747 meet 730, 730 meet 165

[Clive Apps Techno-Logicals 416 510 0020]

> 
> I think  the sensors that get gnd and +5v such as the map and tps (not
> the [heated] O2) can be shared.  I don't think they rely on a resistor
> divider arrangement like the coolant temp sensor.  The map on my '92 GM
> truck even appears to have an internal amplifier/buffer (can't measure
> resistance, but give it gnd and +5v and a voltage that changes with
> vacuum comes out [no pullup needed]).
> 
> Using an external pullup on the coolant sensor followed by an op amp may
> or may not work.  Others on the list indicated that some ECMs switch in
> different pullup value depending on the temperature (improves ECMs
> measurement resolution over particular ranges).  If you're just using
> potentiometer to simulate the coolant sensor, adjust the pot for the same
> voltage in the dual ECM case as in the single and they should indicate the
> same temperature.  The only time the pot may be a problem is when your
> near the range where the ECMs want to switch the pullup value -- anyone
> know about what temperature this happens?


an op amp could also be used as  buffering device with unity gain to
take care of the inputs that are current based

Clive