Improve Gas MPG...?

[scott slade]

Just returned from a great trip to the Mojave Desert, and some awesome trails.  Did not buy my 05 TJ Unlimited six speed for the great mileage...!!   but there has to be some way to get a few more yards out of a tank..?   What is the best result for the buck...?  Any thoughts...?  Thanks...

[parabs]

buy tires with a low rolling resistance...something like a toyo open country h/t.

I dont know what kind of tires you have on your jeep, but usually a/t's deliver decent mileage while providing decent traction and decent off road ability, they are lighter than mud tires generally, I think you can sum up an A/T tire as a jack of all trades, master of none.

[scott slade]

Rolling on 31 inch BFG AT's....  Always been a good tire for the trails I do, and on the road...  I thought...   Wondering about an after market air intake..?   

[FiEND]

if there were any addons that could increase fuel economy, the manufacturer would have put them on.  they really do know how to build vehicles.  addons may increase power or noise or ability, but they all end up losing in fuel economy.

unless you want to put some aerodynamic addons

post your fuel economy or do a search, there's lots of posts to compare with.

[tubby]

You're right.I don't think people purchase Jeeps with fuel economy on their mind. That's what hybrids and Honda Civics are for. Your TJ has the aerodynamics of a brick. Forget little doo-dads that may or may not increase fuel economy, and adjust your driving techniques. No jack rabbit starts, don't carry excessive amounts of weight in the vehicle.

Give it a shot. It won't cost you anything to make small adjustments to your driving.

[Slewfoot]

Just a thought, but an electric rad. fan might help...though some may debate the off-road reliability of them.

[parabs]

if there were any addons that could increase fuel economy, the manufacturer would have put them on.  they really do know how to build vehicles.  addons may increase power or noise or ability, but they all end up losing in fuel economy.

unless you want to put some aerodynamic addons

post your fuel economy or do a search, there's lots of posts to compare with.

I disagree with this general statement....so if you will follow me on my fairy-tail scenario..

Fact:  When I work near/at Fort Mac, I get noticeably better fuel economy then around Calgary.  Fort Mac is also quite hilly, perhaps not as hilly as Calgary, but it is definitely not a flat landscape.  Calgary Airport is 3553 ft above sea level.  Fort McMurray is 1214 ft above sea level. 

Theory:  I have read that for every 1000 ft increase in elevation you loose ~10% of your power.  A 200 hp engine will lose 20hp at 1000ft, and additional 18 hp at 2000ft, another 16hp at 3000ft, and another 7 hp at 3500 ft.  In Calgary, a 200 hp engine makes ~139hp, but that same engine in fort mac makes ~180hp

Jeeps are severely underpowered, no one will argue that, however if you add forced induction (enter fairy-tale land) you first somewhat negate the 10% loss per 1000 ft as you are now pressurizing the engine, plus you add over and above.  A normally aspirated engine is much more efficient at sea level vs higher elevations.

The stock 4.0l powerplant is starved of air in the Calgary area.  If you supercharged/turbocharged your engine, you would see gains in mileage, provided you maintained your driving style, i.e, a hill you drive up at WOT and can only maintain 45mph, that same vehicle with double the power will pull that same hill at 45mpg burning much less fuel as it is working at a much lower rate of work..

Perhaps thats not a good way of explaining it.  It was explained to me once like this, if you have a box that weighs 25kg, you as an 18 year old could carry that load much more comfortably and likely haul that load further than yourself as a 13 year old (unless you're benjamin button) because you are a much more powerful person.

Theory End.

The problem with my argument is there are not a lot of blown jeeps in Calgary (that I know of anyways) to compare.

[FiEND]

they shouldn't be starved of air.  there is a air-fuel mixture that the computers regulate.  if you add more air you also have to add more fuel right?

more air + more fuel = more fuel

the 18 year old needs more calories than the 13 year old.

