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Aaron Cake
Administrator
Canada
6718 Posts |
 Posted - Sep 10 2004 : 08:47:46 AM
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From pulsewidth you can easily get duty cycle. So, to sum up, you need:
1. Measure pulsewidth/duty cycle of injectors
2. Measure speed and distance covered
You need to know:
1. Your fuel pressure. This can change (some cars reduce voltage to the fuel pump at idle, thus reducing pressure) so confirm that your car uses a single fuel pressure.
2. The size of your injectors. Normally in CC or LB/Hour. This tells you the flow rate if the injector is wide open. This changes with fuel pressure, which is why pressure is important. With pressure and your injector size, you can calculate fuel flow if the injector is wide open.
3. Injector duty cycle/pulsewidth. This tells you how long the injector is open. You can now calculate fuel injected per event, then use your distance and speed to determine your average MPG.
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n/a
DELETED (Inactive)
4 Posts |
Posted - Sep 27 2004 : 9:23:49 PM
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Most cars change the fuel pressure (line pressure) with a vacuum pod on the fuel pressure regulator that is connected to the intake manifold. When the vacuum drops down the fuel pressure (line pressure) goes up, this is to compensate for the change in manifold pressure (which effects the fuel flow rate). Theoretically this keeps the fuel flow through the injector the same whether the fuel pressure is 45psi and manifold vacuum is 20" or if the fuel pressure is 52psi and manifold vacuum is 0" and everywhere in between. I made up the numbers but they are actually pretty close to what a typical car would be.
BTW most BMW's come with a MPG gauge in the car, I think for the most part it just uses Pulse width and distance (or it could be speed) for the calculation.
Ramon
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GMP
Apprentece
15 Posts |
Posted - Apr 02 2005 : 12:03:38 PM
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Looks like I am entering this discussion in the end zone, but I wanted to add that if the system is computer controller and has an ALDL connector, you might be able to get the info out to a laptop from there. I have found an excellent site regarding this here:
http://www.techedge.com.au/vehicle/aldl8192/8192hw.htm
It is a simple RS232 interface to read several parameters from the on-board computer.
-George |
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Kevinlekiller
Member
Bangladesh
45 Posts |
Posted - Apr 07 2005 : 12:33:42 PM
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Hi YS, why dont you get an OBD-II connector and some software and hook it up to your laptop (if you have one). OBD-II is on all american cars that where made after 1995 or 96. Im not 100% sure if it tells you how much gallons of gas your burning per mile. Heres a site to start you off: http://www.obdii.com/
Bab Himself |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Apr 08 2005 : 09:56:36 AM
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OBD-II is a requirement for all cars sold in North America since 1996.
Mileage is not a standard function of OBD-II. It depends on the vehicle, and the software. The software generally "guesses" based on other parameters.
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Fuel economy
