Clutch replaced, feels like different ratios

[jax4bangin]

That's why... You can't believe the "instant" mpg calculations, my uncle has a new Cadillac that has that feature and whenever he takes off it claims he gets 1 mpg... Once he gets on the highway it can go up to 40mpg (from a v8 in a big heavy car)

the instant mpg calculator is most likely accurate.. it all depends on throttle position.. say ur uncle is maintaining 70 mph on the freeway, its probably reading around 17-22 mpg, but if he eases off the throttle and starts to decelerate, the comp will read less fuel being sent but still high a mph. there fore it can calculate 40+ mpg at the moment of time.

my moms mini cooper has the instant mpg app. and wen ever u let off the gas completely, it shoots up to 99.9 mpg(which is the highest it reads) for the moment given.

open minded thinking, some of u guys shudd try it sometimes.

as for the op, 35 in 5th is prolly only a lil over idle but shoot if ur not hardly pressin the gas pedal then ur not bogging it.. its simply running an easy task of keeping a small ass truck at 35 mph. prolly only takes 3-4 hp to do so

 

[Beanmachine7000]

the instant mpg calculator is most likely accurate.. it all depends on throttle position.. say ur uncle is maintaining 70 mph on the freeway, its probably reading around 17-22 mpg, but if he eases off the throttle and starts to decelerate, the comp will read less fuel being sent but still high a mph. there fore it can calculate 40+ mpg at the moment of time.

my moms mini cooper has the instant mpg app. and wen ever u let off the gas completely, it shoots up to 99.9 mpg(which is the highest it reads) for the moment given.

open minded thinking, some of u guys shudd try it sometimes.

as for the op, 35 in 5th is prolly only a lil over idle but shoot if ur not hardly pressin the gas pedal then ur not bogging it.. its simply running an easy task of keeping a small ass truck at 35 mph. prolly only takes 3-4 hp to do so

Wow, I don't know where to start here... Instant fuel mileage will never be accurate... Does your mom's Mini actually get 99.9mpg? If it does, I'll buy it from her... It doesn't matter how much fuel is sent to the cylinder, it matters how much of that fuel is being used to generate work... Coasting and driving at extremely low RPM's are totally didfferent anyway... If you are driving at 35 in 5th, at say 1100RPM, then you are injecting the same amount of fuel (relatively) as at 3500RPM, but only 1100 times a minute, instead of 3500 times a minute... BUT, and this is a giant BUT, more of that fuel is going to be wasted as heat, therefore you WILL get less gas mileage... I'm very open minded (I'm a scientist, I have to be), but when things follow the laws of Physics (everything) then there is nothing to be open minded about... I'm not saying your truck will blow up if you drive at 35mph in 5th gear, but only that you wilol get worse gas mileage...

 

[TheTopher]

Instant fuel mileage is VERY accurate. We keep stating that it is the mileage for that exact moment, or "instant" if you will...which could very likely be why it's called "instant mileage" By the way, if you do your research you will find that most modern cars have a fuel cutoff feature, where if you let off the throttle entirely and the engine is above a certain rpm, in my old car it was 1250rpm the ecu will actually shut off the fuel injectors and the wheels will be turning the engine instead of vice versa, so at that particular "instant" the vehicle, a mini cooper in this case, really would be getting 99.9mpg because it's using NO GAS.

 

[Beanmachine7000]

Instant fuel mileage is VERY accurate. We keep stating that it is the mileage for that exact moment, or "instant" if you will...which could very likely be why it's called "instant mileage" By the way, if you do your research you will find that most modern cars have a fuel cutoff feature, where if you let off the throttle entirely and the engine is above a certain rpm, in my old car it was 1250rpm the ecu will actually shut off the fuel injectors and the wheels will be turning the engine instead of vice versa, so at that particular "instant" the vehicle, a mini cooper in this case, really would be getting 99.9mpg because it's using NO GAS.

