage registered a reading in the 30-50 MPG range. Stop and it goes over to the left all the way, roll along and it goes back to the right and varies with speed despite the the fact that engine has no load.

Obviously there is something going on there that is not just vacuum.
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  #41  
Old 06-08-2005, 08:39 PM
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Quote:
Originally Posted by cwsqbm
The way I always think about it consider that the gauge wasn't designed to show mpg, but L/100km instead, and just has a different label for U.S. Therefore, when the car stops, you have a divide-by-zero error, so instead its more reasonable then to show 0 L/100km because the car isn't moving.
Agreed. My car is L/100km. The meter is a linear 0 on the left and 20L/100km on the right. When the car isn't moving the display is 0L/100km (or infinite mpg).
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  #42  
Old 06-09-2005, 08:48 AM
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cwsqbm cwsqbm is offline
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Quote:
Originally Posted by grayghost
I have no doubt that the guage is 'electric'.... There is surely a sensor in the manifold that senses the manifold vacumn and this 'electrical' signal (probably digitized) is displayed as MPG. Here's an experiment to back up my position...
- With car in 1st gear on level ground allow car to move at idle speed. Foot off the accelerator. I believe you will see that the needle is almost all the way over toward 50. This is because the car is under a very light load, almost like an unloaded idle, so manifold vacumn is very high. I don't think you're getting 50 MPG in this mode.

I haven't seen any behavior of the needed to suggest anything other than a 'pure' manifold vacume guage (electrical or not) but I've seen a numebr of circumstances where the needle just would not logically be a correct indication of instaneous MPG.
Actually, idling in first gear the neddle is not at 50mpg, but a lmuch ower setting. It is NOT a vacuum gauge. The computer takes speed divided fuel used (which it knows because it controls the fuel injector). As for proof:

Quote:
Originally Posted by dgkfl
Not only that: Just watch the gauge as you coast down to a stop with your foot on the clutch. You will see the gauge slowly move over to the right and then to the left. It would not behave this way if it were a vacuum gauge, because the vacuum in such a situation would be constant. The gauge is definitely reflecting both some indication of gasoline flow, AND the speed of the car. At idle (with the clutch in), the engine is burning gasoline at a fixed rate, so as you slow down, your mpg drops down until it hits 0 (which the gauge treats as infinity.).

David
The reason it swings to infinity when stop is the gauge doesn't work below a certain speed (IIRC, maybe 2mph). As am experiment, stop on the top of hill with car not in gear. Let off the brakes and as you start to go down the hill, you notice that the gauge swings from infinite mileage to a low number (at the cut off speed) before slowly going back up.
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  #43  
Old 06-09-2005, 07:00 PM
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a tad off topic but, when I feed my 5er 94 octane I noticed the 'range' goes up to 450mi-470mi from the normal 350mi on 93. Now I'm not too sure about 92 in CA.

I say just drive like a normal human being and don't worry about how much mpg your going to get out of your driving style because it's probably not $$$ of a difference. 6spd is different, of course go easy on the high revving. Just get up to the speed you need to get yourself up too and cruise from there, we're not racing to every redlight now are we?

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  #44  
Old 08-10-2005, 09:03 AM
sketchy sketchy is offline
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Quote:
Originally Posted by grayghost
I have no doubt that the guage is 'electric'.... There is surely a sensor in the manifold that senses the manifold vacumn and this 'electrical' signal (probably digitized) is displayed as MPG. Here's an experiment to back up my position...
- With car in 1st gear on level ground allow car to move at idle speed. Foot off the accelerator. I believe you will see that the needle is almost all the way over toward 50. This is because the car is under a very light load, almost like an unloaded idle, so manifold vacumn is very high. I don't think you're getting 50 MPG in this mode.

I haven't seen any behavior of the needed to suggest anything other than a 'pure' manifold vacume guage (electrical or not) but I've seen a numebr of circumstances where the needle just would not logically be a correct indication of instaneous MPG.

Not only that, but it does what every other vacum gauge does on a manual transmission, gives a misread when you downshift (changing the vacum at that point, going the opposite way you would expect). Try it, and you will see what I mean. Until I see some hard evidence to suggest otherwise, it's a vacum. - sketchy
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  #45  
Old 08-10-2005, 12:47 PM
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Bob Clevenger Bob Clevenger is offline
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Quote:
Originally Posted by sketchy
Not only that, but it does what every other vacum gauge does on a manual transmission, gives a misread when you downshift (changing the vacum at that point, going the opposite way you would expect). Try it, and you will see what I mean. Until I see some hard evidence to suggest otherwise, it's a vacum. - sketchy
Why can't people accept that the mpg gauge is NOT a simple vacuum gauge?

