I haven't posted in awhile because I have had no problem with my 98 Grand Cherokee Laredo 4.0L. However I have moved from my hometown which is right outside of Philly to a high elevation in State College (I am a Penn State Student). I've noticed that my gas mileage on my Jeep has steadily declined when I moved up here. Some one told me that it is because of the high elevation that I am not getting the gas mileage that I should be (I used to be getting about 14 or 15 mpg around town and now I only get about 10 mpg). I did do a tune up and replaced the distributor, cap, pick up, rotor, the best spark plugs that Advanced Auto had (Bosch Platinum IR Fusions), Autolite Professional Series wires, new fuel filter, installed a K&N air filter kit, changed the oil and filter and flushed the tranny and coolant system. After doing ALL OF THAT, my gas mileage still sucks. Tires are also inflated correctly too. Is there anything else that I could do to increase my gas mileage?

The colder weather that we are slowly getting into will eat up more gas. You can check for a stuck brake caliper and a toasted viscous coupler if you have a quadra-trac case.


I haven't posted in awhile because I have had no problem with my 98 Grand Cherokee Laredo 4.0L. However I have moved from my hometown which is right outside of Philly to a high elevation in State College (I am a Penn State Student). I've noticed that my gas mileage on my Jeep has steadily declined when I moved up here. Some one told me that it is because of the high elevation that I am not getting the gas mileage that I should be (I used to be getting about 14 or 15 mpg around town and now I only get about 10 mpg). I did do a tune up and replaced the distributor, cap, pick up, rotor, the best spark plugs that Advanced Auto had (Bosch Platinum IR Fusions), Autolite Professional Series wires, new fuel filter, installed a K&N air filter kit, changed the oil and filter and flushed the tranny and coolant system. After doing ALL OF THAT, my gas mileage still sucks. Tires are also inflated correctly too. Is there anything else that I could do to increase my gas mileage?

Only thing you can do is check for fault codes.
I lost about 1.5 mpg around the beginning of the year, from 13 - 12.6 mpg to 11.5 - 11.6 mpg (all city). I have yet to figure it out.
If you find the answer let me know!

I haven't posted in awhile because I have had no problem with my 98 Grand Cherokee Laredo 4.0L. However I have moved from my hometown which is right outside of Philly to a high elevation in State College (I am a Penn State Student). I've noticed that my gas mileage on my Jeep has steadily declined when I moved up here. Some one told me that it is because of the high elevation that I am not getting the gas mileage that I should be (I used to be getting about 14 or 15 mpg around town and now I only get about 10 mpg). I did do a tune up and replaced the distributor, cap, pick up, rotor, the best spark plugs that Advanced Auto had (Bosch Platinum IR Fusions), Autolite Professional Series wires, new fuel filter, installed a K&N air filter kit, changed the oil and filter and flushed the tranny and coolant system. After doing ALL OF THAT, my gas mileage still sucks. Tires are also inflated correctly too. Is there anything else that I could do to increase my gas mileage?


Checking for fault codes is a good idea. I can tell you that I live at 220o ft above sea level, the higehst point in the Poconos and I have owned a 91 Cherokee LTD with 4.0 and it did get 15 up here. Now I own a 94 G Cherokee Laredo with the V8. I just bought this to restore and have done a LOT of work on it the past couple weeks. One thing I had wrong was the O2 sensor was shorted. Prior to replacing that I was getting 14 MPG. The mileage jumped to 17.5 after replacing the O2 and that is with abad Viscous Coupler ( next to go ) in my transfer case.

My vehicle will spit out the fault codes by tunring the ignition switch on then off, on then off then on. The check Engine light will flash a morse type code. lets say 2 flashes, a pause then 1 flash. That is a code 21. A code 55 is the end of cycle and the exit code then it will start all over again.

Sounds like you went the right route anyway with a QUALITY tune up, so if your tires a good and ignitiaon is up to snuff, I would suspect an emissions control or possibly an injector problem. I firmlay believe in running injector cleaner in my fuel tank every 4th tankful.

Good luck and lets us know what you find. :smokin:

I'd like to add my 2 cents to this thread. A couple years ago I bought a cheap performance chip for my Grand Cherokee. It spliced into the Intake air temp sensor. It fooled the computer into thinking the air was a different temp than what it really was and increased HP by ramping the air/fuel mixture... On I-25 (here in colorado), my MPG jumped from 18-19 MPG to 23-23 MPG at 75 mph... I was pretty impressed... then one day my cars MPG's dropped dramatically. Turned out the performace chip fried, and took out the temp sensor with it... I'm not saying this is your answer, but i'd look at maybe replacing it, or cleaning it at least to see if it helps any...

Thanks for all the replies guys. One thing I did not replace when I tuned up the Jeep was the O2 sensors. I will definitely check them out. And today I just thought about how the Temp sensor could also be bad. Thanks a lot guys. I will let you know how I make out.

So I am in the process of getting my VC replaced, had the locking wheels after hot causing the crow hop into parking spots.

Tossed around the idea of buying a recharged unit from some company in CA. Apparently they can drain and refill the silicone fluid that goes bad but nothing else is touched, to my understanding. At 200.00 per unit it sounded like a good way to go, hwoever after reading an article on Rockland Standard Gear on the NP249 and finding out that the seals inside the VC go bad I decided to spend an extra 130 to get a new, updated version of the NP249 coupler. I do not want to be doing this again next year.

Alos note that a bad VC will put a major pounding on the front diff and can cause it top fail. If you got wheel hop on tight turns, fix the VC before it costs you even more.

Jaz1314 94 JGC Laredo nickname "Frankenstein":smokin: