Shifting auto tranny from "D" to "N" at stop lights for fuel economy
09-14-06, 09:55 PM
#31
Tech Info Resource
iTrader: (2)
The FSM doesn't agree with you al503.
FC IDL
Fuel cut idle: ON or OFF
ON: Fuel cut operating
FC IDL = "ON" when throttle valve fully closed and engine speed over 2,800 rpm
FC TAU
Fuel cut TAU (Fuel cut during very light load): ON or OFF
ON: Fuel cut operating
Fuel cut being performed under very light load to prevent engine combustion from becoming incomplete
Fuel cut idle: ON or OFF
ON: Fuel cut operating
FC IDL = "ON" when throttle valve fully closed and engine speed over 2,800 rpm
FC TAU
Fuel cut TAU (Fuel cut during very light load): ON or OFF
ON: Fuel cut operating
Fuel cut being performed under very light load to prevent engine combustion from becoming incomplete
09-14-06, 10:00 PM
#32
Lexus Champion
I wouldn't be surprised at all if the ECU starts delivering some fuel and spark at 1K RPMs. If it waited for the engine to reach idle speed exactly, it would stumble for a second on rapid RPM drops. However, if you monitor the AFR via WBO2 as you engine braked from 60 to 0, I'm sure you would see 20.9:1 until you got to around 10 MPH.
09-14-06, 10:01 PM
#33
Tech Info Resource
iTrader: (2)
^^see my post above...
09-14-06, 10:02 PM
#34
Lexus Champion
09-14-06, 10:05 PM
#35
Tech Info Resource
iTrader: (2)
I found a better answer from the FSM, should be crystal clear:
And this too...
Fuel-cut is performed when the following conditions are met:
• Accelerator pedal fully released.
• Engine speed is 2,500 rpm or more (fuel injection returns at 1,000 rpm).
• Accelerator pedal fully released.
• Engine speed is 2,500 rpm or more (fuel injection returns at 1,000 rpm).
• The ECM stops fuel injection (fuel cut) during engine deceleration. This causes a lean condition and results in a momentary increase in the A/F sensor output voltage.
• The ECM must establish a closed throttle valve position learning value to perform fuel cut. If the battery terminal has been reconnected, the vehicle must be driven over 16 km/h (10 mph) to allow the ECM terminal to be reconnected, the vehicle must be driven at over 16 km/h (10 mph) to allow the ECM to learn the closed throttle valve position.
• The ECM must establish a closed throttle valve position learning value to perform fuel cut. If the battery terminal has been reconnected, the vehicle must be driven over 16 km/h (10 mph) to allow the ECM terminal to be reconnected, the vehicle must be driven at over 16 km/h (10 mph) to allow the ECM to learn the closed throttle valve position.
Last edited by lobuxracer; 09-14-06 at 10:15 PM. Reason: Better answer
09-14-06, 10:11 PM
#37
Lexus Champion
Thanks for the translation. Again, not disputing what it says. Just calling it like I've seen it. Try it yourself. Find a flat, empty stretch and cruise at about 20-30 mph or where you're just turning over 1K rpms. Take your foot off the pedal and look at the gauge.
09-14-06, 10:13 PM
#38
Lexus Champion
Ken,
If "N" was for towing, then why is it right next to "D" with no obstruction in shifter movement? If I were designing it specifically for towing, I would put it right next to "P".
Again, this isn't about saving $1 each month on fuel. This is an experiment on how close I can get my city mileage to highway mileage. I don't see it any differently to anyone else tyring to see how quickly they can do a 1/4 mile, or how impressive their dyno plots can look.
If "N" was for towing, then why is it right next to "D" with no obstruction in shifter movement? If I were designing it specifically for towing, I would put it right next to "P".
Again, this isn't about saving $1 each month on fuel. This is an experiment on how close I can get my city mileage to highway mileage. I don't see it any differently to anyone else tyring to see how quickly they can do a 1/4 mile, or how impressive their dyno plots can look.
When you tow a vehicle, you need to put the car in D first, then in N. You shouldn't go from R to N.
R is next to P because from P when you want to back up your car, you don't want to go into D first.
As far as design, I wasn't around when they were designing the gear sequence, it could have been something as simple as there was no Park, only R, N, and D and so no obstruction any place except when going into reverse. I dunno. But I think neutral was where you started cars that didn't have a Park.
09-14-06, 10:17 PM
#39
I'm trying to derive a test to see how much more fuel efficient it is to idle in "N" than it is in "D". The only idea I can come up with is to reset the "AVG MPG" at the same moment I'm doing a high rate of speed on the highway (ie. 100 MPH) and engine brake to nearly a stop. Once I'm at a stop, the AVG MPG would be really high, but would drop quickly. I imagine that the AVG MPG would be well over 50 MPG after such a coast. I could start a timer once the AVG MPG dropped to 40 MPG and stop it when it dropped to 20 MPG. If it takes twice as long to drop from 40 to 20 in "N" than it did in "D", then I would guess that it is twice as efficient.
