Help I need more MPG's, will any of these help..

[Mr Clean]

Would any of theses modifications help in gaining 1, 2, 3 or more mpg's?
Throttle Body Spacers, headers, cold air intake or a performance chip or any others I may have overlooked. I already have the Dynomax exhaust set up installed.
My XJ is my dd; 55 miles round trip to work & home 4 days a week plus around town only when necessary. I'm going thru about 1.25 tanks per week costing me about $240.00 per month now but when gas hits near $5.00 per gallon I'll be well over $300 + per month for gas.
Besides keeping my tires properly inflated and the brick off the gas pedal what else will help in any way, shape or form in gaing a few more mpg's per tankfull?

P.S. I'm not a fan of drafting the semi's on I 95 so that's out.

[Brasscatz]

The thing I keep hearing about throttle body spacers, is that they don't do diddly. I don't have one so I cannot vouch for that. Headers and cold air intakes advertise a small gain in mpgs and hp, and from past experience on other cars non-Jeep, this has been somewhat true. You mentioned tires properly inflated and the brick off the gas pedal, yes that helps. So do good plugs, wires, cap, rotor, etc. Clean air filter (whether stock or aftermarket). Overuse of your brakes can actually hinder gas mileage. Start slowing down sooner and softer when possible. Another myth is that it takes more gas to start your car than it does to idle... it actually uses more to idle, so if you shut down at stoplights, that will help. You can improve your gas mileage by 1–2 percent by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1–2 percent. Be wary of any gas-saving claims for automotive devices or oil and gas additives. Even for the few gas-saving products that have been found to work, the savings have been small. Also, windows down instead of using the a/c. Cruise control also helps. Pick a speed and set it. Prevents your foot constantly changing throttle pressure. I actually use my cc every where, highways and regular streets.

[Brasscatz]

Here ya go. Found this site.
http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/

Hope that helps!

[Mudderoy]

I've been monitoring my mpg since the summer of 2008(?) and nothing has changed my gas mileage (of any notice) with the exception of the 4.56 gears. There was about a 2 to 3 mpg increase. I was running 3.55 gears on 32" tires originally. Now I am on 33" tires with 4.56 gears, custom front bumper, winch, 4 KC lights on said bumper, custom rear bumper with tire carrier and spare tire, slyders with frame stiffeners... mpg has remained near dead constant.

Matt and I are working on a new 4.0 to go into it in the next couple of months. After that I may try one of the chip programmers that talk about programming for better mpg.

I'm hopeful that my mpg issues have been a poorly performing engine, but I suspect I'll continue to see 12 and 13 mpg.

[4.3LXJ]

Change your O2 sensor regularly. It is what determines the fuel air ratio. A front air dam helps. Mine had one from the factory. Throttle body spacers were designed for throttle body fuel injection. They are worthless on direct injection.

[bluedragon436]

Yeah I could always use some extra MPG's.. I would love to upgrade my gears, I know that will help some.. but I am always looking forward to finding better gas mileage.. I have thought about trading my XJ in, just because of the mileage I have to drive every day to and from work, but would rather just get the best I can out of what I have, and continue to enjoy my XJ as I have thus far!!

[Mudderoy]

Change your O2 sensor regularly. It is what determines the fuel air ratio. A front air dam helps. Mine had one from the factory. Throttle body spacers were designed for throttle body fuel injection. They are worthless on direct injection.

I understand what you are saying here and agree from a logical standpoint, but I tried this before swapping in the gears. After 120k miles (at the time) the new O2 sensors didn't make a notable difference. One thing I do remember reading about was a bad power steering unit costing about 2 mpg.

I may be changing mine out during the motor swap.

[Mudderoy]

Here is a really good thread talking about real world things tried and failed.


