My 4 guesses are:

1. Fuel leak

2. Running too rich

3. Someone is swiping fuel from the tank.

4. The station where you buy gasoline has an erroneous meter on the delivery pump.

A fuel leak could be anywhere in the fuel system, but then, you would probably smell it, so I am excluding this one at the moment. The probability of items 3 and 4 are low. This leaves #2 as prime suspect.

Look for things that can cause over-rich running. With the mileage drop you report, the sparkplugs should show black soot. One possibility is that the system is staying in the default start mode and never gets around to controlling the fuel mixture via the oxygen sensor.

The vacuum may be low while crusing causing retarded spark. A partially clogged catalytic converter can casue this.

Diagnostics by a qualified technican can answer a number of questions and eliminate a lot of guesses.

High fuel consumption,, is this measured over a couple of tanks of fuel, or simply happen on just this one?

The valves are hydraulic, there is no adjusting to be performed.

If it was running too rich it should be setting a trouble code and a check engine light.

The computer systems are pretty smart. if the convertor was plugged up, the onboard computer would actually detect that the MAF sensor is under-reporting airflow through a volumetric efficiency "VE" calculation. Now it would turn the MIL on and set a P0101 for MAF sensor performance because it would not know why the "VE" was incorrect but it would recognize this.

If the emergency brake isn't releasing fully, that could seriously impact fuel useage.

If you ahe been looking at this from a single tankfull, it could be the gage is doing something erratic.

A fuel leak again is extremely unlikely, first you would smell it, secondly the evaporative emissions system would detect the leak and turn on the MIL (check engine light).

As far as someone stealing the fuel, there is a roll-over valve, and the car also uses ORVR, On-board Refueling Vapor Recovery which between them make it virtually impossible to siphon a fuel tank. It's a real PITA when I have to service a fuel pump, not to mention a great saftey hazzard dealing with a full fuel tank that I cannot drain.

The car already uses platinum plugs, in fact they should be double platinums. If there is a missfire occuring, the car would detect it and agian illuminate the MIL.

It would be a good idea to get this checked, first of all it's still under the 3year- 36,000 mile warranty. One possible cause could be that the vehicle may have been fueled with E-85, and may not actually be a flex fuel truck. Although I would off-hand expect that a 3.0 Ranger would be a flex fuel, and quite capable of handling such fuel. If a problem in the feedback system occured at just the right time, the vehicle could be totally confused thinking it got refueled with E-85, when in fact it actually got regular fuel. It would take it a while to figure out that something is amiss if that was to occur. A qualifed tech, with the correct tools will make easy work of verifying the engine control system. Since this should be still under warranty, a dealer is where to go. After that if you want to go somewhere else find a shop that has invested in the Ford IDS scan tool, and is not just relying on some aftermarket 1/2 tool.

Thanks all!

No. On a trip I just noticed the odometer meter flip over into a row of zeroes and my tank showed exactly half full. On cruise and having nothing to do but steer I decided it was good time to check the consumption, so I watched my reading until I got exactly 1/2 of a quarter tank, then I noticed it ran 63KM.

Knowing I have a 20Gal tank, it didn't take long to figure that it drank a lot of gas. Regardless of the method used to figure it out, those facts glare out pretty obvious.

If I deviated a bit, then I could chalk it up to maybe the fuel sensor in the tank that's bobbing up and down or hasn't righted itself just yet, or some other reason that makes it not an exact science. But this much difference got me concerned.

I've got an appointment on Monday and I'll have the shop check to see if everything looks OK.

Can't expect too much enthusiasm on Christmas eve.!!

AndyF

OK I see the problem..

>No. On a trip I just noticed the odometer meter flip over >into a row of zeroes and my tank showed exactly half full.

You are "assuming" that a fuel gage operates in a perfectly linear fashion. It doesn't.

>On cruise and having nothing to do but steer I decided it >was good time to check the consumption, so I watched my >reading until I got exactly 1/2 of a quarter tank, then I >noticed it ran 63KM.

The only real way to check fuel consumption without some really trick equipment (The Ford IDS scan tool) is to fill the tank, and record the odometer reading. Now drive the vehicle, and when you fill up again find out how many miles you went and divide that by the gallons consumed. At this point you don't really know how much fuel was consumed for the gage to move that far. You really don't know if it was displaing exactly how much fuel was in the tank when you started your test, nor when you ended it.

BTW, not operating exactly linear is not a problem that needs fixed either. It's actually a typical strategy to make the gage move faster as the fuel gets lower which makes it more likely that the operator will fill the tank sooner.

You can cancel the appointment, there is nothing for them to find.