Anyone try cutting motor off at traffic lights to see MPG savings?
06-12-2008, 05:56 PM
#81
-Arsenic-
I didn't mean wear and tear on just the starter. The main reason startup is so hard on engines, is because when the engine is off, the oil goes to the oilpan. So for that second or two during startup, the oil is not on the main moving parts of the engine yet.
06-12-2008, 06:08 PM
#82
Drifting
Originally Posted by phee
it would be more efficient to throw your car in nuetral when coming up to a light (even if its green) this way your cruising at idle speeds and your momentum is not lost. you would have to be really good at timing yourself if you wanted to shut off and on. its not worth it and coasting will save you more gas, as well as using cruise control to accelerate and minimizing brake usage
In fact here is what it says in the Toyota Service Manual:
Deceleration Fuel Cut
During closed throttle deceleration periods from moderate to high engine speeds, fuel delivery is not necessary or desirable. To prevent excessive decel emissions and improve fuel economy, the ECM will not open the fuel injectors under certain decel conditions. The ECM will resume fuel injection at a calculated RPM.
During closed throttle deceleration periods from moderate to high engine speeds, fuel delivery is not necessary or desirable. To prevent excessive decel emissions and improve fuel economy, the ECM will not open the fuel injectors under certain decel conditions. The ECM will resume fuel injection at a calculated RPM.
Here is a video of a diagnostic tool plugged into the OBD-II port of a Honda Civic, showing the fuel-injector pulse getting reduced to 0.0 when coasting. (It's not my video)
Video Link
06-12-2008, 06:11 PM
#83
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Why is the fuel cut when you're coasting but not when you're idling at a stop?
06-12-2008, 06:15 PM
#85
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Originally Posted by Fyre Man
Why is the fuel cut when you're coasting but not when you're idling at a stop?
06-12-2008, 06:18 PM
#86
Drifting
Originally Posted by Fyre Man
Why is the fuel cut when you're coasting but not when you're idling at a stop?
If you are idling at a stop, and you cut fuel, the engine stops turning. If you reapply fuel, you'll flood the engine. You need to actually engage the starter before you can reapply fuel
GM has a system called BAS (Belt Alternator Starter), that combines the alternator and the starter. It stops the engine when you are stopped at a light. PResumably, it's easier (and smoother) to restart the engine with the starter and alternator integrated, rathre than having to use a traditional starter and solenoid, etc...
That system doesn't really improve your fuel economy much tho. I think in real world it increased fuel economy like 2% or something like that.
06-12-2008, 06:29 PM
#88
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Here's my idea to improve your fuel economy, at the cost of performance though. Stuff a sock in front of your air cleaner. You'll get off the line slower, but getting the car moving is what costs alot of gas. The computer will just automatically adjust for less airflow/less fuel to the injectors. Not sure what happens at WOT though.... I know, crazy idea.
06-12-2008, 06:39 PM
#89
AZ Community Team
On a warmed up engine, the startup wear is pratically neglicableon startup. The oil filters anti-drainback valve also protects this. The internal contact friction engine parts have a nice oil film on them. Cold engines is a different story where oil and engine parts are cold, and wear is a issue.
Hybrid car's ECU deliberatey wait until the engine is warmed up before they start to shutdown and restart the engine. Not only for wear but also emissions since the cat is also not fully hot yet.
Hybrid car's ECU deliberatey wait until the engine is warmed up before they start to shutdown and restart the engine. Not only for wear but also emissions since the cat is also not fully hot yet.
Originally Posted by 02type-s
I didn't mean wear and tear on just the starter. The main reason startup is so hard on engines, is because when the engine is off, the oil goes to the oilpan. So for that second or two during startup, the oil is not on the main moving parts of the engine yet.
06-12-2008, 06:43 PM
#90
Drifting
Originally Posted by Legend2TL
On a warmed up engine, the startup wear is pratically neglicableon startup. The oil filters anti-drainback valve also protects this. The internal contact friction engine parts have a nice oil film on them. Cold engines is a different story where oil and engine parts are cold, and wear is a issue.
Hybrid car's ECU deliberatey wait until the engine is warmed up before they start to shutdown and restart the engine. Not only for wear but also emissions since the cat is also not fully hot yet.
