Poor milage

[gageanimal]

Have a 98 Grand Cherokee 4.0 4x4 once engine reaches operational temp gas milage drops off to 11MPG...where do I go other than the gas station everyday?

 

[TerryMason]

Welcome to Jeepz.com
Is your check engine light on, and are you able to pull any codes?

To pull the codes, just put the key in, and turn it from off - on - off - on - off - on, then the codes (if there are any) would be shown on the odometer.

 

[98Chero]

:welcome: MPG depends on how you are driving it. If locked in 4x4 all the time 11 mpg sounds right. if driving it in stop and go traffic with the AC on.. again thats about average. The average 4.0 L engine highway miles in 2x4 should be around 18 mpg. You might need to check and replace.. Air cleaner, Fuel Filter to really know whats going on.

I hope this helps

Mike

 

[mark sr]

How long have you had your jeep? Is it all wheel drive? Are you figuring the mpg by dividing gallons/miles or just going by the readout on the dash? The 1990 cherokee I used to have averaged 18 mpg with the 4.0, don't think it ever dropped below 16.

 

[superj]

all our 4.0 jeeps always did well, also. I would say something needs some work

 

[JPNinPA]

Have a 98 Grand Cherokee 4.0 4x4 once engine reaches operational temp gas milage drops off to 11MPG...where do I go other than the gas station everyday?

One is validate mpg by a fill up. Reset trip odometer and drive until you are near empty and refill to the same tank level. (one click, squeeze a bit or fill till it overflows.)
Use thr miles driven by the actual refill gal. If you only go to a quarter tank or 100 mi... There is too much error by how you refill and will result in up to 25% variation in mpg.

Do you have the correct speedo gear? If your speed is off due to tires and gearing your mileage is off.

Any gas leaks? Does your vehicle smell of gas during or after driving? Leaky lines under pressure even a stuck open injector can lead to issues.

What does your engine idle at? Intake and exhaust leaks can cause the PCM to increase the fuel to air ratio.
Bad O2 sensor(s) bad CAT(s) or dirty intake and TB dirty air cleaner or restricted air flow.

Other things
Dragging break
Out of alignment
Improperly inflated tires
Heavy pedal
Excessive idling - red lights stopping all the 0mph time and how fast you start back and stop.
How fast you drive 10 mph or 70?
Is 4wd engaged?