Enhancing 4runner power mpg
05-24-2012, 03:10 PM
#21
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Sort of, but not really: The only time that applies is if you have an auto trans, in which case the engine is still not working as hard, thus lowering your injector pulse width. The pulse width is determined by an equation called "calculated load", not rpm. If you have a manual, speed and gearing are constants which do not change in the MPG equation--obviously if you go down a hill with a manual, the rpm's do not drop. Automatics are a different story, unfortunately for automatic owners, the losses from downshifting to go up a hill cancel out any gains derived from upshifting going down a hill. It is a net zero in both cases because we are testing at a constant speed. You cannot maintain said speed unless the injectors deliver X fuel per second to create Y horsepower.
When MPG tests are done in real life, they are done by using a flowmeter which determines EXACTLY how much fuel flows to the engine per second at a specific speed under specific conditions. It doesn't matter what the engine is doing to maintain that speed, it could be 100 rpm or 135,000 rpm, both cases are irrelevant as long as the amount of fuel flowing per second can be measured with the car maintaining a constant speed.
When MPG tests are done in real life, they are done by using a flowmeter which determines EXACTLY how much fuel flows to the engine per second at a specific speed under specific conditions. It doesn't matter what the engine is doing to maintain that speed, it could be 100 rpm or 135,000 rpm, both cases are irrelevant as long as the amount of fuel flowing per second can be measured with the car maintaining a constant speed.
The MPG test and actual miles per gallon were not being compared so I don't see the need to bring up "Factory Testing" methods. RPM's Directly effect the ammount of fuel dumped to each cyl. because it directly effects the cycle of the injector, regardless of the amount of fuel being used...
LMAO, couldn't have said it any better. Though I think if MPG was an issue and I still wanted the truck, I would save the money and grab a 3.4 to swap in.
Last edited by Vudujoose; 05-24-2012 at 03:13 PM.
05-24-2012, 09:35 PM
#22
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^I'm sorry, what?!
If I let off the gas, going downhill, in my MANUAL 4runner, leaving it in gear... engine speed will increase or decrease based on whether or not engine braking can overcome acceleration imparted by gravity. Unless you use the clutch, the engine will turn at a given speed relative to the wheels' given speed, determined by gearing.
If I let off the gas, the ECU knows the throttle is closed, engine braking will occur as the ECU stops fuel delivery. The wheels are now turning the engine over. This uses zero fuel, but does slow the vehicle some (the engine is a source of drag on the drivetrain). Automatic transmissions may or may not shift to neutral going downhill.
The point of this is... engine load dictates fuel injection management. Engine speed has an effect (generally, the ECU knows higher rpms demand richer fuel/air ratios) but is not the final say on injector pulse duration.
I'd love to see your manual truck stay in gear, maintain speed, and LOSE engine speed all at the same time. Your clutch must be toast if that's the case.
If I let off the gas, going downhill, in my MANUAL 4runner, leaving it in gear... engine speed will increase or decrease based on whether or not engine braking can overcome acceleration imparted by gravity. Unless you use the clutch, the engine will turn at a given speed relative to the wheels' given speed, determined by gearing.
If I let off the gas, the ECU knows the throttle is closed, engine braking will occur as the ECU stops fuel delivery. The wheels are now turning the engine over. This uses zero fuel, but does slow the vehicle some (the engine is a source of drag on the drivetrain). Automatic transmissions may or may not shift to neutral going downhill.
The point of this is... engine load dictates fuel injection management. Engine speed has an effect (generally, the ECU knows higher rpms demand richer fuel/air ratios) but is not the final say on injector pulse duration.
I'd love to see your manual truck stay in gear, maintain speed, and LOSE engine speed all at the same time. Your clutch must be toast if that's the case.
05-24-2012, 10:47 PM
#23
Registered User
^I'm sorry, what?!
If I let off the gas, going downhill, in my MANUAL 4runner, leaving it in gear... engine speed will increase or decrease based on whether or not engine braking can overcome acceleration imparted by gravity. Unless you use the clutch, the engine will turn at a given speed relative to the wheels' given speed, determined by gearing.
If I let off the gas, the ECU knows the throttle is closed, engine braking will occur as the ECU stops fuel delivery. The wheels are now turning the engine over. This uses zero fuel, but does slow the vehicle some (the engine is a source of drag on the drivetrain). Automatic transmissions may or may not shift to neutral going downhill.
The point of this is... engine load dictates fuel injection management. Engine speed has an effect (generally, the ECU knows higher rpms demand richer fuel/air ratios) but is not the final say on injector pulse duration.
I'd love to see your manual truck stay in gear, maintain speed, and LOSE engine speed all at the same time. Your clutch must be toast if that's the case.
If I let off the gas, going downhill, in my MANUAL 4runner, leaving it in gear... engine speed will increase or decrease based on whether or not engine braking can overcome acceleration imparted by gravity. Unless you use the clutch, the engine will turn at a given speed relative to the wheels' given speed, determined by gearing.
If I let off the gas, the ECU knows the throttle is closed, engine braking will occur as the ECU stops fuel delivery. The wheels are now turning the engine over. This uses zero fuel, but does slow the vehicle some (the engine is a source of drag on the drivetrain). Automatic transmissions may or may not shift to neutral going downhill.
The point of this is... engine load dictates fuel injection management. Engine speed has an effect (generally, the ECU knows higher rpms demand richer fuel/air ratios) but is not the final say on injector pulse duration.
I'd love to see your manual truck stay in gear, maintain speed, and LOSE engine speed all at the same time. Your clutch must be toast if that's the case.
