Fuel metering for fuel economy calculator? - Ford Powerstroke Diesel Forum
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Old 02-03-2009, 12:26 PM
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Fuel metering for fuel economy calculator?

My truck (2002 F-250 Lariat) has the fuel economy calculator in the over-head console. My question is, where/how is the fuel metering performed? I assume its not a flow detector pre-fuel bowl as the fuel bowl has the return path from its regulator ... is it calculated based on injection parameters (pulse-width, fuel press, HP oil press)?

What I am trying to get at is ... is a fuel leak at the fuel bowl contributing to a lower _displayed_ number? Or, is the way it is measured not affected by this fuel leak? I'd appreciate a response from someone who knows the specifics ... because this can be calculated in a way that both is affected or is not affected by a fuel leak.

Thanks.
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Old 02-04-2009, 11:03 AM
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There is enough information in the computer to determine the best guess at fuel rate. The fuel rate is then compared with speed to get mpg. The fuel rate that is commanded by the computer is what is being used for mpg so in the event of a leak of fuel anywhere the reported mpg would be higher than actual so long as pressure is maintained in the fuel rail. Meaning, so long as the fuel pump can keep up with the leak, the truck won't know that there is a leak and won't account for leaked fuel.

If the pump can't keep up with the leak then you should see your fuel level dropping on the gauge right before your catastrophic fuel leak causes a wreck.

I use the scanguage and find it to be fairly consistent once calibrated. I would gamble that the ford computer is the same thing with a fixed calibration.
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Old 02-04-2009, 01:39 PM
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I though it just based it on throttle position.
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Old 02-04-2009, 03:36 PM
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Throttle position sets the volume of each squirt but RPM determines how many squirts per second. Both are monitored and combined with miles per second to provide a fuel rate per mile. The trick with our funny fuel injection system is that the throttle position doesn't directly move a rack on an injection pump so there is a calibration.
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