I've always wondered what information the EDU uses to calculate the MPG. Obviously, the ECU knows precicely how much fuel is supposed to be delivered at any given moment. (Note: EDU and ECU are two different things)

When you reset the MPG indicator using the little "R" button (on the highway for instance) the readout stays blank for 1/8 mile or so, then gives a reading that initially fluctuates very quickly, and then settles down as more data gets averaged in.

Here's my guess as to how your MPG indication increased (a lovely little esoteric theory, this):

I would assume that since the fuel is at relatively constant pressure in the rail, then the injectors change the quantity of fuel by ajusting the duration of the nozzle opening. Your new sofware knows that the larger injectors need shorter nozzle opening times for the same quantity of fuel.

The question is, does the EDU know this? The software that controls the fuel is entirely separate from the EDU. Perhaps the EDU reads and aggregates sets of data from the ECU about the duration of nozzle openings, correlates that to a quantity of fuel in gallons. So therefore, if it is now consistently recieving data that suggest shorter duration nozzle openings, then it mistakenly calculates that the car is using less fuel per mile.

-Kyle
'91 9000T

posted by 64.65.195...

• Anomaly alert!........., zeke, Fri, 17 May 2002 15:08:37
  • I have an anomaly alert, too, Bob Davis, Sat, 18 May 2002 13:38:31
    • Major misunderstanding........., zeke, Sat, 18 May 2002 18:19:44
      • A misunderstanding, but not major, Bob Davis, Sat, 18 May 2002 20:43:04
  • me too, with SQR chips., John Rose, Fri, 17 May 2002 17:02:02
    • Wait a minute............., zeke, Fri, 17 May 2002 17:11:03
      • Yes, it's a '91.., John Rose, Sat, 18 May 2002 15:33:17
  • Perhaps the EDU is wrong >>>, Kyle, Fri, 17 May 2002 16:11:59 <-- Viewing This Message
  • Re: Anomaly alert!........., 97SAAB, Fri, 17 May 2002 15:31:37
    • Of course,........., z eke, Fri, 17 May 2002 16:36:29
    • 97SAAB was a bit more concise than I! :) (n/m), Kyle, Fri, 17 May 2002 16:16:29

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