Splatmaster527

Hey guys Im new to the forum so cut me some slack if im off in anything.

Here is my question. My dad wants to get a 2001 XJ and swap the Inline 6 for a 4 yes not a 4 to a 6 but a 6 to a 4! What he is looking for is maximum fuel efficiency 25+mpg. Im wondering if this is even possible and if it is would it be worth the work of installing and upgrading the 4 or would we be better off trying to gain as much efficency out of the 6 as possible i.e. new internals, turbo, cold air intake, ect...
What I am worried about the big problem being is the whole computer system because as far as i understand the CPU is very intertwined with the whole vehicle in the newer XJs

Thanks in advance for any help.

Stan6406

My 4.0 auto gets better mileage then my 4cyl 5Spd. Got to have it to the floor alot when I have to go up hills

jeepxjho

Swapping in a 4 cyclinder for the 6 cyclinder would cost more then making the 4.0 more fuel efficent since like said with the 4cyclinder you are having to have your foot to the floor to get the jeep to do much.

Now for refrence a 2001 jeep cherokee with 4.0 with auto trans shows 16 mpg city/ 21 mpg highway the 4 cyclinder with auto shows 19 mpg city and 22 mpg highway from consumer report.com.

So swapping in a 4 would be a complete waste of time and money and of a good 4.0.

I would suggest getting a cold air intake, low restriction exhuast and a more free flowing header to get the most out of the 4.0 along with doing normal maintence like new plugs and wires and maybe a new o2 sensor depending on the miles.

So swapping in a 4 for a extra 2 mpg isnt worth it.

But remember the jeep does have aero dynamics of a brick LOL not really but you get the idea.



Now one thing he can do if he really is trying to get the most out of the 4.0 is swapping in a manual tranny if it has auto that will net him a few more mpg if he wants the most out of it.

Stan6406

Actually if your looking at a Jeep for gas mileage for the most part they are gas pigs for the weight and engine size. I choose to blame it on the gearing and my wife doesnt give me enough allowance.

Splatmaster527

ok thanks a lot guys for all your help

if we end up going with the jeep it sounds like the 6 is staying in and getting the crap modded out of it

how hard would it be to make an auto a manual??? seems like there would be a lot of trouble getting pedals, shifter and other manual trans components to fit.

ktmracer419

even if a 4 cyl would get 6 mpg better it would take a long time for you to recoup the costs involved with the swap.

lets say the average person drives 12k miles a year

you find a nice maybe rolled or crashed running 96+ (obd2) 4 cyl donor truck to swap the entire electrical system, engine, and drivetrain from (good luck finding that, there about like 6 made lol)

pick it up for a cool grand.
need another grand of parts to get it all to work in your jeep (yes that being realistic)

so $2000 is what it would cost you to do the swap (plus the headaches and time involved)


at 12k miles and 18 mpg you would go through 667 gallons of gas a year

at 12k miles and 24 mpg you would go through 500 gallons per year

at $2.50 a gallon that's $417 per year

it will take you nearly 5 years to recoup the costs you put in the swap.

might be worth it to some people. but not me.

funkle95xj

Honestly if you are going to swap something in with fuel efficiency in mind, and were even condsidering a 4.0-2.5 swap and all the headaches involved, look into a 4BT Cummins diesel swap. It's the 4 cylinder version of the beloved 6BT 5.9L diesel found in full size Dodge trucks. I have seen this swap do extremely well mileage-wise even in lifted Jeeps with larger than stock tires. I can only imagine the kind of mileage you would get if this was a build specifically for fuel economy (Stock tires, stockish gear ratio, stock ride height, etc...) check out this site for more info!

http://www.4btswaps.com/forum/index.php

McRay

I am thinking you get gas mileage with rear in gear ratio has anyone swap out rearend for highter geared rear end to for better gas mileage

Stan6406

Have to change gear ratio in both axles. You can't change just one.