I bought one (Hypertech Max Energy E-con programmer) a long time ago, when they first came out in Quadratec and 4wd catalogs. Don't waste your money. I paid around $400 for mine and may as well bought a brick. No mpg change (13 before and after ). It also advertised that it would correct speedometer for oversized tires, but doesn't for my 01 TJ. I have never read a good review on these anywhere, but I didn't look for them until after I fell for it. I also don't believe they ever update the software like they advertise, but the way it's set up you can never tell. I listened to all the hype when I first bought the Jeep from a place that sells lots of lifted trucks and Jeeps and they said how big a difference a CAI, TBS, exhaust, and programmer make in everything. I was single at the time and had the money to waste, and did just that. Installed all that crap at about the same time. Added exhaust a couple days after. If there is any difference I would say it just sounds meaner on acceleration. If I could do it over again I'd have put the money towards a regear and lockers. Like the exhaust sound, but doubt it added any power, definately nothing noticeable but sound.

:link: (http://www.wranglerforum.com/f5/hypertech-max-energy-e-con-reviews-106317.html)

It mirrors what I have experienced, at least in as much as the only thing that made a big positive difference in my mpg was re-gearing.

[Cheromaniac]

Would any of theses modifications help in gaining 1, 2, 3 or more mpg's?
Throttle Body Spacers, headers, cold air intake or a performance chip or any others I may have overlooked. I already have the Dynomax exhaust set up installed.
My XJ is my dd; 55 miles round trip to work & home 4 days a week plus around town only when necessary. I'm going thru about 1.25 tanks per week costing me about $240.00 per month now but when gas hits near $5.00 per gallon I'll be well over $300 + per month for gas.
Besides keeping my tires properly inflated and the brick off the gas pedal what else will help in any way, shape or form in gaing a few more mpg's per tankfull?

P.S. I'm not a fan of drafting the semi's on I 95 so that's out.

Additional weight plus a lift, bigger tires, and brick-like aerodynamics will always work against you. Going back to stock height suspension and stock size tires will help a lot if you're prepared to reverse the mods. Shedding weight from the Jeep (and from yourself) will also save fuel.
A performance chip is a big waste of money. A cold air intake, larger bore TB, header, and exhaust will add performance and may improve cruising fuel economy slightly, but much depends on your driving style. A curved runner '99+ intake manifold may also improve mpg by providing a more even air distribution to all cylinders and if you do that swap, don't bother with a TB spacer.
Even if you improve fuel economy by 1mpg, it'll take a long time to recoup the cost of the mods from fuel savings.
You might want to consider buying a smaller car to use as a daily driver and keep the Jeep as a weekend plaything.

[LizardRunner]

The easiest way I know to increase fuel mileage is to get a complete burn of the cylinder charge every time the plug fires. To do that you would start with the ignition; plugs, wires, distributor, coils, grounds. Next to attack would be the fuel air mix where you would want the fuel to be a very fine mist. Injectors would need to be multil hole, super fine mist type. air flow would need to keep the fuel in fine suspension for a total burn.

[Mudderoy]

I see lot of good advice here, but has anyone ever personally experienced documented evidence that any of these work?

I ask, not to start a fight, but while researching all of this a couple of years ago I have found none of it made any difference for me. I'm just wondering if this "general" information is propaganda that has been put out that we are all regurgitating, or perhaps it just works on another type of vehicle, or maybe even any OTHER vehicle besides mine.

Injectors, 6 hole replacing the OEM 1 hole, no change in mpg...
Performance Distributor Fire Wire kit, coil, plug wires and larger gap on champion plug, no change in mpg...

Have I removed stuff to make my Jeep lighter, no, did I add a bunch of stuff that made it heavier, you betcha! No change in mpg...

[XJ Wheeler]

I've only done one mpg figure and that was a few years ago. I was getting 15.5 but that doesn't include my speedometer not being recalibrated (actual should be slightly higher). Since then i have swapped out my brothers poorly worn bfg mt's (the original design) for near new and smooth bfg alls, installed the Firepower ignition kit w/ Bosch platinum plugs set at .065 gap, custom cat back w/ magnaflow muffler, and poweraid throttle body spacer (clean throttle body too). I plan on doing a couple runs to Houston soon so i plan on getting a figure then (if my speedometer will cooperate) and am hoping for maybe 18?

