hhn2002

i hate the way my car eats gas, so in your opinion what do you think would be the most efficient driving manner conducive to the least fuel consumption? ergo shifting rpm and throttle positions and also if that should change going into a different gear(shifting characteristics of going into 2nd vs. going into 5th).
thanks.

t24todd

iTrader: (7)

shift when you shift light comes on or 2,500 if you dont have one...coast in nuetral coming to stop lights, stop signs etc...no jack rabbit starts..besides that its a rx7 not a prius.

SureShot

The basics:
Short shift - change gears below 3K.
Use the throttle like there was an egg on it.
When cruising, keep an even speed so the ECU can stay in closed loop with the O2 sensor.
Stay in gear when decelerating. The ECU cuts fuel & just pumps air down to 1500 RPM.

SureShot

I disagree here.
When coasting in neutral the engine still needs fuel to idle.
It you're still in the gear you were cruising at, the ECU cuts fuel altogether while decelerating.

If you want you can down shift as the tach nears 1500.

-Bill

Black91n/a

Sit in it with the engine off and make engine noises. Take the bus, walk, ride a bike. Although technically this isn't driving and you don't get any miles from your not having the engine on it is more economical.

Seriously though, just drive as gingerly as you can. Always cruise in the highest gear that you can, coast down hills in neutral accelerate slowly and evenly, maintain speed as much as possible. Use the brakes as little as possible, don't slow down more than you have to for corners, if you can, if you see a red light ahead slow down and try to time it right so that you arrive at the lights when they change to green, that means less time accelerating for less fuel burned. Also, just drive slower. If you're on the freeway, instead of speeding at 70, 80 or whatever, stick to the speed limit, that'll help lower your fuel consumption.

Either that or you could enjoy the drive and to hell with the fuel bill.

ericgrau

iTrader: (1)

Search forums, asked before. Shift at shift light, avoid unnecessary braking, keep your speed (mph) down. Having a lead foot does NOT hurt mpg, unless you also drive at a high mph or brake excessively. Higher throttle actually helps. That's what makes hybrids and smaller engines so efficient. Because they need high throttle just for normal driving. Though this kind of driving in a sports car may lead to some practicality issues. I'm just saying there's no reason to grandma it.

hhn2002

actually today driving back and forth to school today 15min drive each way twice today and i noticed that using as little throttle as possible(keeping the secondary throttle plates closed) seemed to not help at all and i feel pretty certain almost made it even worse. eric so whats the theory on high throttle usage being beneficial for smaller displacement engines or where'd you hear it from bc i've never heard of that b4. actually my theory is keep a somewhat light throttle but not too light and shift at 4k where the power would start to starve off with the semi light throttle which in turn might help with air turbulence and help it stay more lean. since the leaner the more fuel efficient. is this making any sense to anyone? lol what do you guys think? either way i dont i want to go that light again.

scathcart

Incorrect.
Engines under high load acceleration require more fuel compared to those accelerating under low load. Engines operating at higher rpm also have higher frictional and heat losses. Heavy acceleration WILL burn significantly more fuel.

This is easy to see with a fuel flowmeter on a returnless fuel line system, on cars so equipped.

anewconvert

iTrader: (1)

You get the best mileage while cruising. The idea behind higher throttle input is that you get to your cruising speed as fast as possible, and stay there. Accelerating slowly just means that you spend more time getting to your eventual speed, and on the street that could mean you spend almost the entire time accelerating before you slow down for a light.


As for neutral v engine braking, neutral uses gas to idle. Idling is an inefficient process. Engine braking uses no fuel to keep the engine moving, just the momentum of the car transfered through the transmission. Keep it in gear until you feel the car jerk forward, then downshift


BC

anewconvert

iTrader: (1)

I suppose we need to define 'heavy' throttle. Getting the car out of closed loop is not a good idea for gas mileage, particularly on a stock ECU. I am an advocate of getting to cruising speed as quickly as possible within reason. WOT to cruise is a waste of gas, but so is shifting so early that you spend the better part of a mile getting to cruise speed. There is a happy medium.


BC

SpeedOfLife

iTrader: (16)

But that would be more efficient then only taking a 1/4 mile to get up to speed, especially since you can still accelerate from most speeds (probably at least everything from 0-80mph) while in closed loop.

ericgrau

iTrader: (1)

Your efficiency is much higher under higher throttle. Much more acceleration per gallon. Even though you use more fuel per second, it takes much less fuel to get up to speed. A common technique during mpg competitions is "burn and coast". You go WOT up to speed, go into neutral until you slow down a bit, then WOT again. Not that I'd do that on the freeway.

It takes very little throttle to take you out of closed loop. When you are accelerating you are almost never in closed loop. Closed loop adds about 2mpg, btw.

So I'm saying the most practical way to save gas is to accelerate up to a low speed at whatever throttle you like, shift at the shift light, then cruise at constant throttle. Leave plenty of space between you and the guy in front of you (so there's no need to brake), and coast when you know a stop is coming (so you brake less). It is difficult for me to lose more than 1-2 mpg no matter how hard I drive... and I have quite a bit of fun.

Btw I don't go 60mph on the freeway even though it saves gas. There's a balance between time and mpg. In the city or in traffic OTOH, there's usually little benefit from speed. You can't go faster than everyone else, even if you pass a couple cars (omg 2 seconds saved!), and it only forces you to brake more.

