True Ltr/100Klm Calculation? - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

scruba · 03-10-2005, 01:44

How is the true Ltr/100Klm calculation worked out on cars not fitted with a trip computer?

I guess it can only be carried out on a full tank of fuel and then at the refill what has been used in ltrs is divided by the klms driven. Is this correct?

81foXDwagon · 03-10-2005, 03:18

I wouldnt trust the trip computer that much.

It works out your L/100km based on how many injector pulses are fired over the course of km travelled. The flow given by an injector pulse just follows an equation that says X amount of fuel goes through with injector pulse length Y based on the injector characteristics.

When the injectors get blocked / old, the injector characteristics will change. Over the course of many km, this can give you a false economy reading.

Ive always worked it out starting with a full tank of fuel, running it to the same point (just under 1/4) then filling up:

Economy(L/100km)=Fuel(L)/(KM travelled / 100)

fordboy98 · 03-10-2005, 14:49

All good points about the injectors. On my EL XR6 5-sp I compared the trip comp against a manual calculation for fuel usage on the same tank of fuel. That is, I ran the tests simultaneously. Full tank, zeroed the TC and trip meter and away I went on a country trip. After I'd carefully refilled and punched a few buttons on the calculator, I found that there was only 0.2 L/100k difference between the two. I thought that was pretty good, and good enough to believe the TC for all practical purposes.

scruba · 03-10-2005, 17:38

Cheers.

I've been getting odd numbers lately.

7ltr/100, 12ltr/100, 10.2ltr/100 etc.

Weird. Maybe the odometer is out?

sleepwalker · 03-10-2005, 21:42

fill it up to the top, drive around for 100k's and then pull into servo and see how much you need to fill up again.