• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

very poor fuel mileage

ruger81

ruger81

NAXJA Forum User
Location
Battle Ground WA
been battling this for months i have replaced CTS, MAT theromstat, cleaned the ccv system sea foamed the intake, no codes cant figure it out i filled up with 92 drove 27 miles fuel gauge is almost reading 3/4.. terrible has anyone else had this happen. this jeep used to get atleat 18 miles per now its maybe 10 if im lucky.. it run's awesome no smoking no rough idle..
 
Re: very poor fuel milage

Why would you use 92 octane ? 87 is all you ever need.

How many gas tank fill ups have you calculated to determine you have low gas mpg's ? The gas gauge is not calibrated, nor is it graduated to show how many gallons are present, it a more/less indicator, as in you have more or less gas than the last time you looked at the gauge.

Are all your tune-up parts fresh ? How about the air filter ? Is your speedo output adjusted for your tire size/gearing or do you allow for any odometer error in your mpg calculations ?
 
Re: very poor fuel milage

the reason i filled with 92 is cause i heard of some people getting better fuel milage by using better octaine fuel. my speedo is correct. i think i have a garmin that has a speed display and a speedo check tool. also all the tune up parts are less than two months old maybe 500 miles. how i check the mpg's is i fill up and drive press reset on the trip drive 50 or so miles get more fuel take the miles drivin diveded by the gallons used since i have had this prob its been aroun 9 or 10 per gal wich sucks bad. last winter i got at least 15 to 18..
 
Re: very poor fuel milage

while a 25%-50% decrease in mileage is probably enough for anyone to notice without even doing the math, I agree that the 50 samples are too short to get any useful data. In 50 miles, your results can be skewed a lot just by the "cut-off" point on the dispenser (pump).

Keep a log and record at least four tanks worth of data-- you'll get a better idea of what the Jeep is doing with fewer chances for erroneous results.
 
Re: very poor fuel milage

Mr Obvious here!

But i have to ask.
Have you checked for any gas leaks from tank or fuel lines?

Another quick ques. Whats your jeep's operating temperature?

You do have any evidence engine is running rich? (other than mpg)
 
Re: very poor fuel milage

Check your manifold for cracks and replace your upstream O2 sensor. Also have you replaced the plugs, cap, and rotor? I had a noticeable throttle response improvement and likely fuel mileage (haven't gotten enough miles on it to know for sure) improvement just replacing the plugs wires cap and rotor on my 91... long overdue at 230k.
 
Re: very poor fuel milage

clean96XJ said:
Mr Obvious here!

But i have to ask.
Have you checked for any gas leaks from tank or fuel lines?

Another quick ques. Whats your jeep's operating temperature?

You do have any evidence engine is running rich? (other than mpg)
Click to expand...
yes i have checked.

the operating temp is 210

it really reaks towards the tail pipe
 
Re: very poor fuel milage

kastein said:
Check your manifold for cracks and replace your upstream O2 sensor. Also have you replaced the plugs, cap, and rotor? I had a noticeable throttle response improvement and likely fuel mileage (haven't gotten enough miles on it to know for sure) improvement just replacing the plugs wires cap and rotor on my 91... long overdue at 230k.
Click to expand...
no cracks I just did a complete tune up ( plugs,cap,rotor,cleaned KN, fuel filter) around 500miles ago

the only thing i havent done is new map sensor and new o2 sensor!
 
Re: very poor fuel milage

thank you all for your responses keep em coming please there has to be someone that has had this problem.
 
Re: very poor fuel milage

I take it your were getting much better gas mileage, then it dropped, with no changes to the jeep?

I see a lot of gas guzzling Mods on your list, if that is the rig your talking about?

My mileage increased at least 50% when I replaced the O2 sensor. :D

You can test the O2 sensor live!!!!
 
Re: very poor fuel milage

Everybody complains that computers have made it too hard to work on vehicles. It is too hard because people rely on them too much. Being old school, the first thing to check is to do a spark plug reading. Follow that by looking at the tail pipe. Is it real black and sooty? Does it sound kind of thready and the tail pipe has a kind of whistling sound? If you bang the CAT does it rattle?
 
Re: very poor fuel milage

Ecomike said:
I take it your were getting much better gas mileage, then it dropped, with no changes to the jeep?

I see a lot of gas guzzling Mods on your list, if that is the rig your talking about?

My mileage increased at least 50% when I replaced the O2 sensor. :D

You can test the O2 sensor live!!!!
Click to expand...
your right it was the first thing i did was change to 410 gears to try and get the gear closer to the tire.. it seemed to help alot then all of the sudden one day it dropped in half..
im gonna test the o2 sensor tonight all report back.(there are no codes)
i just went out to the interstate and ran the speedo check station its 1tenth off in five miles.. 4.10's are for a 32in tire im running 33's
 
Re: very poor fuel milage

old_man said:
Everybody complains that computers have made it too hard to work on vehicles. It is too hard because people rely on them too much. Being old school, the first thing to check is to do a spark plug reading. Follow that by looking at the tail pipe. Is it real black and sooty? Does it sound kind of thready and the tail pipe has a kind of whistling sound? If you bang the CAT does it rattle?
Click to expand...

i kinda like the whole computer thing it gives you a solid place to start.
the spark plugs are perfect per the chilton manual picture i can post one if you like.

its black and sooty smells like gas.. stains ur fingers bad!

no noise no rattle used a dead blow!
(Does it sound kind of thready and the tail pipe has a kind of whistling sound?) please explain better im not understanding..

thank you all for the post's i cant wait to find out the prob.
FYI(tonight i drove 108miles stopped and filled up 10.1 miles to the gallon..)
 
You must log in or register to reply here.

Similar threads

C
91 XJ missing at 2000 +rpm only when at operating temp
Replies
0
Views
1K
cptmiker
C
W
Build thread: daily driven tow rig
4 5 6
Replies
117
Views
10K
Woodswanderer
W
D
Troubleshoot my troubleshooting RE:poor fuel mileage
Replies
9
Views
1K
Hypoid
Hypoid
J
99 Running very rough
Replies
12
Views
661
jeffreylane
J
xjtrailrider
1994 with poor fuel economy
Replies
13
Views
1K
xjtrailrider
xjtrailrider
Back
Top