1999 Ford Expedition new engine uses twice as much gas

Any codes?

You have it backwards

What you hear is engine noise from
higher rpm, because your trans is not
upshifting, as a result of your input on
the gas pedal

You need to have a trans or repair shop find out why
you have a delayed or no shift condition

When you get to 4th or 5th gear (overdrive) you also
get torque converter lock-up & things should get quieter

As these are two different motors with different type control systems involved, did you mean that you installed a replacement motor that was remanufactured or purchased new in 2005?

The tune-up is a Fred Flintstone term,
meaning you got spark plugs or payed
for them and got nothing

You need new spark plugs
You need 2 new front O2 Sensors, if you
have 100,000 miles on them
You need the MAF Sensor Cleaned
A Clean Air filter
Correct fuel pressure
A properly working TPS Sensor
(throttle position sensor)
And other items.

See if you have all that done, and get back
I will evaluate your issues.

Do you have check lights on the dash
If so give us the codees

At today's gas prices, if you reside in the USA, that's only about 10 gallons of gas. If you've got a carbureted v8 engine in a 38 year old truck, you should be getting around 11 mpg. Probably less with stop and go driving. You did not say how many miles you drove for the 30 dollars worth of gas, but if you got a hundred miles, that would be just about right.

on normal that trk should be around 6-7 gallons used per one hundred miles drove. i based that at 15 mpg. now that is also based on a V8 engine. now 1 gallon of gas is 3.78541178 liters which totals 12 galons of gas to 45.42494136 liters. This would mean that it took 12 gallons of gas to travel 100 miles which totals 8.3333333333 mpg. not as good as i would have thought. 8 miles per gallon (mpg) hell that engine must be a big block 460. If it is that big cubic inch i could understand but any other motor should do better mpg than 8.3. so i agree that is not normal, tune up, or look for fuel leak in the fuel supply or( feed ) line. From the tank to the motor. This must be a canadian truck yes? well hope for the best or trade that guzzler in for a new breed. stay warm!

It could consist of skipping, engine cutting off or hesitates from starting, idling . Bad gas gives numerous signs, the best way I have found to deal with this is, Buy a octane booster 104, go to the gas station and put a couple of gallons of high premium in to tank to disperse the water in the gas. They also make a liquid to take water out of gas which also goes into the tank.

Check the code and see which cylinder is the one that is missing.Then remove that coil and check the plug.The coils are known to go bad on these vehicles.To make sure you can swap it with another coil if the misfire changes to another cylinder then replace the one that is causing the misfire.Hope this helps.

go to autozone for a free computer scan and get the fault code. Possibly one of the COPS, Coil on Plug. COde will tell you

The 99 expedition comes with a 26 gal tank as standard equip. and there is an optional 30 gal available. I suspect the gas pump you used is not accurate, and needs to be recalibrated. I think it's just a coincidence that the gauge is acting up now. Hopefully I'm wrong, and by some miracle you actually are now getting 300 miles on a half tank of gas! You may have a bad sending unit, this would result in inaccurate fuel tank readings.