BAD GAS MILAGE

Hi Richard:
If there is a lot of pitting or corrosion visible, it would not hurt.
Replacing the spark plugs and air filter would help.
Changing engine oil and oil filter may not help with milage but it will make the engine last longer.
Increasing tire air pressure to the maximum rated for the tires will usually result in better milage but may actually increase tire wear rate.
Cheers

try changing fuel filter and making sure tire pressure is correct keep your car clean so air can flow freely and try an oil change all these factor into good gas mileage and you could try adding new plug wires to your tune up

• Replace spark plugs
  

• Replace rotor
  

• Check distributor cap (replace if necessary)
  

• Check timing (adjust if necessary)
  

• Check ignition wires (replace if necessary)
  

• Check ignition performance (firing voltage and ignition patterns)
  

• Check idle speed (adjust if necessary)
  

• Check choke (carbureted engines)
  

• Clean fuel injectors
  

• Check compression and/or power balance (identifies bad fuel injectors as well as compression problems)
  

• Check manifold intake vacuum (reveals exhaust restrictions)
  

• Check battery/charging voltage
  

• Check exhaust emissions (verifies fuel mixture, ignition performance and emissions performance)
  

• Check vehicle computer for trouble codes
  

• Install new air filter
  

• Replace fuel filter
  

• Replace PCV valve
  

• Check all emission controls (EGR valve, air pump, etc.)
  

• Check all vital fluid levels (engine oil, transmission fluid, coolant, brakes, power steering)
  

• Check belts and hoses
  

• Check safety items such as lights, wipers, tires (including inflation pressure), horn, etc.
  
  

the fuel pump will not cause bad gas mileage.the spark plugs may need changing,fuel filter,air filter,plug wires(basically a tune-up),or the thermostat probably needs changing as this can cause poor gas mileage as it won`t allow the motor to get to proper operating temperature(computer monitors temp)and commands fuel injectors on longer(spray more fuel).driving habits change over time look at this also.cold whether driving also will use more fuel.pcv valve i can`t help you,maybe a parts store will show were it is if it has one.the only time you change the fuel pump is when it gets noisy or it quits altogether,or the pressure is good but the fuel volume is not to specs.

COMPLETE TUNE UP SPARK PLUGS, WIRES, AIR FILTER, FUEL FILTER, OIL AND OIL FILTER, ADD INJECTOR CLEANER TO YOUR GAS.

Bad fuel, dirty fuel filter, dirty air filter, dirty injectors. I'm assuming there's no check engine light on. You should get upwards of 20mpg easy. try replacing the airfilter and fuel filter. I would get a K&N airfilter, i've had great luck with them. you should notice amore power and better fuel efficiency. Also, use an injector cleaning additive, like Lucas, and use synthetic engine oil. it cost more, but you'll change it less often and it's worth it. I'm a fan of valvoline. oh, and make sure your tires are inflated properly, that can make a noticeable difference

Tune Time.
1)new spark plugs properly gapped.
2)new air filter (check every 35000 miles)
3)new fuel filter (every 35000 miles)
4)1 bottle of STP fuel treatment (red bottle) 4x a year.
5) oil and filter change (castrol or another good quality oil every 3-4000 miles.
6)proper air pressure in tires (check every 2 months
7) service transmission every 40000 miles or less.

New oil and filter
8) new plug wires every 80000 miles.

try changing spark plugs,servicing the fuel system, air filter,ignition system,oil and filter.try doing a compression test to see how the engine is doing

usualy it is 20 miles to the gallon and to improve your gas mileage i would do a tune up... spark plugs, wires, cap, rotor, fuel filter. and add tune up in a can its only like $4.00 from autozone. and also replace your airfilter, add air to your tires like 35 psi. and clean your fuel system .

My Answer:

Poor gas mileage can be a result of many many things.

First of all you need to find out what is the factory normal gas mileage for your model year Jeep SUV. It should have said on your window sticker if you bought it brand new. If you are a 2nd or 3rd owner then a Jeep dealer would have info. Google search will tell you as well, and only takes a couple minutes to find.

I did a quick Google search and for a 2003 Jeep Grand Cherokee with a (4.7L V8 engine) the average mileage is roughly 14 mpg.

Not sure what engine you have as to options, etc?

How you drive will greatly change that number up or down depending on a number of driving and driver variables.

A few being -

Driving habits?

Tire pressures?

Engine tuned up?

Lube & oil/filter changes (every 5,000-7,500 miles? Air filter changes (every 10,000-15,000 miles)? Read your auto manual for exact recommended intervals.

How many people in the SUV on average?

Are you towing anything?

Type gas you are burning - BRAND? (See injectors below)

Area you are driving in (hills and valleys verses flat out,
etc)

Jeeps in general don't have a good track record for great mileage, and rough engine idling is always a clue that your fuel injectors are dirty. Typical on all Jeeps with port fuel injection systems! On Jeeps with dirty fuel injectors your mileage will go way down accordingly. If your not putting at least a 12 oz bottle of say Walmart brand Super Tech Fuel Injector Cleaner (~ $1 each) in your gas tank religiously every logged 1000 miles, or every 2 tank fill ups, then you are just inviting dirty fuel injectors and POOR fuel economy!

My 1993 Ford XPLR with a 4L V-6 engine (and ~ 160,000 flawless driven miles) gets roughly 22 miles per gallon on the highway with cruise control on, and about 17 around town on average. I religiously put a 12 oz bottle of the above injector cleaner in my gas tank every 1000 miles!! Of course I do all my own tune-ups, general repairs, and suspension maintenance (shocks, O2 sensors, trans oil changes, lube & oil/filter changes, code reading and clearing, etc) myself and it shows! I don't trust repair shops except for say Tires and Balancing at SEARS.

Hope that helps ease your mind about gas mileage as it relates to your Jeep there.

Frank