As far as getting better mpg's there is of course some of the engine mods that work for some and not for others and others that are usually a guaranty. I've always wanted to delete the mechanical fan for an electric unit for mileage, power, and less strain of the engine.

Shedding weight is usually an easy way of gaining. Your rolling weight plays a big part as well. A lighter, smoother, and less aggressive tire and wheel combo can be surprisingly effective.

Aerodynamics is key, roof rack and spares on the roof is an instant killer for mileage.

Gearing is probably one of the most effective, but also one of the most expensive.

Most of this is just from what ive heard and read so don't quote me on it.

[Carves]

Even if you improve fuel economy by 1mpg, it'll take a long time to recoup the cost of the mods from fuel savings.

:thumbsup:

Yep .... that 1mpg equates to what .... 20 miles per tank and a saving of maybe $ 4.00 a tank ?? .... pffftttt .... drink a coupla beers less a week ... and enjoy the XJ.

Not saying that its not worthwhile trying to optimise your fuel consumption ... but the amount of money and bling some people go through to get a negligible improvement ... is entertaining at times.

XJ fuel economy is as about as good as it gets ... as it came from the factory ... altho a set of better flow headers/exhaust and removing the roofrack/rails might have seen an improvement at highway speeds over the long term.

Rehashing other peoples comments and adding a few of my own ....

Some common maintenance items to maintain fuel economy ...
- quality fuel,
- tyre pressures,
- wheel alignment,
- plugs, leads, dizzy cap, coil, injectors, throttle body & parts, airfilter ... keep em clean/adjusted ... fit better gear when they are due for replacement.
- Injectors
- O2 sensor ... Whilst it doesnt do much for improved fuel economy ... a dodgy one will certainly increase petrol consumption considerably.
- Engine and Diff Oil ... Thin oil for economy .... slightly thicker for better wear protection / hotter weather, cold start temps.
- Engine Coolant Temperature ... Properly working, tested, temp sensor to ensure the PCM is selecting the "best" fuel tables, and a constant, 190*/200* temp ... The PCM accepts 160*/170* as "warmed" but its probably running on a slightly richer, fuel table compared to 190*.
- correct fanbelt tension.

Some common XJ stuff that increases fuel use ...
- Removing the front air dam - to gain clearance,
- Suspension lifts ... raising the vehicle increasing wind resistance/drag,
- A/T & Mud tyres,
- Wider and higher profile tyres,
- Roofracks/baskets and light bars,
- Racing ricers,
- great heavy lumps of metal bolted on front and rear, full of winches, lights, spare wheels and jerrycans,
- rear cargo area full of winch gear, hi-lifts and stuff for those inevitable "trail repairs" ... like Fridges and Eskys full of beer & ice :D
- Expecting regearing to overcome the rolling resistance/weight of bigger tyres ... Regearing just lets the engine spin the bits easier ... fuel savings occur but regearing wont get back the factory, shpping trolley, family wagon, daily driver, fuel specs.

All the above are mostly "nescessities" for a lot of us using an XJ as a daily driver and a play vehicle ... so we pay the price for it ...

Its a bit like, thinking about cheating on your missus ... If you're not prepared to accept the consequences ... Dont do it ;)


Electric fan conversions .. to gain HP and Fuel economy. :rolleyes:

When I see a written report of multiple XJs, before and after tested - on a dyno and the highway ... showing worthwhile, short & long term improvements ... I might consider hacking the engine bay to bits to fit something.

"reported" 15% gains are in relation to what ??? ... fitting an electric in a 1970's solid fan vehicle, or a fixed speed, non-thermal fanclutch vehicle ... or in an XJ, with a variable resistance, thermal fanclutch ?? ... ;)


E-Bay magic stuff ..... is just e-bay faerie tale stuff me thinks ... Duct taping a raw egg to the go pedal - would probably be a lot cheaper .... and more effective .. :D


Piggyback computers/chips ... :rolleyes:

20yrs of sales of the 4.0l XJ ... I'm pretty sure the PCMs fuel tables, already have the old girl running as lean as possible ... so the manufacturer could keep the govt and the greenies happy.