Hybrid car's ECU deliberatey wait until the engine is warmed up before they start to shutdown and restart the engine. Not only for wear but also emissions since the cat is also not fully hot yet.
06-13-2008, 01:31 AM
#91
Originally Posted by avs007
When you are coasting, the wheels are keeping the engine turning, so when fuel is reapplied, the engine keeps humming...
If you are idling at a stop, and you cut fuel, the engine stops turning. If you reapply fuel, you'll flood the engine. You need to actually engage the starter before you can reapply fuel
If you are idling at a stop, and you cut fuel, the engine stops turning. If you reapply fuel, you'll flood the engine. You need to actually engage the starter before you can reapply fuel
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
06-13-2008, 02:09 AM
#92
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you're putting major wear and tear on your battery, starter, and motor...when the engine is spinning very slow (starting speeds), it has no oil pressure and the cylenders run dry for a second until oil pressure builds up and gets to the cylenders...let's not even start to talk how much wear you're putting on your starter...a new battery and starter are not worth the gas you think you're saving...if any at all. when the engine starts the starter only spins it at a few hundred rmp and rams gas in the cylenders to start..which is why i doubt you save anything at all, it's all in your conience, you drive even slower now to save more gas.
06-13-2008, 03:37 AM
#93
05' AT SSM
I saw a huge thing about this on CNN, some reporter took a drive with this guy called a "hyper miler" in fact search Hyper Miling in google, tons of stuff comes up.
I laughed when i watched this guy turn his car off, so dangerous... and like the above poster stated "putting major wear and tear.."
If you want to save gas sell your TL and buy a crappy hybrid hahahah
Interesting topic, i might lose my passenger seat and spare tire to save gas..see if it works =D
I laughed when i watched this guy turn his car off, so dangerous... and like the above poster stated "putting major wear and tear.."
If you want to save gas sell your TL and buy a crappy hybrid hahahah
Interesting topic, i might lose my passenger seat and spare tire to save gas..see if it works =D
06-13-2008, 05:08 AM
#94
Registered Member
I have found that my '04 manual TL is somewhat sensitive to tires. The stock Bridgestone EL42's, which are classed as Grand Touring tires, delivered great fuel economy, which I suspect is one of the primary reasons that Acura spec'd these tires as the OEM factory shoes.
With the stock EL42's I consistently managed around 25.5 to 26 MPG for my weekly work commute which was virtually all in-town and residential driving (lights, stop signs, traffic, school buses...). The best I got was 27.98 under these conditions and in the summer months when fuel economy increases. And the best I ever managed on the highway was 33.94 MPG and that was on a vacation trip in the summer with the A/C running the whole time.
Two years ago, I had a set of Michelin Pilot Sport A/S tires installed on my wheels and as soon as I put the wheels back on the car and backed it out of my garage, the rolling resistance was immediately felt. My work commute MPG dropped to the mid 24's and the best highway mileage I have gotten with these tires is a little over 32 MPG.
So when replacing your tires, if fuel economy is your thing, get a high quality set of Touring or Grand Touring tires. Expect to lose some handling with these. I have been following a set of Ultra High Performance all-season tires which do look quite promising. The B.F.Goodrich g-Force Super Sport A/S tires may be up for serious consideration the next time around.
With the stock EL42's I consistently managed around 25.5 to 26 MPG for my weekly work commute which was virtually all in-town and residential driving (lights, stop signs, traffic, school buses...). The best I got was 27.98 under these conditions and in the summer months when fuel economy increases. And the best I ever managed on the highway was 33.94 MPG and that was on a vacation trip in the summer with the A/C running the whole time.
Two years ago, I had a set of Michelin Pilot Sport A/S tires installed on my wheels and as soon as I put the wheels back on the car and backed it out of my garage, the rolling resistance was immediately felt. My work commute MPG dropped to the mid 24's and the best highway mileage I have gotten with these tires is a little over 32 MPG.
So when replacing your tires, if fuel economy is your thing, get a high quality set of Touring or Grand Touring tires. Expect to lose some handling with these. I have been following a set of Ultra High Performance all-season tires which do look quite promising. The B.F.Goodrich g-Force Super Sport A/S tires may be up for serious consideration the next time around.