Please describe this "misread" to which you refer. On my cars that have had a real vacuum gauge attached there was no misread. Open the throttle and the vacuum drops until the RPMs catch up. Release the throttle and the vacuum rises. Go to a higher gear (or start climbing a hill) and the vacuum drops. Crest the top of the hill and the vacuum rises. Upshift and the vacuum drops until RPM's catch up. Downshift and the vacuum rises

Want another hint? Hold a steady mid-range RPM (say 3000) in one of the lower gears (like third) and look at your mpg gauge; note the reading mentally. Then shift up a gear (like to fourth) while holding the same road speed. See what happens. The mpg reading goes UP.

Now under these conditions the manifold vacuum would go DOWN slightly ---like from 22"Hg to 18"Hg. That's just how throttle-controlled IC engines work. Valvetronic engines are a whole different matter because there is no intake manifold vacuum at all --- I wonder how the E90's make their "vacuum" gauge work without any vacuum?

One more test you can do. Get in your car and turn the ignition switch ON, but do not start it. Look at your mpg gauge. It's all the way to the left (inf. mpg) isn't it? That would be maximum vacuum if it were a vacuum gauge. From where is the vacuum coming? The engine is not running. The gauge is powered up, so it should be working.
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  #46  
Old 08-10-2005, 05:14 PM
nv nv is offline
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Quote:
Originally Posted by Bob Clevenger
Why can't people accept that the mpg gauge is NOT a simple vacuum gauge?

You got it right Bob.

It's also fairly accurate. Less than 1 mpg optimistic. I checked my first 20 fill-ups.

-nv
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  #47  
Old 08-11-2005, 06:46 AM
Adventure Rider Adventure Rider is offline
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Quote:
Originally Posted by sketchy
Not only that, but it does what every other vacum gauge does on a manual transmission, gives a misread when you downshift (changing the vacum at that point, going the opposite way you would expect). Try it, and you will see what I mean. Until I see some hard evidence to suggest otherwise, it's a vacum. - sketchy
Go out on a long downhill with no traffic. Stop. Put the trans in neutral. Don't touch the gas pedal. Let off the brake and roll down the hill. Notice that the mileage meter will show better mileage the faster you go.

Vacuum guages don't do that.
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  #48  
Old 08-11-2005, 04:00 PM
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FenPhen FenPhen is offline
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Quote:
Originally Posted by Adventure Rider
Go out on a long downhill with no traffic. Stop. Put the trans in neutral. Don't touch the gas pedal. Let off the brake and roll down the hill. Notice that the mileage meter will show better mileage the faster you go.

Vacuum guages don't do that.
I have no idea how a vacuum gauge works or what it measures (air going to the engine?). However, I do know that with the computer's "cons" calculator, if you reset to "----", then move a little bit to register a value, the mileage will drop when you sit at idle. That seems to me like it's measuring real fuel consumption.

Also, the service indicator is based on fuel consumption (something like 667 gallons for an MT car). Given that, I'd assume the car is actually measuring fuel sent to the engine and dividing by rolling distance.
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  #49  
Old 08-11-2005, 04:21 PM
pony_trekker pony_trekker is offline
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Quote:
Originally Posted by BBBMW
I have been driving my 02 325Ci for a year now and can't believe how good the gas mileage is. This is the first vehicle that I can drive from Edmonton to Calgary which is about 650 km's (400 miles) on a tank of gas. I usually cruise at 75 mph and notice an extreme difference from my old Acura. It makes having to run premium gasoline a little more tolerable.
These engines are GREAT on the highway (I averaged 32 on a highway trip NY-Boston) but not so great in sto and go stop and start (17-18mpg). I generally drive in Sport verry verrrrry agressively.

In fact I left Ny with barely over a 1/2 tank. By the time I got to MA, it didn't even see the needle move.

Last edited by pony_trekker; 08-11-2005 at 04:24 PM.
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  #50  
Old 08-11-2005, 09:27 PM
Adventure Rider Adventure Rider is offline
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Quote:
Originally Posted by FenPhen
I have no idea how a vacuum gauge works or what it measures (air going to the engine?). However, I do know that with the computer's "cons" calculator, if you reset to "----", then move a little bit to register a value, the mileage will drop when you sit at idle. That seems to me like it's measuring real fuel consumption.

Also, the service indicator is based on fuel consumption (something like 667 gallons for an MT car). Given that, I'd assume the car is actually measuring fuel sent to the engine and dividing by rolling distance.
Exactly. The measures fuel consumed for the digital MPG guage, why can't it do the same to the analog guage?

It is not a vacuum guage, although much of the time it can seem that it is acting like one. A vacuum guage won't change with speed while rolling down a hill with the car in neutral - it would stay steady.
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