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

[jeepster]

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?

A Jeep MJ is mommy's Jeep

Kidding aside, its the Comanche, the Cherokee based pickup


Yeah my tj leaks and has leaked for a while, I've ran synthetic whenever I could afford it for the last 5 years, and regularly for the last 2. Bought this thing used in 07 with 14,000 miles and plan on having it alot longer.

Guess I've been working on diesels too much... If they run like crap, change the oil, do the valves, drop in new injectors, give it new filters and call it done

So if you say put on a new cat and 02 sensors, couldn't I bash the kitty and install dummies? It's not like I'd ever have to get it emmision checked, I live on North Whidbey and plan on going to Alaska, so, I'd never smog it.... Not exactly legal but.... It don't bother me. Probably would be  cheaper... And would never have to worry about it again.....thoughts?

[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.

What' a MJ?

A Jeep MJ is mommy's Jeep

Kidding aside, its the Comanche, the Cherokee based pickup

the Wish-I-was-a scramber pickup

[jackelope]

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

Gotcha. We never saw too many of them at the dealership. I can remember 1 guy who spent a God awful amount of money on one, but that's the only one I can reliably remember.

[HUNTINCOUPLE]

Our 97' TJ had a rough idle so I pulled all the injectors and took them into DR. Injector. He pulled them all apart and ckenned them. He said they didn't look bad at all. This was at about 50,000. He said the stock injectors are very well built. I did do the O2,sensor and others. Still idels more rough than I like but always starts and runs. As for fuel miledge 12 on a good day.

[Thehowler]

Dealers just love to report back that you need a injector cleaning anytime your in for a running issue. jeep or Ford dealers didn't matter.
Before I did all my own wrenching, I had a jeep wrangler in for a running issue at 99,000 miles. One thing they called back that needed to be done urgently, was my very dirty fuel injectors needed cleaning, and also a new Map sensor. I had them only do the map sensor and it ran light a top. I never once cleaned those fuel injectors and ran that motor for 275,000 miles before rebuild. Always Chevron gas.

[jackelope]

I repeat, injectors in a 4.0 hardly ever go bad. I can say the same thing for Ford injectors since you brought it up. We don't replace too many gas engine injectors in Ford vehicles. It's never a bad thing to maintain your vehicle and clean your injectors once in a while, but it's not too often that they go bad. Back in the day, we used to fix lots of GM misfires doing a Motorvac injector cleaning. Ive seen that the effectiveness of an on-car injector cleaning varies greatly from machine to machine. A Motorvac machine works well and some of the other machines suck. If someone is telling you your injectors are very dirty, ask them how they know that. That should give you an idea of whether they know what they're talking about or not. Chevron fuel is great and has techron in it, an injector cleaner, that will work over time. I can't speak for all dealers but I've seen just as much "snake oil" sold at independent shops or jiffy lubes as I have the dealers. Try going to jiffy lube for an oil change some time. The BS meter will be pegged on high.

[rudysts]

I had a 2001 Cherokee that had an idle issue it had nothing to do with the injectors. it was much worse it turned out to be a cracked head this is actually a common problem for 99-01 years. I hope you don't have that problem good luck to you. you can easily google this problem.

[Thehowler]

Jackelop,

Have you heard of a injector- fuel system cleaner called BG44K, PN 208? I've talked with a few folks recently that swear by dumping a can of this in a full tank of gas.

[jackelope]

No I haven't but that's not saying much. I believe that those type cleaners are best used every so often as a preventative maintenance type thing. I've always heard that Techron is/was the best.

[Wacenturion]

I've got a 2003 Sahara Wrangler as a tow behind for my motorhome.  All stock with the 4.0, manual tranny and I get 16.5 plus or minus.  Has 65k original miles.

[dewandgin]

Jackelop,

Have you heard of a injector- fuel system cleaner called BG44K, PN 208? I've talked with a few folks recently that swear by dumping a can of this in a full tank of gas.

Used BG44K all the time when we used BG. I have friends that use it to smog vehicles in California. Vehicle will not pass running to dirty. Put a can of 44k in the tank fill it up and go drive it for 30 miles and smog it. It will pass almost everytime.

We have 2 CDJR dealerships and I have rarely/never seen a 4.0L with a automatic 4X4 get more than 15mpg on a really really good day. Check for exhaust leaks at the exhaust manifold cracking and make sure you use champion plugs (in my experience the run better and smoother) and as others have said tires aired up, tuned up and smooth starts and stop.

My 4.0L Cherokee has never got more than 14mpg.

[Alchase]

Forgot about the rear exhaust manifold bolts. The are notorious for breaking.

I had a 2001 Cherokee that had an idle issue it had nothing to do with the injectors. it was much worse it turned out to be a cracked head this is actually a common problem for 99-01 years. I hope you don't have that problem good luck to you. you can easily google this problem.

A cracked head on a low miles 4.0?
That one is new to me. Even the ones that had the cooling system issues and overheated rarely ended with a cracked head.
 The MAP or MAT sensors, EGR, TPS can cause a loss of power or MPG as well.

[jackelope]

I've seen the cracked heads  thing.
The exhaust manifolds break all the time. Down near the collector.

[Thehowler]

The cracking of the cylinder head on the late 99, all through 2000, and the first part of 2001 was a major problem for many jeep owners. Head casting #0331. If your looking for a used jeep to fix up in those years, look at the cylinder head on the driver side top. If you see those numbers, slowly back up and walk away.

[coachcw]

your fuel trims could be off do to a weak oxygen sensor slow to respond . opening up the exhaust could aversely effect your millage by causing a loss of bottom end torque. I'd make sure that your thermostat is a 192 and works , and possibly throw a fresh upstream oxygen sensor in it . as far as injectors spary pattern will effect idle more than cruise and probably isn't effecting millage in less its running rough.