Dan,

The "higher input range" is really a red herring - there is no such thing at least in terms of voltage. The ECU can't see higher values because even if the input went higher electrically, the computer can't go any higher numerically. For example, if they're using an 8-bit A-to-D (which is common), it will output numbers from 0 to 255 corresponding to input voltages from 0 to 5 volts. 255 is the largest number you can store in 8 bits, so no matter what happens the computer cannot see a higher value. In the real world, if you increase the voltage up to a point the computer will just see the maximum A-D value. Increase it more and you'll damage the circuitry!

What happens is that higher airflow capacity is dealt with elsewhere in the system. For example, the airflow ECU inputs on a naturally aspirated Saab and a Buick Grand National both go 0 to 5 volts over thier respective airflow ranges. But 5 volts on the Buick represents a much higher airflow than on the Saab.

To go along with higher airflow, you need more fuel, but that doesn't by definition mean you need a larger input to the ECU. You can change the fuel on the *output* side too, simply by installing higher-flow fuel injectors, or raising the fuel pressure. Or, change it inside the ECU by changing the software to pulse the injectors for longer. Manufacturers balance these and other parameters to ensure that enough fuel is available at high load, while trying to maintain fine enough control that the engine will run well at light load.

Eric Law

posted by 63.173.23...

• KevinK and others: AMM question, Dan Schleifer, Wed, 6 Nov 2002 10:15:32
  • some info, comments Ragnar?, Kevin K , Wed, 6 Nov 2002 14:41:25
    • Re: some info, comments Ragnar?, Ragnar, Fri, 8 Nov 2002 06:03:33
  • Re: AMM answer, Ragnar, Wed, 6 Nov 2002 11:06:17
    • response, Dan Schleifer, Wed, 6 Nov 2002 11:20:20
      • Limitations, Eric Law, Wed, 6 Nov 2002 12:25:50
        • Re: Limitations - question about Volvos, Dan Schleifer, Wed, 6 Nov 2002 13:35:30
          • Re: Limitations - question about Volvos, Eric Law, Wed, 6 Nov 2002 15:36:36 <-- Viewing This Message
          • Volvo AMM has a larger ID., RSS, Wed, 6 Nov 2002 14:52:40

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