Jeep 4.0L question

[jeepster]

Hey guys

I got a jeep 4.0l question for the jeep guys here.

First of all, I find the Internet very confusing these days, way too many other forums where immediately after somebody asks a question it just turns into a flame war, and can never find any real good info. I'd rather ask a question here on Hunt Wa and get an "I don't know" or a "not sure" than any other site.


Anyway my question.... I got a 2001 TJ with the 4.0 with 105000 miles and my mileage is in the pooper, I'm getting like 12.5 mpg, about 180-190 miles per 14 gallon tank running mid grade. It should be getting 15-18 mpg, but not. I obviously need new tires, and I've opened up the intake and exhaust, and I'm going to do the oil change (Mobil full synthetic + zinc additive) Tuesday but even with fresh oil, it might get to 13mpg, for a few weeks then drop back down. It's been idling periodically like crap too, takes a while to start, acceleration is ok, but, everything is kind of pointing to fuel injectors. My first thought was the valves, but to my surprise I found out it has hydraulic lifters and adjusters, which in some ways is convenient (being a mechanic, kind of disappointing for weekend jeep tinkering), but after some readin, it's really sounding like its fuel injectors.

My thoughts, and the way I work, is if something is going to get removed, upgrade it to something better than it was, so, i am considering doing the "Ford 4 hole" or Bosch injectors. The logic is that the injectors will give a better spray pattern, better atomization, thus better burn rate, and compared to tired old stock injectors, it should be a small performance increase ( getting my engine acting like-new). I realize the limitation of the jeeps ECM, o2 sensors, and understand that simply putting larger injectors into my engine won't change anything, because of the parameters in which the engine is designed to run, and that the brain and fuel pump will still only shoot a certain amount of fuel into each cylinder regardless of orifice size on the injector, but again, it's about the atomization and spray pattern, unlike a carbureted engine where you can swap out jets and monkey with timing and get more power when coupled with other minor mods. the numbers I'm getting for injectors are for the non "High-output" 4.0 are either 19lbs ford or 22lbs ford injectors, and for the "High-output", you can go up to 24lbs.

So what I am wondering is if anybody has done this (mod works on any 4.0l), or has even heard of this, and hopefully could give some insight.

Stock wheels, 30" tires, glass pack exhaust, super chips flashpaq tuner currently reset to stock, mileage hasn't changed on performance [rich fuel air mix] or econo [leaned out]  and a custom cold air intake (more like hole saw and sawzall job to the stock box, and replacing all the correggated intake pipe sections with hose)

I am also thinking about increasing the plenum between the manifold and throttle body by adding a spacer.....

Anybody have any other mileage increase ideas aside from doing an engine swap for a turbo diesel 4 banger?

[jackelope]

I worked for Jeep for 10 years and I'm 90% sure I've never seen a wrangler get 18mpg. What makes you think the injectors are bad? Onboard diagnostics would be setting rich or lean fuel fault codes if they were that bad.  I'm not sure I've ever seen a bad injector on a 4.0 but it's been a while so don't hold me to that. I personally think maybe there's a sensor acting up causing your rough idle. Auto trans or manual? I wouldn't even think about spending a bunch of money on injectors unless you want a performance boost. I don't think that's your problem. I think your wore out tires and winter fuel is probably causing the biggest drop in mpg's although it's not much. Are you actually calculating the gas mileage on paper or are you doing what you mentioned above with the 180 miles to the tank etc. That's not too accurate.

[deerhunter_98520]

I had a 2000 tj...it had 35s, arb air locker, lower gears, winch, 6" lift, along with about every bolt on option you could get....power chip, full exhaust from header back, k&n intake, throttle body spacer and all it did was suck the gas...I was lucky to get 12 mpg...part of the reason I got rid of it and got a Tacoma....it ran great and had alot of power but it sure liked gas....had it a few years and never got more than 12 even on the highway

[papisjeep]

most 4.0 wranglers in my xp lucky to get 15 mpg
even worse if it had auto trans

[jrebel]

I'm running a completely stock 2000 tj with 4 liter and if I get 15-16 I am doing 50 mph with a stiff tail wind.       I haven't really payed attention, but I bet I am getting 12-14 with city driving.  12.5 seems about right.  There is a guy looking to buy a TJ on the forum if you are not happy with the mileage....he may take it off your hands. 

[Alchase]

My XJs and MJ with 4.0 never got more then 15 mpg ever. My MJ with a 2.5 never got better then 21 mpg.
I would break it down to basics. Plugs, wires, fuel, proper tire inflation, either can make a couple mpg difference.
A word of advice, unless you have ran synthetic oil the whole time, I would not recommend starting synthetic with over 100 k miles on a 4.0. Everyone I knew the tried synthetic on high mileage 4.0s ended up with rear main leaks.
The 4.0 is a strong, long life motor if kept with clean oil and basic maintenance, it has never  been called a gas miser, and honestly no tuner or after market gimic has ever made the 4.0 anymore efficient. Believe me thousands a thousands of jeepers has thrown the kitchen sink at it.

[jackelope]

Rear mains leak on 4.0L's running synthetics or not. I've probably literally made mortgage payments off the commissions I've made selling 4.0 rear main seals.

[huntandjeep]

I have never seen over 15 MPG out of 4 4.0 motors. The only thing Cold Air intakes , chips , throttle body spacers do for a 4.0 is lighten your wallet. The 4 hole injectors do atomize the fuel better but there's no mpg gain from them.

[deerhunter_98520]

Hey the cold air, chips and throttle body spacers give a little more power and make a cool sound 

[Special T]

I have a 4.0l in my xj im gona do it to. Same injectors are used in about 4 different rigs request dodge neon injectors for the lowest price and get them via rockauto.com for cheep. pretty discussions on this forum. http://www.jeepforum.com/forum/
I saw a pretty ridiculous price on reman4 hole for about $12 ea plus shipping. Ill probably go new. my injectors have 200K plus on them

[Wazukie]

My Son's 2000 XJ gets about 18mpg and also have a friend with a 2001 that gets that if not better. 

[Cougartail]

If I were to spend any money on this problem I would replace the catalytic converter & O2 sensors. Did wonders to my YJ which was suffering from poor mileage.

[Alchase]

Rear mains leak on 4.0L's running synthetics or not. I've probably literally made mortgage payments off the commissions I've made selling 4.0 rear main seals.

This is a true statement!

But, mine did not leak until 185k on one and 206k on the other using dino oil. And almost all of our XJ group who switched at high miles, leaked within a short time. Way too many for it to be coincidence.

[jackelope]

Rear mains leak on 4.0L's running synthetics or not. I've probably literally made mortgage payments off the commissions I've made selling 4.0 rear main seals.

This is a true statement!

But, mine did not leak until 185k on one and 206k on the other using dino oil. And almost all of our XJ group who switched at high miles, leaked within a short time. Way too many for it to be coincidence.

What' a MJ?

[Alchase]

 

Oh My they get no respect! LOL
The MJ is the Comanche pickup, an XJ with a bed, LOL