[Pookapotamus]

you are kind of right al, but the 4.oL does not have a mass airflow sensor, they were calibrated at the factory to flow a certain amount of air, but air pressure does affect this. the factory just set these engines up to run under most circumstances, there are a lot of things that can be done to change their running characteristics but unfortunately if you are pre 96 (obd1 systems) they are hard to change. for instance i am running a 2001 intake on my 95 to improve airflow, but this is not really being used to its full potential because the engine management system does not know that it is now able to ingest more air. it did give me some improvements but untill i update my system to an obd2 and play with timing and injector pulse i will not use that intake to its fullest potential. therefore my gas milage sucks!

adding things like electric fans does change the gas milage but they are very marginal as the aerodynamics of any jeep is like said before a brick. little things like tire pressure or low rolling resistance plays a part too but just dont expect to gain much with little changes.

imho go ahead and change things and see what works for you, every jeep is different, what works on one might not work on another. but hey give it a try and share your results with others!

Pook

[JackstandJohnny]

put a slip tank in the back, then you'll go a lot farther on a fillup...................  what mileage did you get?  should probably include that.  if its over 400K/tank you're getting GOOD mileage.



must be nice to own a jeep that you are conerned with a couple MPG instead of it 'making it to the destination' 

thast what some of us worry about

[Evil-Jeep]

Here is what I have done. Added a cone filter, changed the plugs to e3s, and added a taurus fan.

I spent around $200 for all upgrades. (I still need to build a better heat shield for the filter so maybe $250 whendone)

I have noticed better mileage/ and power than before; however, I changed the plugsbecause the old ones were fouled, I changed the filter because the old paper was full of dirt and the fan got changed when it was seized.

So to go from what it was to is now was a huge improvement, I did however notice the largest gains with the filter change than anything else, and the way I see it is this, even if you only save 5% per tank it will pay for it self by the end of the year or sooner.

my only caution would be to not invest large amounts for a small return as an example, I probably did not need to spend $75 on plugs for a 3.25% gain when I could have spent $30 for a pair that would given a 3% gain.

Other than check tranny, transfer, engine and diff oils, I noticed the biggest gains after having everything flushed and changed.

[Bnine]

imho go ahead and change things and see what works for you, every jeep is different, what works on one might not work on another. but hey give it a try and share your results with others!

Pook

Do you know what the term "every jeep is different" stands for.

"Most folks dont understand how jeeps work so they use the above term in an effort to generalize what they dont understand"

Anyone care to poll what 4 cyclinder jeeps get for milage on average compared to 6 cylinder jeeps?

Save yourself the trouble, they are nearly identical.

It doesnt matter what you do. The energy required to move the amount mass that is a jeep only changes marginally from jeep to jeep, based on slight variations in shape and weights.

No matter how much you screw with the old motors, you can only make them so efficient, which like Al said, after 50 some years the dealer got pretty good at.

A well maintained xj gets 14-20mpg depending on the driver. A well maintained wrangler gets 12-17mpg depending on the driver.

The difference? A bit of aero dynamics and 1000 lbs.

Do your mods because you want your mods. Modding for the soul purpose of milage on these is a complete waste of time.

At a tank of feul per week, Pooks mods would take two years to pay out on gas savings, and thats using junk yard parts, and a shitty filter that should never be added to any engine that sees off road use. All this goes without mentioning that the 3% gains over a well maintained 4 litre xj are more then likely mythical anyways.

Keep it well maintained, keep the weight down, keep it geared properly, and watch your driving habits.

The rest is snake oil.

[Bnine]

I disagree with this general statement....so if you will follow me on my fairy-tail scenario..

Fact:  When I work near/at Fort Mac, I get noticeably better fuel economy then around Calgary.  Fort Mac is also quite hilly, perhaps not as hilly as Calgary, but it is definitely not a flat landscape.  Calgary Airport is 3553 ft above sea level.  Fort McMurray is 1214 ft above sea level. 

