how to drive for best mileage

[harriw]

Hey folks,

I know I'm digging up an old argument here, but I've done the searches, read what I can, and am still a bit confused.

From what I've read, the 4.0L makes peak torque around 2400rpm, which means you should get your best mileage about there, right?

I've also read things like "short shift to keep your rpm's down" in Jim's "how to" for best gas mileage. So... what should I do? Try to stay as close to 2400rpms as possible, or try to keep the rpm's down as much as possible (without lugging)? Obviously you can't always hit 2400 on the head - are you better off keeping a lower gear and spinning the 4.0 up a bit higher, or are you better off shifting up? When climbing gears, should you shift right at 2400, or try to keep 2400 your average, shifting closer to 3000 or so?

Obviously there's a lot of other factors such as the slope you're on, how fast you need/want to get up to speed, etc., but I'm looking for some simple guidance. Is there a site anywhere someone can recommend that might give a sort of high level overview of this engine, such as torque curves, recommended shift points (for a manual), etc.?

What do you folks use as a rough ROT for shift points (for 5spds) - when you're trying to sip gas, not spin the tires. By the way, this is a '94 4x4 with the L/S rear and 3.73 gears. On the expressway, about 72-73mph in 5th seems to put me at 2400rpm.

Thanks guys.

-Bill

 

[LittleHorse]

There are so many variables with this that it's impossible to accurately predict. First, the TQ peak is only the most efficient point if you're comparing the RPM range at full load. What you want to look at is a BSFC map for the engine - Brake Specific Fuel Consumption. It's usually expressed in g/kWh, as in how many grams of fuel it takes to produce 1 kJ of energy per second for an hour. It's usually plotted with BMEP (brake mean effective pressure) on the y axis and engine speed on the x axis. BMEP is basically an expression of engine load - so there's a specific % of full load and a specific engine speed at which the engine is most efficient, and it's not necessarily at the tq peak but usually it's close, and usually its at a lower RPM.

Ideally you would operate at that one point during all acceleration, but you can't do that with a transmission operating with discreet ratios, which is the idea behind a CVT.

Since most cars don't have a CVT, the next best thing is to try to keep it as close as possible. More throttle at an RPM below the torque peak is almost always more efficient than less throttle above the tq peak, so giving 60-70% throttle and shifting at the tq peak will USUALLY be the best option.

Check out this page
http://mark.tranchant.co.uk/2008/06/driving-more-economically

and skip down to "tip 2", since tip 1 is kindof a no brainer. it has a couple example BSFC charts and does a decent job of telling the story.

 

[cr_the_machinist]

I keep my rpm's under 3000 and try not to go over 2500. I just let the transmission do the work and not the engine when it comes to gaining speed from a stop. It's cold in Michigan right now so it doesn't matter how easy you take it, you still wont break 15.5 mpg in a 4.0ohv 4x4. Driving like a grandma doesn't help too much in a 4.0. I think the most i've gotten out of a tank so far is 290~ish miles on a 17 gallon tank. I just get it up to 2500 and let the torque converter do its job. Once it locks up I'll stick to 1500 rpm and that will send me at a good 50~52 mph. The trick is to get your torque converter to lock up asap, than you not wasting anymore enengy through the converter.

 

[wahlstrom1]

Full throttle to 25-2800 Rpm and grab gears quick for best city accleration while maintaining decent fuel economy. You can idle your way through the rev range for the best fuel economy but it tends to piss other drivers off.

-andrew

 

[bobbywalter]

i get my best milage riding a pedal bike, its much faster then walking.

 

[bobbywalter]

on a serious note my best milage is @ 17-1800 rpm. unfortunatly that is also 55 mph

currently with winter fuel it varies from 18-25 mpg on my commuter loop.. but i think the shitty injectors are as at fault as the winter diesel with the wild variations..i cleaned the tank and only been running reg wnter #2 and 911 per recommendations the last 3 tanks.



the variance is just crazy...


but it beats the fawk out of 9-12 mpg

 

['93BajaSport]

For the basics, avoid frequent starts/stops/slowing/accelerating, reduce aerodynamic drag if practical(like roof racks), and use the cruise control on flat ground to avoid any erratic throttle changes.

One thing that does not help is going down hill in neutral. Aside from being illegal, I think just about all auto manufacturers these days employ "overrun fuel cut" in their EFI algorithms. What it does is shut the injectors off completely when the throttle is shut and the rpm is above a certain point, such as engine braking down a grade.

My '93's mileage has not varied much since it was new, which was 231,000 miles ago. I think back then it averaged 19-21 in mixed driving and could manage 24-25 if the whole tank was burned up on the highway. Now it's more like 18-20 average, but it needs some attention like new O2 sensors. My Toyota truck gets 28 in mixed driving and 31 on the open road.

 

[LittleHorse]

Full throttle to 25-2800 Rpm and grab gears quick for best city accleration while maintaining decent fuel economy.

should do pretty well, though about 3/4 throttle would be the best.

You can idle your way through the rev range for the best fuel economy but it tends to piss other drivers off.

-andrew

eh, not really true. The engine is LEAST efficient at low load - meaning it's doing the least amount of work for the most amount of fuel. Nursing the throttle during accel is the worst thing you can do for fuel economy.

 

[Stranger ranger]

buy a 4cyl car

 

[wahlstrom1]

should do pretty well, though about 3/4 throttle would be the best.



eh, not really true. The engine is LEAST efficient at low load - meaning it's doing the least amount of work for the most amount of fuel. Nursing the throttle during accel is the worst thing you can do for fuel economy.

Ya, should have said a little less then full throttle. I found as long as you don't wind it out through the rev range and watch lights to avoid stop/start events will help get the best mileage. Also lugging around at low rpm doesn't seem to help either, my truck seems to sit happily in town around 24-2800 rpm.

-andrew

 

[Rob06]

I did the short shift easy on the go pedal and got 21 MPG

I just filled it tonight and this time I didnt short shift it - I let it spin up to 2500-2800 before shifting and never let the RPM go below 2k and I got 21mpg....

The 4.0L is a short stroke and short stroke motors dont like to be run low in the RPM range. My 4.0L doesnt make any power below 2k. My 3.0L pulled MUCH better than the 4.0L at 1500 RPM.......

Rob

 

['93BajaSport]

Short stroke? The 5.0 V8 has a shorter stroke than the 4.0 V6.

My 4.0L has proven itself in rocky offroad sections down to idle rpm. Even I was surprised.

 

[Hahnsb2]

I get about 1.75 MPG better if I keep my X 4.0 above 2K, so no 5th gear till about 60-65. I average almost 18MPG mixed, on a 250 mile freeway trip I got nearly 20MPG cruising 75 (about 2400 RPMs), if I dropped to 65 I'd get over 20 easy.

 

[quinnGoes]

what about in an automatic?

it can't be most gas efficient to drive around town putting 3/4 throttle down out of every stop..

 

[RumpRanger98]

what about in an automatic?

it can't be most gas efficient to drive around town putting 3/4 throttle down out of every stop..

What you just said there proves its how you drive, how you get the MPG. if your putting 3/4 throttle down at a red to green light, then right there your wasting gas. I give 75% throttle myself, but honestly, your driving habit, + your vehicles condition, = your mpg.


automatics ...automatically get 1-3mpg less on any car. the best way to get the best mpg on an automatic, besides having the vehicle up to date on tune up etc. is to drive like your 101 years old, people will honk but it wil shift at low rpms