09-14-06, 10:23 PM
#40
Tech Info Resource
iTrader: (2)
I have tried this on every Toyota I've owned (event the Scion) and they all shut off the fuel on decel until about 1200 rpm on manuals, or in this case, the book says 1000 rpm for this automatic. I never really bothered to check the wife's auto Scion tC.
09-14-06, 10:24 PM
#41
I'm not saying you are lying about the 27 MPG. What I meant is that your cousin must not be driving it hard. If you looked at my guage right now, it says 24.2 MPG. Of course, I'm driving it like Tinker Bell. If I took my car to a track, I'm confident I could average under 10 MPG for the whole tank.
09-14-06, 10:26 PM
#42
Tech Info Resource
iTrader: (2)
I'm trying to derive a test to see how much more fuel efficient it is to idle in "N" than it is in "D". The only idea I can come up with is to reset the "AVG MPG" at the same moment I'm doing a high rate of speed on the highway (ie. 100 MPH) and engine brake to nearly a stop. Once I'm at a stop, the AVG MPG would be really high, but would drop quickly. I imagine that the AVG MPG would be well over 50 MPG after such a coast. I could start a timer once the AVG MPG dropped to 40 MPG and stop it when it dropped to 20 MPG. If it takes twice as long to drop from 40 to 20 in "N" than it did in "D", then I would guess that it is twice as efficient.
09-14-06, 10:29 PM
#43
Lexus Champion
I think putting your transmission into N will allow it to cool, mine always seems to be very hot. A cooler transmission is under more stress.
It's all good, I'm just asking, so do you guys trying to hit a higher fuel economy goal, do you also do other things that are proven to improve gas mileage like frequently check tire pressure, making sure you engine is well-tuned, use different oil/gas to see which gives you the best gas mileage, remove excessive weight from car maybe even the spare, fill your tank early in the morning or late in the evening, roll up your windows on the highway to reduce drag, draft big trucks on the highway, accelerate before you approach a hill...not ON the hill, illegally throw the car into N to coast down big hills, time your drive thru the stoplights so you don't have to idle, park your car so you can drive out instead of using gas going into reverse, and/or other things I read on "how to increase your gas mileage?"
It's all good, I'm just asking, so do you guys trying to hit a higher fuel economy goal, do you also do other things that are proven to improve gas mileage like frequently check tire pressure, making sure you engine is well-tuned, use different oil/gas to see which gives you the best gas mileage, remove excessive weight from car maybe even the spare, fill your tank early in the morning or late in the evening, roll up your windows on the highway to reduce drag, draft big trucks on the highway, accelerate before you approach a hill...not ON the hill, illegally throw the car into N to coast down big hills, time your drive thru the stoplights so you don't have to idle, park your car so you can drive out instead of using gas going into reverse, and/or other things I read on "how to increase your gas mileage?"
09-14-06, 10:32 PM
#44
Not claiming to be the expert, I can take a stab at this. If there was no N, how would you tow a disabled vehicle or how would you move (push) an automatic if the engine will not start?
When you tow a vehicle, you need to put the car in D first, then in N. You shouldn't go from R to N.
R is next to P because from P when you want to back up your car, you don't want to go into D first.
As far as design, I wasn't around when they were designing the gear sequence, it could have been something as simple as there was no Park, only R, N, and D and so no obstruction any place except when going into reverse. I dunno. But I think neutral was where you started cars that didn't have a Park.
When you tow a vehicle, you need to put the car in D first, then in N. You shouldn't go from R to N.
R is next to P because from P when you want to back up your car, you don't want to go into D first.
As far as design, I wasn't around when they were designing the gear sequence, it could have been something as simple as there was no Park, only R, N, and D and so no obstruction any place except when going into reverse. I dunno. But I think neutral was where you started cars that didn't have a Park.
Generally, a RWD car should be towed from the rear (rolling on the fronts). I've never heard of the requirement to put it in D before N instead of R when towing. I'm not disagreeing, but I've never heard of it.
Regarding the obstruction, all of the column shift automatics I've driven would easily bump from D to N and back without pulling the lever toward you, but all other gear positions required a lever pull. Similarly, the lever would easily bump from "1" to "2", and "2" to "D", and "D" to "OD" without a pull, but it would not bump down without a pull. I always figured there was a reason behind the design.
09-14-06, 10:46 PM
#45
If you really want to test this, you need to coast downhill in neutral. It will tell you right away which is better. My bet is, you'll be in fuel cut on decel in gear, and actually using more fuel idling in neutral, so it won't be a fair comparison between idling in D or idling in N. Is there fuel flow data on the CAN bus? That would answer the question definitively within the allowable error for the measuring devices.