LOL I guess you drive around in 4th gear down hills? Is this the new Jake style brake system for small trucks?
I drive a car that tells me when I'm under load every day, how do I know it's under load you ask, the spooling sound it makes as I labor the engine. Oddly enough when going down hill this very afternoon I tested your theory just wondering if maybe I was wrong. I run at about 2600RPM's in 5th gear on a flat surface at 60Mph, yet going down hill I was gaining speed at 2000RPM's and as I went up the hill I was getting into boost at 3000RPMS.
Dunno what to tell ya on that one...
Regardless of how you look at it, RPM's effect MPG, I never said pulse wasn't a factor, as a matter of fact I agreed with you, but you disagreed that RPM's had anything to do with MPG and that just flat out wrong. That's like saying your brain doesn't effect your heart and lungs.
PS. Engine load with no throttle is just that engine load. The ECU doesn't dump more fuel on an engine that's not pulling in air. AFM's / MAF's have a purpose and I'm pretty sure that's it.
Last edited by Vudujoose; 05-24-2012 at 10:49 PM.
05-25-2012, 05:18 AM
#24
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I almost think we are not talking about the same set up. While I may not have a jake brake on my 4runner, letting off the gas going down hill will keep my speed constant on most hills.
I did not say that rpm had NOTHING to do with mpg. I say engine speed had much less say in what was happening to injector pulse duration. Obviously faster moving parts require more energy to keep them in motion.
I'm wondering if we aren't speaking clearly here? I simply cannot see how you are saying, in a manual vehicle, engine speed can change while vehicle speed remains constant, given that you're in gear and off the clutch. Regardless of the grade of the hill you are on. I will give you that smaller engines and/or less resistive engines won't do anything to slow your acceleration down a hill. My 3vze has a fairly aggressive fuel cut, and makes decent vacuum... so DOES supply decent engine braking. Which uses no fuel, regardless of engine speed.
Where do we stand? :s
I did not say that rpm had NOTHING to do with mpg. I say engine speed had much less say in what was happening to injector pulse duration. Obviously faster moving parts require more energy to keep them in motion.
I'm wondering if we aren't speaking clearly here? I simply cannot see how you are saying, in a manual vehicle, engine speed can change while vehicle speed remains constant, given that you're in gear and off the clutch. Regardless of the grade of the hill you are on. I will give you that smaller engines and/or less resistive engines won't do anything to slow your acceleration down a hill. My 3vze has a fairly aggressive fuel cut, and makes decent vacuum... so DOES supply decent engine braking. Which uses no fuel, regardless of engine speed.
Where do we stand? :s
05-25-2012, 11:48 AM
#25
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One way is to put the trans in neutral, jack up one of the rear tires, and turn it one whole turn, and count the number of turns the driveshaft makes... then divide that by two since the other rear tire is on the ground.
If the driveshaft turns exacly 8 times for every on turn of one wheel (provided the other tire doesn't move) you have a 4:1 rear end (8/2:1).
If it turns 8.5 turns, (8.5/2:1)= 4.25:1.
Making sense?
If the driveshaft turns exacly 8 times for every on turn of one wheel (provided the other tire doesn't move) you have a 4:1 rear end (8/2:1).
If it turns 8.5 turns, (8.5/2:1)= 4.25:1.
Making sense?
10-02-2014, 02:25 PM
#26
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25mpg!?!?!
I find it odd that the vehicle came with 3.90:1 gears. Is that from the factory?
I think the best combination is the typical 4.10:1 gears (manual) 4.30:1 gears (auto) with the stock tire size from the factory (225-75R15 i believe).
Be aware that changing gear ratio means the speedo is out of calibration and that will effect your MPG unless you compensate in your calculations at each refuel.
My 91 truck from the factory was getting almost 25MPG with 4.10:1gears/manual trans/stock tires. Moved up to 32x11.50 ATs and lost ~ 3MPG (after corrections to the calculations due to speedo calibration) When I stepped up to 38.5x16 swampers and regeared to 5.29:1, my mileage was down to 18MPG (and this tire/gear combo corrected the offset in the speedo to almost perfect - within 1% accuracy)
The trick is to keep the engine within its optimal power band. Having the engine struggle because its running too low an RPM range or racing because it is running too high an RPM range will hurt fuel economy. Oh and you can hurt mileage running high RPMs since the computer likes to keep the engine at an optimal air/fuel ratio. More air means more fuel consumption. going downhill with your foot out of the skinny pedal means the throttle is closed more meaning less air. the opposite hold true for uphill.
I think the best combination is the typical 4.10:1 gears (manual) 4.30:1 gears (auto) with the stock tire size from the factory (225-75R15 i believe).
Be aware that changing gear ratio means the speedo is out of calibration and that will effect your MPG unless you compensate in your calculations at each refuel.
My 91 truck from the factory was getting almost 25MPG with 4.10:1gears/manual trans/stock tires. Moved up to 32x11.50 ATs and lost ~ 3MPG (after corrections to the calculations due to speedo calibration) When I stepped up to 38.5x16 swampers and regeared to 5.29:1, my mileage was down to 18MPG (and this tire/gear combo corrected the offset in the speedo to almost perfect - within 1% accuracy)
The trick is to keep the engine within its optimal power band. Having the engine struggle because its running too low an RPM range or racing because it is running too high an RPM range will hurt fuel economy. Oh and you can hurt mileage running high RPMs since the computer likes to keep the engine at an optimal air/fuel ratio. More air means more fuel consumption. going downhill with your foot out of the skinny pedal means the throttle is closed more meaning less air. the opposite hold true for uphill.
I get 250kms to a tank :s
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