06-13-2008, 06:09 AM
#95
AZ Community Team
Nope, it's the truth virtually every electronic fuel injection system every made does this. When the engine is above ~1200-1500 RPM and the throttle is closed, then the ECU shuts off all fuel to the injectors. If the throttle is opened or the engine RPM drops below 1500 RPM then the fuel is started again to the appropiate air flow fuel mapping (air/fuel ratio). This is very well explained in the TL shop manual, it's even explained in the Acura shop manual for my 1986 Prelude Si.
So as long as the vehicle has enough momentum to keep the engine turning with the car in gear, clutch not enaged, and the throttle closed, and the engine RPM above ~1200 RPM no fuel is injected. Going down a hill that saves fuel.
So as long as the vehicle has enough momentum to keep the engine turning with the car in gear, clutch not enaged, and the throttle closed, and the engine RPM above ~1200 RPM no fuel is injected. Going down a hill that saves fuel.
Originally Posted by scv76_
I find what you are saying to be hard to believe....if the fuel were cut off to the injectors while coasting in gear, the engine will surely die...requiring the starter to be re-engaged to continue driving once fuel was once again supplied. I suppose you could dump the clutch on a manual transmission instead of using the starter.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
06-13-2008, 07:45 AM
#96
Suzuka Master
Originally Posted by scv76_
I find what you are saying to be hard to believe....if the fuel were cut off to the injectors while coasting in gear, the engine will surely die...requiring the starter to be re-engaged to continue driving once fuel was once again supplied. I suppose you could dump the clutch on a manual transmission instead of using the starter.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
06-13-2008, 08:30 AM
#97
AZ Community Team
I have a feeling that the EL42's are commonly used as OEM tires for their low rolling resistance to up the CAFE fuel economy numbers for a manufacturers line of vehicles. I saw them yesterday twice on a new BMW 325 and Toyota minivan. They are used across a wide range of OEM applications.Very similar to the Michelin MXV4 Energy series which were used extensively on Honda/Acura's and many Detroit products. The Energy series had much lower rolling resistance and friction than the standard MXV's. There were several articles about those tires getting better gas mileage that the owners were perplexed when their fuel economy dropped with non-Energy tire replacements.
Originally Posted by SouthernBoy
I have found that my '04 manual TL is somewhat sensitive to tires. The stock Bridgestone EL42's, which are classed as Grand Touring tires, delivered great fuel economy, which I suspect is one of the primary reasons that Acura spec'd these tires as the OEM factory shoes.
With the stock EL42's I consistently managed around 25.5 to 26 MPG for my weekly work commute which was virtually all in-town and residential driving (lights, stop signs, traffic, school buses...). The best I got was 27.98 under these conditions and in the summer months when fuel economy increases. And the best I ever managed on the highway was 33.94 MPG and that was on a vacation trip in the summer with the A/C running the whole time.
Two years ago, I had a set of Michelin Pilot Sport A/S tires installed on my wheels and as soon as I put the wheels back on the car and backed it out of my garage, the rolling resistance was immediately felt. My work commute MPG dropped to the mid 24's and the best highway mileage I have gotten with these tires is a little over 32 MPG.
So when replacing your tires, if fuel economy is your thing, get a high quality set of Touring or Grand Touring tires. Expect to lose some handling with these. I have been following a set of Ultra High Performance all-season tires which do look quite promising. The B.F.Goodrich g-Force Super Sport A/S tires may be up for serious consideration the next time around.
With the stock EL42's I consistently managed around 25.5 to 26 MPG for my weekly work commute which was virtually all in-town and residential driving (lights, stop signs, traffic, school buses...). The best I got was 27.98 under these conditions and in the summer months when fuel economy increases. And the best I ever managed on the highway was 33.94 MPG and that was on a vacation trip in the summer with the A/C running the whole time.
Two years ago, I had a set of Michelin Pilot Sport A/S tires installed on my wheels and as soon as I put the wheels back on the car and backed it out of my garage, the rolling resistance was immediately felt. My work commute MPG dropped to the mid 24's and the best highway mileage I have gotten with these tires is a little over 32 MPG.