Instant MPG might be accurate at telling how much fuel is going into the vehicle, but it has no way of measuring the efficiency at which that fuel is used... You cannot determine fuel mileage by injector output alone... If YOU would do your research you would realize that only vehicles equipped with manual transmissions stop firing injectors when you are coasting... This proverbial Mini Cooper will never get 99.9 mpg, if it does then I'm gonna go get me one!! I really don't give a rat's rear if it can coast without using gas, hell I can push my truck down a hill and it won't use gas either!!!

 

[TheTopher]

My last vehicle was an automatic, thank you very much, and it was still equiped with the fuel injector cutoff. And when you take the measurement of the fuel going into the engine and compare it to the speed of the vehicle, you can attain a fuel efficiency reading. For instance, lets say you are going 60 miles an hour and using fuel at a rate of .75 gallons per hour, at that particular moment you are getting 80mpg. Then lets say you hit a hill and you have to push the pedal harder to maintain speed, you're now adding more fuel into the engine, lets say now you're using 1.25 gallons per hour, to maintain that 60mph. Now you're only getting 48mpg. This is how the MPG guages work, by measuring the fuel going into the engine as compared to vehicle speed. This is not that complicated. I'm going to stop arguing here though, because this thread has gotten WAY off topic. If you want discuss it more PM me or start a new thread, please.

 

[jax4bangin]

Instant fuel mileage is VERY accurate. We keep stating that it is the mileage for that exact moment, or "instant" if you will...which could very likely be why it's called "instant mileage" By the way, if you do your research you will find that most modern cars have a fuel cutoff feature, where if you let off the throttle entirely and the engine is above a certain rpm, in my old car it was 1250rpm the ecu will actually shut off the fuel injectors and the wheels will be turning the engine instead of vice versa, so at that particular "instant" the vehicle, a mini cooper in this case, really would be getting 99.9mpg because it's using NO GAS.

thank u! thats exactly wat i was trying to say. had it in my head but not smart enough to put it in understandable txt lol

beanmachine- i understand where ur commin from and no the mini does not average 99.9 mpg, but it does pull 99.9 or better at that instant as stated

 

[Beanmachine7000]

I understand what both of you are saying, but you are both wrong, but I don't feel like arguing anymore... I'm not going to reply anymore...

 

[#1]

I'm very open minded (I'm a scientist, I have to be), but when things follow the laws of Physics (everything) then there is nothing to be open minded about...

Well guys, there are 3 of us here that actually understand the concept of instant mpg, but me must be idiots since the scientist has said we're wrong... and we all know that scientists have never been wrong before.

Well guess what, I'm a mechanic because I have to be, and as a mechanic I feel I have a better understanding of how a fuel injected internal combustion engine operates than you do as a scientist.

One point quick - don't you think "average mpg" is the average of all of your "instant mpg"? I'll answer for you - it is.


My EEC wants the engine to operate at an air/fuel ratio of 14.7:1 (might be 14.6 also, but it's close enough). When I have my throttle barely applied, there is only a small amount of air passing my throttle blade and entering the engine. My oxygen sensor senses how much oxygen is in the exhaust and sends the air/fuel ratio along with data from the air temp sensor, mass air flow sensor, coolant temp sensor, etc. to the computer who uses the information received to determine how much fuel to make the injectors inject into the cylinders. The oxygen sensors report what has happened and adjustments are made to the amount of fuel that the injectors inject during the next cycle to maintain an air/fuel ratio as close to 14.7:1 as possible.


Suppose you downshift a gear - the engine is now running at a higher rpm, which means most likely the throttle blade will be opened more also, which of course means more air is entering the engine. What happens when more air enters the engine? That's right, in order to maintain an air/fuel ratio of 14.7:1 there must be more gasoline mixed with the air. You are actually using more gas now to travel the same number of miles.


Just for kicks yesterday, I was driving at 35 mph in OD and set the accelerator pedal almost on the floor. The lowest the instant mpg went was around 21 mpg. How can this be possible? My throttle blade was nearly all the way open and the throttle position sensor was almost wide open. The engine was lugging hard! How in the world can I have still gotten 21 instant mpg? Because the engine rpm was still very low. A low engine rpm means that not much air is entering and leaving the engine, and again, in a effort to maintain an air/fuel ratio of 14.7:1, you guessed it - the injectors inject very little fuel into the engine.

