Gas mileage

[Djmack]

every one seems to be claiming about 15-22mpg on their 4.0
i do seem to push mine a little harder because i deliver pizzas and am all over the place, but before i did that i just about only did long range driving on a previous job.

anyway. im only pushing about 9-13mpg max! any suggestions? ive got new plugs and plug wires, new oil, keep it in maintenance all the time..

maybe its a compression issue? i kinda assume that maybe the previous owner didnt take the best of care of the poor thing... but should it still be running so low?

Note: i have an AX15 tranny which allows me to push more before shifting... this could be another problem.

[Alex22]

How many miles, what year?

Check the air filter, if its really dirty it will have an effect, how old are your O2 sensors. As the sensors get old and start to malfunction they will read lean so the comp adds fuel when it isn't necessary.

Mine only gets 15ish with the 4.0 and an AX15 which is why I bought a VW TDI 5speed.

[Djmack]

227,xxx miles, and a custom KNN air filter which is cleaned every 2,500-5,000 miles depending how much dirt i go through.

the o2 sensor is fairly new, but could have gotten burned up when the wires got smashed, and the sensor couldnt recieve or send any info. which could have caused the engine to have run rich.

but other than that, maybe dirty valves/injectors?

OH! another thing... when i build my stroker, do i have to put in better quality gas? im reading the stroker guides and its mentioned premium fuel like once or twice.

[ajmorell]

I know this isn't what you want to hear but you have to realize you are driving a Jeep, not a Honda. If you want a vehicle for mileage buy a 4-banger. There are potential gains to be had and it sounds like your Jeep in particular is getting crappy mileage but my ZJ was only getting 12-14 city and I would imagine that is the majority of what your driving is.

[Djmack]

yea your right... i do deliver pizza's and when i decide to start working on my engine im gonna need something to drive.. so i was thinking about dropping a small $6k loan on a jetta tdi, they get like 35-50 mpg
plus its diesel, Plus! its got a turbo meaning i can put on a small blow off valve lol.

[lafrad]

LoL... I think you need a throttle blade for a BOV to work... Diesels have no way to make a BOV work unless you get the boost up and activate it yourself with a switch.

[seanyb505]

9-13 seems low, the lowest I would ever get with th 4.0 was around 16-17 in the city. You can design the build to run on low grade or high grade. Its up to you.

[ajmorell]

9-13 seems low, the lowest I would ever get with th 4.0 was around 16-17 in the city. You can design the build to run on low grade or high grade. Its up to you.

It depends on the terrain too. At school where everything is straight up or down hill I can't get better than 12. At home where it's flat I can get 15-16 around the city.

[Djmack]

so any idea on how i could improve my gas mileage? i increased airflow with a better brand new air filter, i do routine oil changes, just changed my transmission gear oil, could the fuel filter effect it alot?

[Muad'Dib]

I would say your reported MPG's are about right for the type of driving you do.

[the_wrench116]

i get 14.96 as of the last tank and i have a bunch of work done but try swapping a qt. of motor oil for a qt of tyranny fluid right before your next oil change. let it warm up and then change it the extra cleaning additives will help get grit out of the crank case and the ring pack if your rings are all gummed up that could lead to crappy milage. one way to tell if you have blow by is to pull the intake off the throttle body and look in there if its oily looking well there you go.

[Heck]

I boosted my mileage from 13 to 16.2 when I finally (after a couple years) figured out that my catalytic converter was plugged. With over 200,000 miles, if you still have one, you should check it.

[the_wrench116]

oh my compression was 153 155 155 155 156 154. and thats on a renix long block with a high output intake manifold.

[supaflyak314]

I went from 9 around town to 12-13 around town after I found out my flowmaster cooked my emergency brake cable to the drum. "brake drag" according to the chrysler manual. My passenger drum was engaged, not enough to tear it up or excessive heating but enough to cause some drag to kill the mileage down pretty bad. (I even though it was a tranny problem, $6,000+) So it's another thing you could check... no one on the boards ever brought that idea up so hopefully others may find this help to them.

[Flash]

89xj, with 300,000+ on the clock, manual tranny, 14.xx consistently at at 6800' feet above sea level