So when replacing your tires, if fuel economy is your thing, get a high quality set of Touring or Grand Touring tires. Expect to lose some handling with these. I have been following a set of Ultra High Performance all-season tires which do look quite promising. The B.F.Goodrich g-Force Super Sport A/S tires may be up for serious consideration the next time around.
06-13-2008, 09:09 AM
#98
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Originally Posted by scv76_
I find what you are saying to be hard to believe....if the fuel were cut off to the injectors while coasting in gear, the engine will surely die...requiring the starter to be re-engaged to continue driving once fuel was once again supplied. I suppose you could dump the clutch on a manual transmission instead of using the starter.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this, but then why isn't the Accords milage any better than it is?
Some one on a 6 mile down hill do some experiments by re-setting the trip computer while coasting in gear, then repeat the experiment coasting in neutral.
Coasting downhill in gear at 70 mph requires about 2000 rpm's, coasting at 70 in neutral requires only about 800 rpm's...gotta use more gas at 2000 than 800.
06-13-2008, 09:17 AM
#99
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Originally Posted by Legend2TL
Nope, it's the truth virtually every electronic fuel injection system every made does this. When the engine is above ~1200-1500 RPM and the throttle is closed, then the ECU shuts off all fuel to the injectors. If the throttle is opened or the engine RPM drops below 1500 RPM then the fuel is started again to the appropiate air flow fuel mapping (air/fuel ratio). This is very well explained in the TL shop manual, it's even explained in the Acura shop manual for my 1986 Prelude Si.
So as long as the vehicle has enough momentum to keep the engine turning with the car in gear, clutch not enaged, and the throttle closed, and the engine RPM above ~1200 RPM no fuel is injected. Going down a hill that saves fuel.
So as long as the vehicle has enough momentum to keep the engine turning with the car in gear, clutch not enaged, and the throttle closed, and the engine RPM above ~1200 RPM no fuel is injected. Going down a hill that saves fuel.
06-13-2008, 11:43 AM
#100
Drifting
Originally Posted by scv76_
I don't believe our current TL models have cylinder management (meaning some cylinders are shut down when not needed) I heard the Accord has this
The main reason for Deceleration-Fuel-Cut is emissions. If the ECU didn't completely cut the fuel, you would have very high NOx levels while coasting because of the the lean condition that would have resulted from the negative load on the engine.
That's why on a non fuel injected engines, under the same condition, when you coast from mid-high engine RPM, the fuel/air mixture typically defaults to going rich. Different solution to the same problem.
06-13-2008, 01:23 PM
#101
AZ Community Team
Originally Posted by avs007
What I'm talking about only occurs when you are coasting. What you are talking about in the Accord is active when you are cruising. (ie, still applying pressure on the accelerator).
The main reason for Deceleration-Fuel-Cut is emissions. If the ECU didn't completely cut the fuel, you would have very high NOx levels while coasting because of the the lean condition that would have resulted from the negative load on the engine.
That's why on a non fuel injected engines, under the same condition, when you coast from mid-high engine RPM, the fuel/air mixture typically defaults to going rich. Different solution to the same problem.
The main reason for Deceleration-Fuel-Cut is emissions. If the ECU didn't completely cut the fuel, you would have very high NOx levels while coasting because of the the lean condition that would have resulted from the negative load on the engine.
That's why on a non fuel injected engines, under the same condition, when you coast from mid-high engine RPM, the fuel/air mixture typically defaults to going rich. Different solution to the same problem.
Anybody who's ever worked on a mid to late 70's Japanese car with a carburator has surely seen the incredible rats nest of numbered (yes gotta love the Japanese way!) vacuum hoses for emissions purposes. The number of vacuum hoses on the 3G Tl is probably 5-7 times less than a 1976 Honda Accord CVCC!
06-13-2008, 01:24 PM
#102
AZ Community Team
Originally Posted by vincethe1
you mean clutch engaged (as in not seperated, not pushed in)
06-13-2008, 01:50 PM
#103
Instructor
My $0.02 -
Don't shut off the engine at red lights, either long or short ones. Certainly if you are going to pick up your kids at school or something, and need to park and wait for 5 minutes or longer, do shut off the engine (unless you live in the Sacramento area like I do and it's 110 degrees and you need the A/C running while you're parked).
