How does it do it?

[crashmarks]

While im in a posting mood. Can anyone tell me how the system measures the amount of fuel that is being consumed i.e. is there a device or sensor through which the fuel passes that measures the flow rate. I am particularly intrested if the system on my diesel is taking account of the fuel burned by the FBH.

[FrenchMike]

I guess the ECM compute from the number of milligram per stroke

All i know is the FBH consumes half a liter per hour at full load.
And that is a false economy to cut it;a quicker hot engine consumes less.

Mike

[T-Cut]

The OBD fuel consumption statistic is determined from the fuel consumed (via the tank level changes) and the distance travelled, since the last computer reset. In this way, fuel consumed by the FBH is integrated to give the effective mpg. In a similar fashion, it uses the same data to calculate the Range for the remaining fuel. It assumes your current mpg figure will apply for the rest of the tank. If you reset the computer too often, the figures will be very unrealistic. Best is never to reset at all.

TC

[crashmarks]

Cheers T-Cut.

[rossocorsa]

Originally Posted by T-Cut

The OBD fuel consumption statistic is determined from the fuel consumed (via the tank level changes) and the distance travelled, since the last computer reset. In this way, fuel consumed by the FBH is integrated to give the effective mpg. In a similar fashion, it uses the same data to calculate the Range for the remaining fuel. It assumes your current mpg figure will apply for the rest of the tank. If you reset the computer too often, the figures will be very unrealistic. Best is never to reset at all.

TC

Im not sure this is entirely correct the computer does take into account the rate of injection which is why the fuel consumption becomes over optimistic when a synergy is fitted because the ECU doesn't 'see' all the diesel that has actually been injected. I am not at all sure that the system compensates for the FBH but I have noticed that as the tank level reduces fuel comsumption readings do seem to alter a bit suggesting that it takes some account of tank level but I'm not convinced

[HarryM1BYT]

It counts the injector pulses and how long the injectors are open, which is why, when a Synergy is fitted (which alters the fuel pressure) - it can read a bit optimistic. Increased pressure, more fuel is injected for a given period of opening.

I'm under the impression that the average consumption is based upon the past x number of miles, rather than an average since the last reset.

Range is calculated from the above calculated consumption and the amoint of fuel in the tank. Adding more than a set amount of fuel to the tank, forces a recalculation of range.

Or at least that was how my previous car did it, but that also had an instantaineous fuel consumption reading, as well as the averaged reading.

[COLVERT]

Originally Posted by T-Cut

The OBD fuel consumption statistic is determined from the fuel consumed (via the tank level changes) and the distance travelled, since the last computer reset. In this way, fuel consumed by the FBH is integrated to give the effective mpg. In a similar fashion, it uses the same data to calculate the Range for the remaining fuel. It assumes your current mpg figure will apply for the rest of the tank. If you reset the computer too often, the figures will be very unrealistic. Best is never to reset at all.

TC

The computer in my wifes car must reset itself continuously because the read out of the distance left for the remaining fuel rises steadily before your eyes if the car is driven very gently.

[T-Cut]

Originally Posted by COLVERT

The computer in my wifes car must reset itself continuously because the read out of the distance left for the remaining fuel rises steadily before your eyes if the car is driven very gently.

That's because driving gently has a dramatic effect on the current (averaged) consumption figure. It's being artificially improved, so the range rises in real time. The thing is you're not likely to drive in that manner for the rest of the tank.

TC