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Old 09-18-2002, 11:30 AM
sbourg sbourg is offline
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
I reiterate that I am simply approaching your posts by starting at electronic basics. I find them confusing because you are not using termnology consistent with what I am familiar. So here goes:

'Perhaps I should have been clearer: Potentiometer 14-18 resistance 3200 ( 3240 some listings) to 4800 ( 4840 some listings) Is 1% over range limit unacceptable?'

Problem #1 - I don't know what you are referring to by 'listings'. Are you getting your information from various sources? 1% in a pot is excellent.

'I get a different reading at the connector than I do at the pot itself, I suspect due to this sharing of a lead with another variable resistor. At this point, confusion takes over, for the test of the baro sensor is an amperage one instead of a resistance check. I manually changed the pressure and saw changes in resistance through the baro sensor, with no dead spots'

If your primary concern is proper functionality of a potentiometer, it should be measured disconnected from the rest of the circuit, and certainly with no external voltage or current source applied. Else, any resistance readings will be meaningless.

Once you have determined that the resistance readings are correct at the extremities, and that there is no sign of intermittant operation at any point in the normal range of its travel, the pot has been tested adequately.

'My guess is that this system uses these variable resistance elements, such as the O2 sensor, coolant temp, air plate deflection potentiometer, and barometric pressure sensor as a series that starts with a known voltage and amperage, passes it through the variable resistors to achieve either a counterbalance to the nominal output current, or it becomes the output current.'

The computer can sample an input one of two ways. It can supply a known current OR a known voltage. It cannot simultaneously do both. Ohm's Law A=V/R shows this. If the ECU supplies a known reference voltage, it will sample the current flow through the circuit by monitoring the resulting voltage drop across an internal calibrated resistance. If is sources a calibrated current, it simply monitors the voltage across the sensor resistances. Knowing which mode of operation the ECU is in will make more sense of your measurements. If the manual says it is sourcing a current, you need to measure voltage drops. If it asks you to measure currents, it is sourcing a voltage reference.

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