But shutting it off at red lights is not what the car was designed to withstand. As many others have pointed out, the engine and the starter are not designed for that. There could be significant wear and tear. Excess fuel is consumed when starting. There are safety risks having no engine running while sitting on the road. And all the in-car electronics will reset every time you do it.
Hybrids are very different animals and have a number of special design features to mitigate these issues. For example, they can use the big electric motor to spool up the engine without a significant amount of fuel lost or wear on the starter motor (which is a different and much smaller component).
I'm not a car design engineer (though I am an engineer) but my gut tells me the benefits of cutting the motor for a red light are FAR overshadowed by the drawbacks.
Don't shut off the engine at red lights, either long or short ones. Certainly if you are going to pick up your kids at school or something, and need to park and wait for 5 minutes or longer, do shut off the engine (unless you live in the Sacramento area like I do and it's 110 degrees and you need the A/C running while you're parked).
But shutting it off at red lights is not what the car was designed to withstand. As many others have pointed out, the engine and the starter are not designed for that. There could be significant wear and tear. Excess fuel is consumed when starting. There are safety risks having no engine running while sitting on the road. And all the in-car electronics will reset every time you do it.
Hybrids are very different animals and have a number of special design features to mitigate these issues. For example, they can use the big electric motor to spool up the engine without a significant amount of fuel lost or wear on the starter motor (which is a different and much smaller component).
I'm not a car design engineer (though I am an engineer) but my gut tells me the benefits of cutting the motor for a red light are FAR overshadowed by the drawbacks.
06-13-2008, 02:40 PM
#104
Cruisin'
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Rpm
Originally Posted by jumbosizeme79
so are you saying that if i leave my car on in park, it would waste more gas then if i continually started up and shut of my car every i dont know 30- 45 secs?
06-13-2008, 03:18 PM
#105
Drifting
Originally Posted by Legend2TL
Rapid closure of the throttle results in a rich fuel mixture which cuases the high NOx
Of course this wastes fuel, so I'm sure there were better ways. I was just illustrating why the ECU on a fuel injection system will completely cut-off the fuel during deceleration. Emissions primary and efficiency secondary. At least that's how it's described in Toyota's service manual.
06-13-2008, 03:24 PM
#106
Drifting
Besdies, the Honda CVCC is a bad example, becuase the CVCC was the only car that was able to meet emissions requirements at the time without the use of a Catalytic converter.
06-13-2008, 03:55 PM
#107
AZ Community Team
Originally Posted by avs007
Besdies, the Honda CVCC is a bad example, becuase the CVCC was the only car that was able to meet emissions requirements at the time without the use of a Catalytic converter.
06-13-2008, 03:59 PM
#108
AZ Community Team
Yes, you correct the NOx is due to high combustion temps. However the richer mixture on a carburatored engine when the throttle is closed increased the CO and particulates.
They still used dashpots on 80's Honda's and Acura's with PGM-FI to still allow more air into the cylinders momentarily even though the fuel was shutdown when the throttle was dropped. Still emission related I guess.
They still used dashpots on 80's Honda's and Acura's with PGM-FI to still allow more air into the cylinders momentarily even though the fuel was shutdown when the throttle was dropped. Still emission related I guess.
Originally Posted by avs007
High NOx is caused by a lean condition, not a rich condition. High NOx is a result of excessive combustion temperature. A rich condition does not contribute to this, in fact a rich condition lowers combustion temperatures, which is why non fuel injected systems typically used to go rich on high-rpm deceleration.
Of course this wastes fuel, so I'm sure there were better ways. I was just illustrating why the ECU on a fuel injection system will completely cut-off the fuel during deceleration. Emissions primary and efficiency secondary. At least that's how it's described in Toyota's service manual.
Of course this wastes fuel, so I'm sure there were better ways. I was just illustrating why the ECU on a fuel injection system will completely cut-off the fuel during deceleration. Emissions primary and efficiency secondary. At least that's how it's described in Toyota's service manual.