Theory:  I have read that for every 1000 ft increase in elevation you loose ~10% of your power.  A 200 hp engine will lose 20hp at 1000ft, and additional 18 hp at 2000ft, another 16hp at 3000ft, and another 7 hp at 3500 ft.  In Calgary, a 200 hp engine makes ~139hp, but that same engine in fort mac makes ~180hp

Jeeps are severely underpowered, no one will argue that, however if you add forced induction (enter fairy-tale land) you first somewhat negate the 10% loss per 1000 ft as you are now pressurizing the engine, plus you add over and above.  A normally aspirated engine is much more efficient at sea level vs higher elevations.

The stock 4.0l powerplant is starved of air in the Calgary area.  If you supercharged/turbocharged your engine, you would see gains in mileage, provided you maintained your driving style, i.e, a hill you drive up at WOT and can only maintain 45mph, that same vehicle with double the power will pull that same hill at 45mpg burning much less fuel as it is working at a much lower rate of work..

Perhaps thats not a good way of explaining it.  It was explained to me once like this, if you have a box that weighs 25kg, you as an 18 year old could carry that load much more comfortably and likely haul that load further than yourself as a 13 year old (unless you're benjamin button) because you are a much more powerful person.

Theory End.

The problem with my argument is there are not a lot of blown jeeps in Calgary (that I know of anyways) to compare.

You are confusing a boosted jeep with a properly geared one.

A 4 litre that is geared properly and isnt constantly shifted an lug will perform more efficiently resulting in better milage.

A boosted jeep just has the potential to use more fuel, and it will.

You can make minor improvements to 4 litre efficiency but its all starts internally. Until you get into cam profiles, and some head work, the rest is just bullshit.

Once you have the breathing efficiency increased, some add ons like a larger TB and headers will continue to help but still, with all that said and done, you are into 3000$ for 2-4mpg...........................................

Like I said, mod becaues you want to. Dont do it for milage.

Goes back to hub swapping for milage. 2000$ hub kit for half a mile per gallon. There's a 10 plus year payout

[Bnine]

you are kind of right al, but the 4.oL does not have a mass airflow sensor, they were calibrated at the factory to flow a certain amount of air, but air pressure does affect this. the factory just set these engines up to run under most circumstances, there are a lot of things that can be done to change their running characteristics but unfortunately if you are pre 96 (obd1 systems) they are hard to change. for instance i am running a 2001 intake on my 95 to improve airflow, but this is not really being used to its full potential because the engine management system does not know that it is now able to ingest more air. it did give me some improvements but untill i update my system to an obd2 and play with timing and injector pulse i will not use that intake to its fullest potential. therefore my gas milage sucks!

adding things like electric fans does change the gas milage but they are very marginal as the aerodynamics of any jeep is like said before a brick. little things like tire pressure or low rolling resistance plays a part too but just dont expect to gain much with little changes.

imho go ahead and change things and see what works for you, every jeep is different, what works on one might not work on another. but hey give it a try and share your results with others!

Pook

This is not true either Pook. Both OBD1 and 2 adjust fule mapping via data inputs from the 02 sensors.

OBD1 is actually easier to modify via the use of an adjustable map sensor.

I've run piggy back tuners on my engines before. You can mess with all the mapping and timing you want on these things. At the end, its hardly worth the effort.

The only time I'd bother with tuning one of these is if you have detonation issue and dont want to run premium.

[scott slade]

   Wow... I sure know how to start a conversation...!!!!!!      I might try a new air intake and like some of you said.. keep it tuned up etc etc.  I never did do the math on the MPG, but I got around 350 to 375 kilometers per tank.  I did notice that the altitude seemed to make a difference.   Thanks for all the advice.  I plan to keep this rig fairly stock in regards to the drive line and never any bigger than 31's.  Yes, she is a brick in the wind,  but that's my Brick...   one side note...!!  upgraded stereo was a waste of money when running a Safari top at 110 kph...!!!    %$#@  that was loud... but so much fun....!!!   Took the top off through the Mojave.... much quieter...!!