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Improving MPG

SEXJ96

NAXJA Forum User
Location
California
Hello,

Im wondering if there is anything I can do to try and improve my mpg. I currently do around 12 on average mixed between city and highway, and I do use the fuel volume at the pump and my odometer to determine my mpg. The best i've ever seen it do is around 13 on a 500 mile highway trip.

Oh and also whenever I fill up gas, the most ive gotten in the tank is around 16 gal but my tank is supposed to be 20 so im guessing my fuel gauge is not that accurate. I dont drive much with the light on cause no cooling for the pump then.

Specs:

96 XJ, manual trans, 4.5" lift, 33x12.50 tires, pro comp steel wheels, JCR prerunner front bumper, JCR T-case skid, gas tank skid (steel), Synergy tie rod and drag link, rough country trackbar, synergy upper and lower control arms, Reese rear hitch, custom made rock sliders, rear cargo drawers, and stock gearing on 8.25 and d30.

I also have my tools, recovery equipment, and fluids always stored in the back.

AC on or off doesnt seem to affect it much, and I have done a tune up recently ~1 year and 13k ago. Tune up consisted of rotor, caps, spark plugs, fuel filter, injectors, air filter, etc..

Suspecting O2/MAP sensor but the car runs and idles fine.

Any suggestions for increasing my mpg?

Thank you,
Laith
 
The gearing is what's killing you!
 
if you have not changed your speedo gear you cannot rely on your odometer to calculate your actual fuel mileage, a better way to estimate your true mileage would be to drive a predetermined gps route and use the mileage stated there.

regearing to keep your engine running at optimal rpm would be a good start, do you know what gearing you have now? also cleaning injectors, temp sensor, iac could help, catalytic converter could be another source of fuel mileage dropping as well.

from what i have read 14-18 is about the best we will see on lifted heavy xj's you arent far off if not actually at 14 now.
 
Also, do you have a steel gas tank or plastic? 96's are a mix year!
 
I think re-gearing is going to be my best bet since I'm running on the stock 3.07 ratio...

I should have swapped my speedo gear for the right one when I did my SYE but i was in a hurry to get it done before a trip and I didnt have the new one on me. I will order soon and swap it out.

I should probably my injectors and IAC. As for the temp sensor you mean the one in the thermo housing or the one in the head?

I am also unsure of the condition of my catalytic converter, might just replace it anyways.

This thing is my DD for now and its a gas guzzler. Sometimes im pretty certain im leaking from somewhere lol.

My gas tank is plastic but I got the OEM skid plate that came on some of the cherokees on it.
 
the speedo gear will be dependant on tire size and your gearing iirc, so you will probably want to do that last. as doing it before the gear swap will leave you in the same boat as far as your milage being innacurate, i am not sure which temp sensor in the 96 you will want to clean. i cleaned both in my 99. i am about to regear as well, and have been fighting mpg also.

another thing i forgot to ask is if your exhaust manifold is leaking at all, i am pretty sure that will effect mpg also.
 
Oh and also whenever I fill up gas, the most ive gotten in the tank is around 16 gal but my tank is supposed to be 20 so im guessing my fuel gauge is not that accurate. I dont drive much with the light on cause no cooling for the pump then.

With the plastic tank that's about right for the "low fuel" light to come on. I once ran mine down to 1/2 gallon!
 
use cruise control as much as possible

Using cruise control on rolling hills kill my gas mileage.

I'm becoming convinced that 90% of the complaints regarding MPG is due to a very poorly designed and poorly maintained electrical system.

This here is very interesting. :dunno:
 
I'm becoming convinced that 90% of the complaints regarding MPG is due to a very poorly designed and poorly maintained electrical system.

And in typical fashion you spout off some wild thing with nothing to back it up and nowhere to go with it. Maybe it needs a starter? What? That's electrical...

I agree though the gears are killing you. How you drive does too. I get my best mileage around 65mph. 410s and 33s. I can get around 18mpg hwy. 65 is enough rpm to pull grades while not working the engine harder to maintain a faster speed.
 
And in typical fashion you spout off some wild thing with nothing to back it up and nowhere to go with it. Maybe it needs a starter? What? That's electrical...

I agree though the gears are killing you. How you drive does too. I get my best mileage around 65mph. 410s and 33s. I can get around 18mpg hwy. 65 is enough rpm to pull grades while not working the engine harder to maintain a faster speed.


I post for the thinking people.

Across any Jeep board more than 60% of the complaints of failures are electrical, not mechanical.

I was referring to ignition/injection and sensor/sensor circuits primarily. And ground paths as well.


As of late I've been studying high-end audio, those are the guys to learn from. Those are the guys that use power, lots of power.

You might glean just a bit from this short exchange, last couple of posts-
https://comancheclub.com/topic/45526-before-and-after/?page=7


Efficiency or efficient is a foreign language on a Jeep forum.
 
the speedo gear will be dependant on tire size and your gearing iirc, so you will probably want to do that last. as doing it before the gear swap will leave you in the same boat as far as your milage being innacurate, i am not sure which temp sensor in the 96 you will want to clean. i cleaned both in my 99. i am about to regear as well, and have been fighting mpg also.

another thing i forgot to ask is if your exhaust manifold is leaking at all, i am pretty sure that will effect mpg also.

Youre right that totally slipped my mind, I should probably regear then swap my speedo gear...I should also clean both my sensor just in case, and since im trying to fight an overheating issue (have another thread on it). I never really checked for a leak, I just always assumed its leaking. Should start saving up for some headers and a high flow catalytic converter, that paired with my cherrybomb would be sweet!


With the plastic tank that's about right for the "low fuel" light to come on. I once ran mine down to 1/2 gallon!

Thats crazy! The max ive run it down is around 3.5 gallons and I was pissing my pants hahah didnt even know you could run them that low.

speedo gear
gearing
lose any roof rack
inflate tires
o2 sensors
use cruise control as much as possible

no roof rack, the thing already produces a ton of drag dont need more lol, tires are checked with every oil change so they should be up to spec. Waiting on complete exhaust overhaul for O2 sensors. Dont have the luxury of cruise control on my 96 lol

I'm becoming convinced that 90% of the complaints regarding MPG is due to a very poorly designed and poorly maintained electrical system.

I get what youre saying, somewhat. I also get what youre saying about efficiency, but thats a bold statement man, not exactly sure about the statistics behind it.

And in typical fashion you spout off some wild thing with nothing to back it up and nowhere to go with it. Maybe it needs a starter? What? That's electrical...

I agree though the gears are killing you. How you drive does too. I get my best mileage around 65mph. 410s and 33s. I can get around 18mpg hwy. 65 is enough rpm to pull grades while not working the engine harder to maintain a faster speed.

Wow, running 33s and getting 18 hwy is only a dream for me. Hopefully soon ill regear it and see what happens with my gas milage. On a side note: why did you choose 410 and not 456?
 
Had 4.56. loved it. Due to interesting circumstances, ended up with 4.10s. work well enough for my driving style that I never cared to spend the money just to go back up to 4.56. but if youre starting from scratch, 4.56 for sure.
 
I have a 93 xj no lift ax15 np231 with 33x12.5r15 tires as well. I don't have all the heavy stuff on there but I still have stock gearing as well. I have calculated that the tire size speed correction is that you add 11% to what your speedo says and that's how fast you are actually going. So in mine ill be doing 72mph and I'm actually doing about 80mph. The same calculation can be used on your odometer to calculate mpg. I'm currently getting 16-17mpg at mostly highway driving.
 
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