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I have a little digital screen in my dash that re-evaluates my average fuel consumption (L/100km) every thirty seconds. How can I modify this to increase the reporting frequency? Preferably, at least once every second (or more) would be ideal. Thanks in advance.

It's a 2005 Holden VZ Commodore SS. You probably know it as a Chevrolet Lumina or Chevrolet Omega. It might also be known by other names in different parts of the world, i.e. Vauxhall & Opel.
It looks like the image attached below.

See the glowing green LCD behind the steering wheel, with the odometer readout? Thats also where the fuel consumption displays. You just have to select it with the buttons to the left. Interestingly enough, you can see the Monaro (in the final image) actually has a seperate digital fuel consumption readout on the fuel gauge itself.
VZ SS Exterior VZ SS Interior

VZ Berlina Interior VZ Monaro Interior

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    This probably requires patching the car's software somehow. There might be patches like this available for some cars, but it would be specific to your make, model and year (maybe also country, trim level, etc), so please state what they are. Also note that even if this is possible, it might negatively affect your warranty. And a higher report frequency might give you reports that are much less accurate.
    – Nate Eldredge
    Oct 26, 2015 at 23:49
  • Along the lines of what @NateEldredge said, moving your report time up to 30x normal may have an adverse affect on the hardware ... it may overtax it to the detriment of other things, like how it runs the vehicle (if the PCM does all the calculations).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 27, 2015 at 0:43
  • @NateEldredge I updated the post as per your request. Warranty is long gone by now though, FYI.
    – voices
    Oct 27, 2015 at 21:01

2 Answers 2

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For what it's worth, there is a way to access the instantaneous fuel flow rate inside the secret menu on this model. I know this is not exactly what you're after but this parameter has a very fast refresh rate, and to obtain the l/100 km reading it you simply have to divide the value by vehicle speed and adjust for units if needed.

With the key in the "off" position, keep the "Mode" and "Set" buttons pressed and then turn the car on.

This will give you access to some neat metrics including battery voltage, fuel flow rate, digital tachometer and vehicle speed.

You can cycle through the options using the "Mode" button.

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  • Seriously? I will have to try this out and let you know how it goes.
    – voices
    Dec 20, 2015 at 5:02
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It is not possible . Firstly lets see how the system works : 1. The speed/distance sensor measures the distance you have travelled in 30 seconds . 2. The ecu calculates the amount of fuel that has been sprayed into each cylinder during that 30 second period. 3. Simple math distance ÷fuel consumed = mileage

If it was timed to one second the percentage error in the calculation would be greater . In typical city speeds if you are doing 50 kmph in a second you would have travelled approx 14 meters i.e 0.014km and fuel consumed would be approx 9 to 14 ml i.e 0.009L/0.014 L. So percentage error would be huge . 3 places behind decimal will give you a very large error. Can be upto 50 % Spreading it out over 30 seconds eliminates majority if the error ! And for mileage calculation you need an average calculation .

And if you think about it carefully , if you were to make a mileage meter that can give a reading every second , it would be very similar to a reverse working tachometer. Higher the needle goes lower the mileage you get .

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  • I've seen this kind of thing implemented many times before. I drove a VZ Calais, for instance, that had a real-time digital fuel economy readout. You're right though; it was about as dynamic and responsive as the tachometer.
    – voices
    Oct 27, 2015 at 20:56
  • Yes and that was the real problem. If you dont take your readings for a longer period of time the digits are always wrong.
    – Arka Patra
    Oct 27, 2015 at 20:58
  • It seemed quite accurate. Regardless, it is suitable for what I have in mind.
    – voices
    Oct 27, 2015 at 21:07

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