Fuel usage calculator

[ClintJ]

Originally Posted by Philster

Bear in mind that you need to measure not only how much fuel is going to the pump, but also subtract the quantity coming back through the return.
If I understand it correctly, the only alternative would be to derive the total from the injector open timings.
I believe fuel is returned from both the pump itself and from the injector lines, so it may be necessary to to rather a lot of measuring
Better check the fuel circuit flow with Bob, ClintJ, or another expert to be safe.

Measuring delivery would tricky. Have a look at some scope samples below.
the pink line is the spill valve and the white sine wave is the pump reference.
the pump reference is a 360deg toothed cog with a change in patern every 90deg to help for referencing the camplate in the pump and for cross referencing the TDC signal that comes from the crank.
If you knew exactly how much the injector flows at what pressure then you could reference the spill valve to calculate how much is being injected.
It sounds like a big job but if the prof is keen then best wishes!!

[theproff]

I have done this on a diesel 306 before, using the same method Philsters suggests I attached a flowmeter to the outward bound fuel pipe, and another to the return pipe back to the tank.
i also connected an infra-red device to the speedo cable which sends 8 pulses per revolution to the micro.
the software simply counted the pulses from both flowmeters every second, deducted one from the other to give pulses/fuel used. the flowmeters were calibrated to less than 1%, with the speedo IR device a pretty accurate MPG was achieved.

very simple process, i used a 2 digit display to show MPG. i have also been thinking of using a GPS OEM Module to give the speed, rather than the IR device, but these will shoot the cost up, but could give added functionality.

I have been looking on the forum to see if the Estima's use the same principal for fuel delivery and return, to no avail yet.

thanks tony

[Philster]

There are fuel return pipes from the injector nozzle spill pipe and from the pump - you would need to either combine these (if they don't already) and measure the return on the tank side of the junction, or measure both (and deduct the sum from the feed).
I believe there is a minor modification which feeds the return into the inlet, instead of back to the tank, helping to heat the filter for using veg.
If this mod includes both returns, it would simplify matters, as you would only need to measure at a point between the tank and the point where the return is fed back in before the filter. That might have a slight delay though, as it is rather a long way upstream, and the flow may lag a little behind the demand due to fuel contained in the pump body, filter housing, and pipework.

I think that a single measure of the combined returns subtracted from the pump feed would give a good combination of responsivity and accuracy.

GPS calibration would be a bonus, although I've set my speedo by a GPS already, I know that many haven't (possibly an upgrade option?).
My odometer is accurate according to the marker posts on the M11

One slight warning - any bus with a speedo chip to convert from KM to miles will be throwing away 3 out of 8 pulses, so you may need a jumper or dipswitch to allow for that.

After the recent messing about changing fuel tanks, I should remember whether the returns are combined before going back into the tank, but I'm afraid I don't.
I think there's just one going back into the tank, but I'm not sure - I'd want to check to be sure (or even better, ask Bob, 'cos I'm less than confident of my ability to correctly identify all the pipes and hoses).
I do know the fuel consumption is abysmal if a return pipe comes off the tank fitting, and the back of the bus gets very oily

[theproff]

thanks for all that info Philster, i will put a new thread on the forum and ask people about the fuel return.

GPS can be made an option to the design, it will be the first one i design as its the one i personally want.

cheers. tony