When accelerating in first and second gear the instant mpg is very low, around 4 to 7. I'm not lugging the engine, though. Why the poor instant mpg? Ah, the rpm is high, meaning a lot of air entering and leaving the engine, which means a lot of fuel to maintain 14.7:1 while traveling at a very low speed.

You know what, I don't think the "instant mpg" computers are as stupid as you think they are.

It doesn't matter how much fuel is sent to the cylinder, it matters how much of that fuel is being used to generate work...

All of it is being used to generate work, otherwise it would not have been sent there.

The duty cycle of his injectors might be less because he is at a lower RPM, but his truck is creating more heat... His truck may be putting less fuel into the combustion chamber (which gives you good instant MPG) BUT, less of that fuel is going toward moving the vehicle, and more of it is going toward creating heat...

Less fuel = less heat. Physics dictates that. An engine can't decide how much of the fuel will move the vehicle and how much is heat. All of the fuel will move the vehicle, heat is determined by how much fuel is being burnt, which is very little in my case.

If you are driving at 35 in 5th, at say 1100RPM, then you are injecting the same amount of fuel (relatively) as at 3500RPM, but only 1100 times a minute, instead of 3500 times a minute...

It is not the same amount of fuel. The truck moves the same distance over the same time, but at a different mechanical advantage. Fourth gear will use the energy generated by the engine at a faster rate than fifth gear will. This means that more energy will have to be generated in fourth gear since it is used at a faster rate than in fifth gear to move the truck the same distance. This assumes that the engine is operating fairly efficiently in fifth, as my "instant mpg" indicates that it is.


I have an Explorer also. It's a '97 with a 5.0 and AWD with 189,000+ miles . I was getting an average of 18.8 mpg by doing the math at the pump. Then I bought a Scangauge II. The average mpg of the Scangauge was 18.8 also, just as I figured by doing the math at the pump, so I believe the Scangauge II to be accurate. By watching the "instant mpg", I was able to adjust the way I drive and bring my average to 21.7 mpg. Not bad for an AWD V8 Explorer.

 

[locovaca]

Suppose you downshift a gear - the engine is now running at a higher rpm, which means most likely the throttle blade will be opened more also, which of course means more air is entering the engine.

Not necessarily. Running at 65 mph I have to open the throttle more in 5th gear than I would running 500 rpm higher in 4th gear.

Just for kicks yesterday, I was driving at 35 mph in OD and set the accelerator pedal almost on the floor. The lowest the instant mpg went was around 21 mpg. How can this be possible? My throttle blade was nearly all the way open and the throttle position sensor was almost wide open. The engine was lugging hard! How in the world can I have still gotten 21 instant mpg? Because the engine rpm was still very low. A low engine rpm means that not much air is entering and leaving the engine, and again, in a effort to maintain an air/fuel ratio of 14.7:1, you guessed it - the injectors inject very little fuel into the engine.

I would throw some doubt into the accuracy of that calculation if that's the number it was putting out.

When accelerating in first and second gear the instant mpg is very low, around 4 to 7. I'm not lugging the engine, though. Why the poor instant mpg? Ah, the rpm is high, meaning a lot of air entering and leaving the engine, which means a lot of fuel to maintain 14.7:1 while traveling at a very low speed.

Or, because of Newton's laws of motion. You're moving 1.5 tons from 0-25 in just a few seconds. When you're on the interstate and decide to go from 55-65 you not only are increasing your speed less, you are typically also doing it over a longer period of time. Try accelerating from 0 to 25 over the course of 30 seconds, you'll see that instantaneous MPG stay high.

You know what, I don't think the "instant mpg" computers are as stupid as you think they are.

All of it is being used to generate work, otherwise it would not have been sent there.