06-13-2008, 04:10 PM
#109
Originally Posted by avs007
I was just illustrating why the ECU on a fuel injection system will completely cut-off the fuel during deceleration
If the fuel is completely shut off during deceleration, how does the car keep running and why don't I have to re-start it after a prolonged deceleration?
06-13-2008, 04:21 PM
#110
Drifting
Originally Posted by scv76_
I'm still stumbling on this...
If the fuel is completely shut off during deceleration, how does the car keep running and why don't I have to re-start it after a prolonged deceleration?
If the fuel is completely shut off during deceleration, how does the car keep running and why don't I have to re-start it after a prolonged deceleration?
When the ECU resumes fueling the engine, the internal combustion of the engine supplies additional power. You don't have to "start" the engine by cranking the starter again because the engine was already rotating. (All the starter does is rotate the engine)
06-13-2008, 04:22 PM
#111
Drifting
Originally Posted by Legend2TL
Naa, the CVCC is a great example of 70's classic pneumatic computation and servo control of emissions systems. Worked on a 1976 CVCC a few times, I can laugh at it now but back then it was not fun at all getting it through emissions!
06-13-2008, 04:39 PM
#112
2004 SSM/EB/5AT/Navi/RSB
Originally Posted by avs007
What's your definition of "running"? That the engine is still rotating? If so, the engine is still "running" with fuel cut off while you are decelerating. The engine is rotating, because it is being forced to turn by the fact that the wheels are still turning, which is turning the drive shaft, which is turning the engine.
When the ECU resumes fueling the engine, the internal combustion of the engine supplies additional power. You don't have to "start" the engine by cranking the starter again because the engine was already rotating. (All the starter does is rotate the engine)
When the ECU resumes fueling the engine, the internal combustion of the engine supplies additional power. You don't have to "start" the engine by cranking the starter again because the engine was already rotating. (All the starter does is rotate the engine)
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.
06-13-2008, 04:58 PM
#114
Drifting
Originally Posted by bluenoise
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.
If you are in park, and you rev to 3000rpm, the engine load value will still be near 0%. However if you are cruising at 1700rpm on the freeway in top gear, this value will be higher. In this particular case, the fuel-injector pulse width will be smaller for the 3000rpm in park, because less fuel is needed to turn the engine that fast, compared to the cruising on the hwy.
For those that are confused, think of it this way:
Assuming a constant speed, are you burning the same amount of calories on a treadmill regardless of what the incline is? Think of incline as engine load. Just because you are walking faster doesn't necessarily mean you are burning more calories.
06-13-2008, 05:56 PM
#115
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Originally Posted by bluenoise
Thank you for saving me a bunch of typing. Even in the 5AT, the fuel is completely cut off when coasting under closed throttle. Before I upgraded my navi's version, I was able to bring up the diagnostics screen on the navi that showed, among other things, the amount of fuel the engine was burning per second. If I sat at a light idling, I was using somewhere around 0.2 to 1.0 mL/second. If I coasted in neutral, I'd see the same number, since the engine was just idling. If I coasted in gear, though, the number would go to 0.0 mL/second as the car's computer is smart enough to know no fuel is needed to keep it turning over.
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.
06-15-2008, 12:23 AM
#116
Originally Posted by avs007
This is actually not true. It uses more gas to coast in neutral than to coast in drive. The ECU will cut fuel to the fuel injectors when you are coasting. It's called "Deceleration Fuel Cut". Pretty much all fuel-injected systems do this.
In fact here is what it says in the Toyota Service Manual:
If you coast in neutral, the fuel will not get cut when you coast.
In fact here is what it says in the Toyota Service Manual:
If you coast in neutral, the fuel will not get cut when you coast.
Interesting, learned something today. It has crossed my mind before whether it really did work that way.
06-15-2008, 01:41 AM
#117
Something is missing...my
Originally Posted by SporkLover
It's an interesting notion..... I wonder what effect the constant starting and stopping of the engine would have on the longevity on some of the internals and the starter itself.
I know Hybrid engines do exactly this..... but was there some special consideration when their engine was designed for this type of duty?
I know Hybrid engines do exactly this..... but was there some special consideration when their engine was designed for this type of duty?