RYS13

Possible stupid question but why does turning harder consume more fuel than turning normally?

SpeedOfLife

iTrader: (16)

I really should shut up about open and closed loop, as I can't remember which means which thing... But if the car can get better mileage by using the O2 sensor, why wasn't it set up to use it all the time? I assumed that whichever loop doesn't use the O2 sensor must be pretuned for efficiency, but maybe that's incorrect.

scathcart

The stock oxygen sensor is only accurate at 14.7:1 air-fuel ratio. Your engine cannot run at this AFR all of the time, it needs more fuel to maintain a steady idle, make power, and prevent detonation. Only under very light loads above idle, such as cruising, will then engine operate well at this stoichiometric value.

When the engine is in closed loop, the oxygen sensor is directly altering the fuel injected into the engine. Think of it as an actual closed loop: the oxygen sensor tells the ECU how much fuel to add or subtract, which in turn affects the oxygen sensor reading. In open loop, such as idle or any acceleration, the oxygen sensor is ignored, since it is not accurate under those driving conditions.

A wideband oxygen sensor can be set up to run closed loop all the time. Most of the Auto-tune features of some aftermarket ECU's are a closed loop design, where the user inputs the desired AFR for the type of driving condition, and the wideband directly changes the fuel map based on its reading.

SpeedOfLife

iTrader: (16)

If that's the case, why does my A/F gauge still show a reading when accelerating and at idle? It doesn't show a reading once I've been cruising, and I've had my ECU code lights hooked up while driving and the O2 code only comes up when the gauge doesn't show any reading. Additionally, I have noticed a slight stumble when it transitions to open loop mode. Any idea why? Because of the extra fuel it doesn't actually need?

I just bought an SAFC 2, and I want to use it not just for power gains, but to enhance fuel economy, does anyone know if a wideband O2 sensor would be the next thing to help with better performance and mileage?

st1llet0

iTrader: (2)

Tips on fuel economy can be found in the owners manual. It's actually pretty detailed. Reduce speed in strong headwinds, keep tires properly inflated, reduce speed on bumpy roads or slippery roads, all that jazz.

SpeedOfLife

iTrader: (16)

I feel that the question went deeper than those, but for posterity I guess it's good to have the basics up there.

scathcart

Your gauge still shows a reading because the sensor is still putting out a signal. The narrowband oxygen sensor can tell you exactly when you're at stoichiometric AFR's, or running leaner or richer than that, but not by exactly how much. Its not that it doesn't give you a reading, its that the reading is not accurate.

For your code problem, check the O2 sensor wiring, or more likely, a faulty or low quality sensor. Nothing on the gauge and the code popping up means no oxygen sensor signal.

Yes, you can tune your S-AFC for better fuel economy. While a wideband isn't capable of directly controlling the S-AFC (such as an auto-tune function), it is an invaluable tool for tuning. Under cruise, you can disconnect the oxygen sensor completely and then pull at fuel in the light throttle map until the car just begins to buck, and then add a little fuel back in. This will typically put you leaner than stoichiometric, around 15.5-15.8:1. Under WOT, you will need to determine a safe AFR to tune to based on your set-up.
By tuning leaner than stock and not allowing the engine into closed loop, you can typically achieve 25+ mpg under highway cruising.

SpeedOfLife

iTrader: (16)

I understand that, but it is interesting that the gauge can hold at just about any point on its dial given the right circumstances. Maybe because of the way different temperatures act on the sensor?

I know it means no signal, but I wasn't sure if that was because the sensor cuts out from cooling or what the deal is. It only happens when all these conditions are met:
-I haven't been accelerating for at least a little while
-I'm not idling
-Lower RPM, probably below about 3500. I'll have to keep a closer eye to see exactly where (RPM) it will occur.

The sensor is very new, but was fairly cheap.

How do you not allow the engine into closed loop after you've tuned and reconnected the O2 sensor? Obviously (to me) the O2 sensor reading should be used as one of many flags in case dangerous conditions occur, but since it's still hooked to the system I wonder how you'd keep achieve that.

scathcart

Sensor overheating will definitely affect the reading. So will it being too cold, though that's rarely an issue on rotaries.

I leave it unplugged and monitor with a wideband. They're cheap enough these days to leave in the car. The car doesn't care if the sensor is disconnected. the ECU only uses it under cruise, and if it doesn't get a signal, it reverts back to open loop and uses the fuel map anyway.

Havoc

Ive see one guy 750km to a tank with a haltech E8 (wideband) with closed loop. LOL Im lucky if I was getting 250km.

But hell if I wanted fuel efficiency why would I want a rotary ?

SpeedOfLife

iTrader: (16)

Are there circumstances under which using the preset fuel map would be less desirable? As in, any time where closed loop actually helps you in terms of power or fuel economy? If not, why is the system there?

SpooledupRacing

You drive and RX7 if you dont like the mileage you are getting buy a honda...

/THREAD!

tomoaac

If you look at brake specific fuel comsumption charts ( Only seen them for piston engines). The lowest fuel usage for work out is at 90% load around the 2800rpm range.

And after 3000rpm the fuel usage goes alot!!

Therefore forget about being gentle on the throttle, just change up before 3000rpm. (maybe a bit higher for rotary).