For those who think Closed Loop is an important consideration ... Yep it is - Primarily to optimise the mix for the cat converter operation.

The OBD 4.0l XJ is in Closed Loop within a coupla minutes after a cold start. Its also - Only in Closed Loop in various modes ...

- Ignition switch ON
- Engine start-up (crank)
- Engine warm-up
- Idle ................................................ Closed Loop
- Cruise ............................................. Closed Loop
- Acceleration
- Deceleration
- Wide open throttle (WOT)
- Ignition switch OFF


So all you leadfoot drivers ... and poor sods dealing with stop/start traffic probably dont see Closed Loop much anyways ... :D

I've found it generally stays in Closed Loop under controlled acceleration tho ... So dare I say "driving style" is an important consideration ?? ... :D


Something that was useful to a degree - was a vacuum gauge ... Some vehicles even had them fitted as "economy" gauges .... but I think peoples were concentrating more on the gauge - than on the road ... :bang:

[Cheromaniac]

Electric fan conversions .. to gain HP and Fuel economy. :rolleyes:

One some vehicles this does actually work but any improvement in mpg is likely to be in city driving where you drive at slow speed or idle. It's under those conditions that a mechanical clutch fan will impose more drag on the engine and absorb HP 'cause it spends more time locked up. You won't see any mpg change cruising on the highway.

[LizardRunner]

It's far easier to increase hp than mpg and more fun too. Tony, if you took all your heavy additions off, you probably would have seen about a 2mpg increase. I don't really try to increase mileage but I do know how, it just takes a 231 turbo, money and fabrication. the end result is smokey's fuel homoginizer, best used with a re-profiled cam, forged pistons and carrillo or similar rods. 45-50 mpg and much more hp. Of course on our 4.0L engines you also have to change to a throttle body injection set up.

[Mudderoy]

It's far easier to increase hp than mpg and more fun too. Tony, if you took all your heavy additions off, you probably would have seen about a 2mpg increase. I don't really try to increase mileage but I do know how, it just takes a 231 turbo, money and fabrication. the end result is smokey's fuel homoginizer, best used with a re-profiled cam, forged pistons and carrillo or similar rods. 45-50 mpg and much more hp. Of course on our 4.0L engines you also have to change to a throttle body injection set up.

Well since the mpg didn't go down as I added them I find it hard to understand how it would go up if I removed them, but I ain't taking them off. :D

[LizardRunner]

the added weight means your engine is doing more work to get the same speed as before you added the weight. more work = less mpg, less work = more mpg. it's just physics. Now since you didn't see a drop in mpg that means you must have increased the mpg with your changes to the air pump (engine) if you hadn't, you would be getting less mileage now.

[Mudderoy]

the added weight means your engine is doing more work to get the same speed as before you added the weight. more work = less mpg, less work = more mpg. it's just physics. Now since you didn't see a drop in mpg that means you must have increased the mpg with your changes to the air pump (engine) if you hadn't, you would be getting less mileage now.

Hey, I understand the logic of it, but the data doesn't reflect it. I have considered the explanation that you put forth, changes to the performance off set the changes in weight. I haven't correlated the dates of the changes with the dates of the mpg data, but my "feeling" (which is where people usually get in trouble) is that they were to far between the changes and it would have shown up in the mpg data.

Now to be completely honest, there is a slight downward trend in the mpg over a year, but we are taking a fraction of a mpg. This could be due to the changes, I'm thinking with the recent issues I'm having with the engine, it's just the engine wear.