This almost resembles the old "can I use lowgrade gas" arguement. Is it really worth it? Not IMO. Interesting to see the results.
06-15-2008, 02:02 AM
#119
Cruisin'
Join Date: Jul 2007
Age: 59
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Originally Posted by LaCostaRacer
With gas prices and MPG being such a hot topic, I thought I started
an experiment with killing my motor and stop lights. I understand
the Japanese and Europeans have been this trick for some time. I
just started today so my data is pretty preliminary but I think my
(all-city) commute to work will see an improvement in MPG by 1 or 2
possibly. I encounter about 2-6 lights per direction in my daily
commute and my average speed on the MID is usually around 24-27mph
depending on highway miles on the weekend mostly.
Here are the situations where I'll kill my motor:
1. light turns red as you approach intersection- you couldn't push
the yellow (we have camaras) and you're stuck waiting an entire
2-4 minute light cycle.
2. you're in a long queue of cars at an intersection and you think
you're mid-way or less through a light cycle. You have gobs of
time to restart you car because there are 10 cars ahead of you
that need to start moving.
I just filled up today so I won't know if this makes any difference
for a week or two but thought it might be interesting to find out.
My quick 1 mile drive from Costco to work yeilded 15 MPG (kill motor
1/3 lights in the drive) and I had 15 MPG instead of the typical
7-12 so it seems to make a difference in this hyper-example anyway.
Has anyone done this with the TL? Did you find a MPG improvement? I
hear if you can beat restarting you car for 30 or more seconds it's
a savings but that may have been factoring $2.00 gas- maybe it's 15
seconds with $4.52 Costco Premium.
I did a search and didn't find anything here or even cartalk.
Please no comments on why you bought a TL- this is just an
experiment more than anything. I haven't heard from any Americans
about this practice so I thought I would check with my favorite TL
car people.
an experiment with killing my motor and stop lights. I understand
the Japanese and Europeans have been this trick for some time. I
just started today so my data is pretty preliminary but I think my
(all-city) commute to work will see an improvement in MPG by 1 or 2
possibly. I encounter about 2-6 lights per direction in my daily
commute and my average speed on the MID is usually around 24-27mph
depending on highway miles on the weekend mostly.
Here are the situations where I'll kill my motor:
1. light turns red as you approach intersection- you couldn't push
the yellow (we have camaras) and you're stuck waiting an entire
2-4 minute light cycle.
2. you're in a long queue of cars at an intersection and you think
you're mid-way or less through a light cycle. You have gobs of
time to restart you car because there are 10 cars ahead of you
that need to start moving.
I just filled up today so I won't know if this makes any difference
for a week or two but thought it might be interesting to find out.
My quick 1 mile drive from Costco to work yeilded 15 MPG (kill motor
1/3 lights in the drive) and I had 15 MPG instead of the typical
7-12 so it seems to make a difference in this hyper-example anyway.
Has anyone done this with the TL? Did you find a MPG improvement? I
hear if you can beat restarting you car for 30 or more seconds it's
a savings but that may have been factoring $2.00 gas- maybe it's 15
seconds with $4.52 Costco Premium.
I did a search and didn't find anything here or even cartalk.
Please no comments on why you bought a TL- this is just an
experiment more than anything. I haven't heard from any Americans
about this practice so I thought I would check with my favorite TL
car people.
06-15-2008, 02:48 AM
#120
Racer
Join Date: Jan 2004
Location: Calabasas, California
Age: 37
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Originally Posted by bluenoise
Thank you for saving me a bunch of typing. Even in the 5AT, the fuel is completely cut off when coasting under closed throttle. Before I upgraded my navi's version, I was able to bring up the diagnostics screen on the navi that showed, among other things, the amount of fuel the engine was burning per second. If I sat at a light idling, I was using somewhere around 0.2 to 1.0 mL/second. If I coasted in neutral, I'd see the same number, since the engine was just idling. If I coasted in gear, though, the number would go to 0.0 mL/second as the car's computer is smart enough to know no fuel is needed to keep it turning over.
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.
Another example of why higher RPM doesn't necessarily mean more fuel usage is when coasting downhill in gear. The RPM may be pretty high on a steep decline, but the fuel used with be zero.