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rmccomiskie
EcoModding Lurker

Join Date: Aug 2008
Location: Massachusetts USA
Posts: 84

Ziggy - '95 Audi S6 Sedan

Manfred - '97 Audi A6 Quattro Sedan
90 day: 20.61 mpg (US)

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Quote:
 Originally Posted by Funny 1 microsecond, or µsec, = 1.0 × 10-6 seconds. Simply 1 µsec = 0.000001 seconds. This is territory I haven't entered yet, but the MPGuino guys will answer this better than I can. I believe that Injector pulses are 2 pulses per rotation, open and close, and this is part of the rpm, so 6000 pulses would be 3000 Rpm, then a certain number of pulses = 1 gallon of fuel dispensed. I hope I am right, but please disregard If I am later proven incorrect. I know I am right on the conversion though .
Almost correct. A single injector (port injector type, not TBI)) will be pulsed open for some number of microseconds once in two revolutions of the engine. The MPGuino is tracking the moment in time when the leading of the pulse occurs and then when the trailing edge occurs. Time, in this case, is measured in microseconds, i.e. millionths of a second. The time of the leading edge is subtracted from the time of the trailing edge to get the elapsed time of the pulse. All of the elapsed times are added together to get the total amount of time that the injector is open. After you've calibrated the number of microseconds it takes to spray one gallon, that number is divided into the total time to get the number of gallons sprayed.

For example, if the total open time is 1,455,788,104uS and you have calibrated the fuel usage as 200,500,000uS/gal:

1,455,788,104 / 200,500,000 = 7.26 gallons

So, there's nothing magic about the total microseconds. It's just the total elapsed time that was needed to spray 7.26 gallons. Once you've calibrated your fuel usage, it should consistently indicate the gallons used.