Fuel consumption data

[9c1vs]

Hi,

I was just wondering if anyone knows exactly what is the information supplied to the trip computer dash for fuel consumption? I know it has something to do with pulse width, but what are the values sent to the dash?

The reason I ask is I actually have a haltech platinum sport gm, which has the fuel consumption output enabled, but it is way off. The bloke said the haltech spits out a value something like 10% of the pulse width or something, but I did not ask for details. My fuel consuption reads less than 1/2 what it should be.

Just thought if someone knew exactly what it was that the delco sends to the trip computer/dash and didnt mind telling me, I will pass that info onto Haltech so they can correct their program and I can get correct fuel use data again

But if your not comfortable with sharing this type of info as I will be sharing it with another manufacture I understand.

Cheers.

[Holden202T]

this might be the stuff you need to look at (this is whats in a standard computer)

trip computer.jpg

[9c1vs]

So the actual data that is sent from the computer is variable and adjusted using tuner pro?

[The1]

on VT up it would be as the cluster is on the data bus, earlier models arn't on the data bus, you can adjust the cal in the hidden mode, this is for lvl 3 clusters.

[VL400]

Yep, can change pretty much everything with TP and a factory ECU/PCM

The L/hr figure is not used for the in vehicle trip computer, its used for the L/100 trip comp display while logging.

The amount of fuel for 1/256 duration is the PWM signal sent to the in vehicle trip computer. The signal is an 8 bit PWM, so has 256 steps. In the screen shot above, that would mean each step corresponds to 1.54msec of fuel delivered. It is calculated every 125ms. So if 20ms of fuel was delivered in the previous 125ms the output would be 20ms/1.54=16 so 16/255 or a 6.3% duty cycle signal

[The1]

arh cool, been wondering that, thought it was just for the databus, can tune the logged display now

[VL400]

On VT and later there are two figures sent to the dash, the above was for VS and earlier.

So for VT on, there is Fuel Used and Fuel Flow that get sent over the ALDL bus...
- Fuel Used is 1ml/bit and is fuel PWs summed over 100ms so the dash can use it for fuel consumption. It then uses a scalar that accounts for inj flow rate.
- Fuel flow is L/hr and is 0.01L/bit. It is constantly being updated, the dash gets the latest reading. Basically as the PCM knows the airflow and target AFR it calcs the fuel flow using a single scalar to simplify things.

[9c1vs]

ok, I think I have my head around it. Basically in TP, that slide bar which adjusts the ms per 1/256 basically allows you to adjust the percentage of duty cycle that is given to the trip computer in order to calculate L/100km. I am guessing this is so that tuners can adjust for larger injectors, as the % of duty cycle output will need to change for bigger injectors for the trip computer to get it right.

What would a standard value for standard 195cc injectors be? I am guessing a value that equates to more than 10% duty cycle, as that's what the haltech sends and it is way to low a value for correct fuel consumption to show on the trip computer.

[Holden202T]

that information above is from standard VR V6 commodore i think it was.

[9c1vs]

oh ok cool cheers, does anyone have one for a v8?