I have a 2000 Mercury efi saltwater engine 250hp that is using well over a gallon of gas per mile-have changed all filters,high end fuel pump,strator and plugs-it seems to surge some at low speed and tops out at 5100 rpms now-had both oil and fuel filtered-any help would be good-thank you,David

replace front fuel pump because gauge is made into fuel pump and not serviceable. Or poor boy way of getting by would be fill front tank with gas reset mileage drive normal for a day. refill again with gas note gallons used and mileage driven for average miles per gallon. front tank should be around 17 gallons multiply by mile per gallon you figured

use higher octan gas to see change air filter oil change will allway in most cases give a few moe miles on the gas

try by changing the fuel filter. if the other stuff works ok then the engine is being starved for fuel during high speed use.... Could be debris in the fuel system.

What grade of fuel are you using? There are many conditions that effect gas mileage. The way a vehicle is driven, is it shifting correctly, flooring it to get up to speed from dead stop also known as Jack Rabbit starts, driving with the defroster on when it isn't needed or the setting just above that can be used. Back in the 90's most car manufacturers made a change to their heating.cooling system that caused the AC compressor to kick in when the selector was set to defrost. This puts drag on teh motor and decreases gas mileage. Build up on valves and low compression in the firing cylinders will cause you to lose gas mileage as well. Do a compression check on the motor to make sure you don't have abnormally high compression or low compression on cylinders and use a bottle of gas treatment in your fuel to clean some of the carbon build up from injectors and valves. Also start using the Mid grade fuel. Not the High Octane in your area. In Texas we typically have 3 choices 87, 89 and 93 to choose from. Low grade is enough to run the vehicle but performance is low as well as mileage. I use the 89 octane for better performance and better mileage. The High Octane or 93 isn't really good as it leads to higher carbon build up on the valves. Also check your oil often and make sure your changing it every 4000 miles at the longest. All of this along with making sure you change the Air Filter every 5000 miles will increase your mileage.

I think the mileage is just about how you can control yourr driving methods. I am giving below a link for tips on getting better mileage.

http://www.fixya.com/cars/r6019480-tips_fuel_saving_hypermiling

You can also check the tuning of the car, check for timing/ pump calibration as your car is working fine otherwise.

For the 6 cylinder 4.0 Liter EFI (electronic fuel injection) SOHC (single overhead cam) engine
(8th digit of VIN = "E"), and
the 8 cylinder 5.0Liter EFI engine (8th digit og VIN="P"):

1. relieve fuel system pressure
2. remove/disconnect:
NEG. battery cable
bolts holding fuel filter shield
fuel lines (3 of them) - labeled (1) in above diagram
fuel filter (labeled (2) in above diagram - from its support

Installation is the reverse of removal, but torque the fuel filter shield bolts to 15 ft-lb. (20 Nm).
And, if you're as careful as I am, apply anti-sieze to the bolt threads before they go in.

Your gauge is reading high ... I think you are out of gas. You should calculate your actual Miles Per Gallon - find out what the capacity of your tank is and fill accordingly. For esample, you actually get 15 miles per gallon, your tank is 20 gallons - you should be able to drive about 300 miles between fillups. At 250 miles, start looking for a station.

Your car should average roughly 32.5 mpg-US (7.24 L/100 km; 39.0 mpg-imp)

Have you changed the fuel filter? I know it sounds weird but a plugged filter will make a truck use more gas. The computer tries to compensate for less fuel by commanding the injectors to open longer. Also a plugged filter will cause excess back pressure on the fuel pump making it loud.. Good Luck.

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