bnoble

I haven't been able to find definitive information on calculating fuel consumption using datalogs from a '730 (or any) ECM. I do a lot of commuting every day, and I'd like to be able to have instantaneous, and perhaps averaged fuel consumption available to keep my driving habits 'in check'

Basically I'd like to have at least instantaneous fuel consumption available while datalogging with the 730 ecm using tunerpro. The ALDL definition I'm using (from the tunerpro website) has provisions for a "Running Total Distance Travelled", that might come in handy for this, but it doesn't appear to be working correctly. I think that instantaneous fuel mileage could be determined fairly simply by comparing injector pulsewidth, rpm, and vehicle speed, but I'm unsure exactly how to determine fuel flow in lbs/hr using injector pulsewidth. I'm still trying to find answers to these questions:

Does an injector rated at xxlbs/hr flow at that rate under 100% duty cycle, or some other maximum recommended duty cycle, like 80%, since 100% should never be reached?

At 100% duty cycle, would the injectors essentially remain open at all times? Or is there some other cutoff point at which the injectors are considered saturated?

Since this is a batch fire system, each injector is firing at the same time. To calculate the total amount of fuel flowing past all the injectors you could simply pretend you had one injector and multiply the measured pulsewidth by 8. But since we're dealing with a 4-stroke engine, is the effective (single-injector) pulsewidth for one revolution of the engine BPW * 4 or BPW * 8? Ie. if a 3ms pulse lets 3grams of fuel past an injector, is the total amount of fuel used during each engine revolution 3grams * 4 or 3grams * 8?

I made some assumptions on the questions above and came up with this. I think it should allow you to determine instantaneous fuel mileage. Of course this could also be averaged over time to give you a long-term reading. I have no idea how to actually implement this though.

; consumption_gal_hr is the current fuel consumption in gallons per hour
; current_flowrate is the current rate of fuel flow in pounds per hour
; injector_flow_rate is the manufacturer rated flow in pounds per hour (@ 100% duty cycle?)
; current_duty_cycle is the current duty cycle that the injectors are operating at
; injector_pulsewidth_ms is the current injector pulsewidth in milliseconds
; max_duty_cycle_ms is the injector pulsewidth that equals 100% duty cycle (=injector_flow_rate?)
; 60000_ms_min = 60000 milliseconds in one minute
; current_rev_min is the current engine RPM

current_mpg = current_speed_mi_hr / consumption_gal_hr ; miles/gallon = (miles/hour)*(hours/gallon)

consumption_gal_hr = current_flowrate / 6.0 ; 6.0lbs/gallon
current_flowrate = (injector_flow_rate * current_duty_cycle )
current_duty_cycle = ( ( injector_pulsewidth_ms * 8 ) / max_duty_cycle_ms )
max_duty_cycle_ms = ( 60000_ms_min / current_rev_min ) )

Using this I came up with about 28mpg for one relatively average datapoint while crusing at highway speed. Seems a little high, but in the ballpark. Am I at least heading in the right direction?

-Bryan

First/Thrid Gen

You are asking the exact question I was gong to ask.

I will check your formula and the one I made last year that I used with excell and export to cvs in tuner pro. I came up with high 20 mile per gallon (imp) as well.

I would like to do a on dash display as well.

When I was doing the aldl definition file that I posted on the moates site I do remeber that the info for on dash was there but I did not know how to put the speed and the injector duty cycle and the rpm together to display a live reading.
Was only able to do this with the info exported and work the cells in excell to come up with a miles per gallon #.

On dash would be great as you could use RT and fine tune with out stopping and exporting.

Hope we can get some help, if not I will try to work this one threw with you.

I do find LSB MSB lingo over my helment at this point.

First/Thrid Gen

Here is my formala Yours may be right it is just easier explaining mine the going threw someone elses math

For 23.25 pound per hour injectors ( corrected 22 injectors due to pressure increase)

Miles per gallon = Speed / (RPM X Inj Pulse Width / 178.56)

The constant 178.56 comes from 600 X 8 X .2325 / 6.25

600 comes from 60000 - I can't remeber exactly were this comes from other then it has to do with taking the pulse width and making it a percent of flow against time for a 1 hour period so it can be calculated with the pound per hour.

8 is # of injectors

.2325 comes from pounds per hour

6.25 is pounds in a gallon us

So it becomes a simple matter of taking the above info (speed, rpm, injector pulse width) in cvs file and making a few extra cells with the correct excell math expresions and you have yourself miles per gallon at a sample rate of lets say 10 a secound.

I am just going by notes as I have lost all my cvs files from a recent computer upgrade.

This is handy but the quest for on live on dash is the new goal.

This may be over my head - more of a Mark Mansur Program Wizard type of goal.

First/Thrid Gen

Here is my formala Yours may be right it is just easier explaining mine the going threw someone elses math

For 23.25 pound per hour injectors ( corrected 22 injectors due to pressure increase)

Miles per gallon = Speed / (RPM X Inj Pulse Width / 178.56)

The constant 178.56 comes from 600 X 8 X .2325 / 6.25

600 comes from 60000 - I can't remeber exactly were this comes from other then it has to do with taking the pulse width and making it a percent of flow against time for a 1 hour period so it can be calculated with the pound per hour.

8 is # of injectors

.2325 comes from pounds per hour

6.25 is pounds in a gallon us

So it becomes a simple matter of taking the above info (speed, rpm, injector pulse width) in cvs file and making a few extra cells with the correct excell math expresions and you have yourself miles per gallon at a sample rate of lets say 10 a secound.

I am just going by notes as I have lost all my cvs files from a recent computer upgrade.

This is handy but the quest for on live on dash is the new goal.

This may be over my head - more of a Mark Mansur Program Wizard type of goal.