No. There is no 100% efficient conversion of energy in existence. Most of the conversion is wasted as heat.

Try this: try pushing your truck on level ground from a stop. Now use the same effort to used to push it on level ground but up a hill. Same amount of input energy, but one corresponds into 100% heat loss and 0% motion energy.

Less fuel = less heat. Physics dictates that. An engine can't decide how much of the fuel will move the vehicle and how much is heat. All of the fuel will move the vehicle, heat is determined by how much fuel is being burnt, which is very little in my case.

It depends on the ratios. When running in 5th at 1000 rpm nearly all of your fuel is being wasted as heat. If you were running at 2500 rpm in 3rd you might have more absolute fuel (depending on the throttle position) going to the engine, but now only 70% of that wasted as heat.

Remember: efficiency is Miles per gallon. If you're dumping less fuel into the engine but almost all of it is being wasted as heat, that's just as bad as running at a super high RPM.

It is not the same amount of fuel. The truck moves the same distance over the same time, but at a different mechanical advantage. Fourth gear will use the energy generated by the engine at a faster rate than fifth gear will. This means that more energy will have to be generated in fourth gear since it is used at a faster rate than in fifth gear to move the truck the same distance. This assumes that the engine is operating fairly efficiently in fifth, as my "instant mpg" indicates that it is.

The energy is generated by the piston going down. The amount of resistance encountered by that piston will dictate the efficiency of the stroke. 5th gear will cause more resistance because it has to generate the same amount of torque but with fewer rpms to do so.

Consider this analogy: You own a theme park that has to be cleaned up every day. You give everyone who helps clean it up at least one free meal in addition to their hourly pay. If you hire too few people, you "save" some money in the # of workers but everyone has to work very hard to get everything done, they stay all day and get three meals. If you hire too many people, they get the done quickly but still cash in on their free meal which ends up costing you more money than you should have. You are looking for the right combo of workers who can get the park cleaned up in a few hours, get their meal, and leave.

I have an Explorer also. It's a '97 with a 5.0 and AWD with 189,000+ miles . I was getting an average of 18.8 mpg by doing the math at the pump. Then I bought a Scangauge II. The average mpg of the Scangauge was 18.8 also, just as I figured by doing the math at the pump, so I believe the Scangauge II to be accurate. By watching the "instant mpg", I was able to adjust the way I drive and bring my average to 21.7 mpg. Not bad for an AWD V8 Explorer.

Your gains probably came from accelerating slower (see above), slowing for red lights early and hitting them in stride, etc.. In my Accord I tried that last summer when gas prices shot through the roof and I increased from 28-29 MPG to 35 MPG. Nothing magical, just driving smart.

Also see here for the classic Bike example: http://www.cartalk.com/content/columns/Archive/2005/August/07.html

 

[#1]

Your gains probably came from accelerating slower (see above), slowing for red lights early and hitting them in stride, etc.. In my Accord I tried that last summer when gas prices shot through the roof and I increased from 28-29 MPG to 35 MPG. Nothing magical, just driving smart.

I already drove fairly slow and smart, but the Scangauge helped my fine tune my driving styles.

It helped a lot for highway mpg since I could watch the instant mpg and get a "feel" for what type of mileage I was getting, then go 5 mph faster/slower to see how it changed and then travel at the speed that yielded the best mpg.

Anyway, my point was that the "instant mpg" must be accurate, otherwise my average mpg would have not increased.

Accelerating too slow can also hurt mpg since the car stays in a lower, less fuel efficient gear for longer than it would if you were to accelerate quicker. There is an in between rate of acceleration for the best mpg.



Earlier tonight I set the Scangauge to display instant mpg, throttle position, and gallons per hour. I drove at a constant 35 mph on flat, straight ground with a very steady gas pedal.

In 4th gear the TPS was 23 and the gallons per hour was 1.08 to 1.10

In 5th gear the TPS was 21 and the gallons per hour was .90 to .93

Again, 5th gear in my truck will get better mpg than 4th will.



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[fastpakr]

Not a chance.