[Mr Clean]

Additional weight plus a lift, bigger tires, and brick-like aerodynamics will always work against you. Going back to stock height suspension and stock size tires will help a lot if you're prepared to reverse the mods. Shedding weight from the Jeep (and from yourself) will also save fuel.
A performance chip is a big waste of money. A cold air intake, larger bore TB, header, and exhaust will add performance and may improve cruising fuel economy slightly, but much depends on your driving style. A curved runner '99+ intake manifold may also improve mpg by providing a more even air distribution to all cylinders and if you do that swap, don't bother with a TB spacer.
Even if you improve fuel economy by 1mpg, it'll take a long time to recoup the cost of the mods from fuel savings.
You might want to consider buying a smaller car to use as a daily driver and keep the Jeep as a weekend plaything.

Well my XJ is mostly stock, I did change the injectors from 1 hole to 4 hole and added the Dynomax exhaust, but other than that with 29" tires and no lift to speak of it's normal. Shedding weight; there's no additional weight my XJ (or I) carry :D. I could remove my spare but if I do I will without a doubt I'll get a flat, in a cold rain, at midnight on I 95 on my way home from work so I think I'll leave it where it's at.

[Mudderoy]

Well my XJ is mostly stock, I did change the injectors from 1 hole to 4 hole and added the Dynomax exhaust, but other than that with 29" tires and no lift to speak of it's normal. Shedding weight; there's no additional weight my XJ (or I) carry :D. I could remove my spare but if I do I will without a doubt I'll get a flat, in a cold rain, at midnight on I 95 on my way home from work so I think I'll leave it where it's at.

Maybe you mentioned it, but how it the air dam? Also I recommend keeping accurate mpg records so you can see what helps, what hurts, and when it may be time to change air filter, oil, transmission fluid, or even gas stations.

There are several good apps for Android phones that you can use to keep up with your mpg easily.

[Mr Clean]

Maybe you mentioned it, but how it the air dam? Also I recommend keeping accurate mpg records so you can see what helps, what hurts, and when it may be time to change air filter, oil, transmission fluid, or even gas stations.

There are several good apps for Android phones that you can use to keep up with your mpg easily.

The air dam is in place. Tires infalted to 33 on all four corners, a stock XJ except for injectors and exhaust.

[Cheromaniac]

I recommend keeping accurate mpg records so you can see what helps, what hurts

I've owned my Jeep for almost 17 years and I've been tracking gas mileage since day 1. I've found that you might gain 1-2mpg over stock with a few bolt-on performance mods to make the engine more efficient and by removing the roof rack bars to aid aerodynamics. If you have an older XJ with the log type intake manifold, swapping in a newer curved runner manifold might also give you a small mpg increase.
I've done all of those things and despite having a 4.6 stroker and almost 30% more HP/TQ than stock, gas mileage is slightly better especially on the highway.
Cruising at 75mph I get around 19 miles per US gallon (23mpg Imperial) or 12L/100km.

[AZDoug]

I saw a study with 3 late model Ford F150s. they were set up like a typical PU toolbox and 100lbs of stuff in it. They did all the common things, bed cover, air gate, leaving the tailgate down. The single thing that improved the MPG the most was taking the toolbox and 100lbs out. And a side note was dropping the tailgate screwed with the aerodynamics and lower the MPG

[Mudderoy]

I've owned my Jeep for almost 17 years and I've been tracking gas mileage since day 1. I've found that you might gain 1-2mpg over stock with a few bolt-on performance mods to make the engine more efficient and by removing the roof rack bars to aid aerodynamics. If you have an older XJ with the log type intake manifold, swapping in a newer curved runner manifold might also give you a small mpg increase.
I've done all of those things and despite having a 4.6 stroker and almost 30% more HP/TQ than stock, gas mileage is slightly better especially on the highway.
Cruising at 75mph I get around 19 miles per US gallon (23mpg Imperial) or 12L/100km.

17 years of gas mileage data is impressive. I wish I had some records on mine prior to the lift and tires. Gas was cheap, and I didn't care. lol

[4.3LXJ]

One thing I think that would improve milage is the 2000/01 manifold. It not only has the larger ports, which increases horsepower, but more importantly here has equal length runners which would even out the air flow and not make a disproportionate amount of work done by some cylinders.

