Date: Sun, 27 Jul 2003 16:10:51 -0400
From: Malcolm William Mason <MWM1nopsamedu>
Subject: Re: Gas economy

I have "checked" the EDU values by using the trip odometer and gallons fromFull to Full. The values I get are comparable. The gallons ar4e checked reularly by the jurisdiction's (state or province) Weights and measures departments and mileages on major highways in the U.S. and Canada are posted in 0.1 mile or 100 metre increments by the Departments of Highways and are very accurate. True, the fuel injectors wear with time but this is compensated for by the fuel management system. The data are empiric and "jibe" with the EDU. My best guess is that it is quite accurate. Malcolm On Fri, 25 Jul 2003 15:10:01 GMT, hohnopsamlid.invalid (Goran Larsson) wrote: >In article <>, >Andy Hookins <> wrote: >> "Goran Larsson" <hohnopsamlid.invalid> wrote in message >> > >> > The EDU measures two signals for its fuel consumtion numbers. One signal >> > is the distance driven, i.e. the same signal that is used by the >> > speedometer, odometer, and some other functions in the EDU. The other > >> I defer to your knowledge over my speculation >> (i.e. my previous post elsewhere in this thread). I just >> assumed that the EDU is a dumb display driver, but you >> say it has signal acquisition and computational abilities, >> is that right? > >The EDU that I am familliar with is the one used on the 9000. That EDU >had a wire directly wired to one of the injectors (for the injector open >time) and one wire to the speedometer (for the speed signal). All >numbers shown on the EDU was calculated inside the EDU itself. > >> > signal is the time the injection valves are open. As the volume that >> > passes through the injection valves over a certain time is known it is >> > easy for the EDU to calculate the fuel volume used. Later Saabs with > >> This description implies to me that there is another method >> of determining fuel used - maybe the fuel tank sender, to >> compensate for diffeences in fuel injector characteristics. > >The injector characteristics must be known. How else is the engine >management computer supposed to determine the correct time to keep >the injector open? > >The fuel pressure over the injectors is determined by the fuel >pressure regulator. It should be constant and fixed. Knowing >the characteristics of the injectors and the time they are open >allows the EDU to calculate the fuel consumption. The engine >management computer can not read the fuel pressure, so if it is >wrong then both the amount of fuel injected, and the values shown >on the EDU, will be wrong. > >> Is that what you are saying or am I just reading more into >> this than I should? > >I can't answer that as I don't know what you are reading that >shouldn't be read.

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