[Mudderoy]

One thing I think that would improve milage is the 2000/01 manifold. It not only has the larger ports, which increases horsepower, but more importantly here has equal length runners which would even out the air flow and not make a disproportionate amount of work done by some cylinders.

This is good to hear, the engine that will be going into the 98 is a 1995 and it will have the curvy intake on it. Already have it, but I do need to get it up to Matt in Conroe soon. Still plan on doing the port and polish.

[Cheromaniac]

One thing I think that would improve milage is the 2000/01 manifold. It not only has the larger ports, which increases horsepower, but more importantly here has equal length runners which would even out the air flow and not make a disproportionate amount of work done by some cylinders.

I did that manifold swap on my stroker nearly 3 years ago and ran my Jeep on the dyno afterwards. Peak to peak gains were 1.9hp/4.5lbft and most of the extra torque was in the 2500-4000rpm midrange compared to the old manifold. I also gained ~1mpg.
I ported the injector bosses of the new manifold before installing it. The no.3 and no.4 injector bosses protrude more into the runners than the others and need the most work to even them out.

http://www.angelfire.com/my/fan/HP_TQ.jpg

[Mudderoy]

I did that manifold swap on my stroker nearly 3 years ago and ran my Jeep on the dyno afterwards. Peak to peak gains were 1.9hp/4.5lbft and most of the extra torque was in the 2500-4000rpm midrange compared to the old manifold. I also gained ~1mpg.
I ported the injector bosses of the new manifold before installing it. The no.3 and no.4 injector bosses protrude more into the runners than the others and need the most work to even them out.

http://www.angelfire.com/my/fan/HP_TQ.jpg

How was the butt dyno? I mean could you feel the difference?

[Cheromaniac]

How was the butt dyno? I mean could you feel the difference?

My butt dyno has become very finely tuned to driving my Jeep for so many years so I can feel very small differences in performance. :D
The manifold that I found was from a junkyard '01 XJ and it cost a mere $54. It produced a 4-5% improvement in fuel economy and took me about 12k miles of driving to recoup the cost of the manifold in fuel savings.

[Mudderoy]

My butt dyno has become very finely tuned to driving my Jeep for so many years so I can feel very small differences in performance. :D
The manifold that I found was from a junkyard '01 XJ and it cost a mere $54. It produced a 4-5% improvement in fuel economy and took me about 12k miles of driving to recoup the cost of the manifold in fuel savings.

I love that last sentence. Gas mileage has to be pretty damn bad for most mods. To me the mod needs to be for something more than mpg. I love my 4.56 gears, as they make the Jeep drive like it did before the lift and the tires. Even better they improved gas mileage.

[Cheromaniac]

Gas mileage has to be pretty damn bad for most mods.

Not really. Don't forget that our Jeeps have digital EFI so it isn't easy to extract more mpg out of them but if you can extract more HP/TQ out of the engine and still have the same mpg as stock or slightly better, then I'd say it's a job well done.
Otherwise the only ways to improve fuel mileage (apart from moderating your right foot) are to reduce the weight of the vehicle and improve the aerodynamics. Unfortunately neither is feasible if you want to play offroad. Therefore your remaining options are to either live with the Jeep's thirst as a daily driver, or use it only on weekends and buy a smaller car to use as a daily driver.

[bigjim350]

Free flowing exhaust will help you get some more mpg. Its not a popular mod, but if ya remove your cat, then get a programmer that removes the rear o2 you will gain even more mpg. Plus it sounds alot better :)

[gary63]

this may be a little late but i reseved a full Edge package chip throtlebody and cold air intake . Also the edge insite. i have been using the insite and checking
0 to60 1/4 mile load intake air temp. water temp. and more . My xj is stock and now I'm starting to change and add things.also been watching my mpg for 2yr.
1 thing i have found is the cherokee likes slower speed 45 to 55 for the best mpg after 55 it goes down. also anything that make more hp and tork. the less you have to push on the rightfoot. i will try to keep you all up on what i find out.