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honda ect/iat/map/fuel level sensor data
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Hello. Im setting up a EG civic with a b20vtec with race capture pro. Ive found resistance data for them, but cant find voltage output data. Can anyone help me out with this? Also when i set up RPM, at 4 pulse per revolution the RPM was about half. Setting it at 2 pulse per revolution has the RPM matching what the gauges are showing. Im not sure if this is correct or not.


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Junction Auto Sport
ChumpCar Canada
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ECT pdf


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Junction Auto Sport
ChumpCar Canada
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IAT pdf


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Junction Auto Sport
ChumpCar Canada
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LDForget wrote:
IAT pdf


found a website with IAT voltage maps :

http://twiki.pgmfi.org/bin/view.pl/Library/IntakeAirTemperatureSensor


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Junction Auto Sport
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Hi Lee,

So you're tapping into existing sensors - we recently wrote a wiki article about that:
https://wiki.autosportlabs.com/RaceCapturePro2_hardware_guide#Tapping_into_existing_Sensors

This is actually a rather advanced topic, but possible with RCP.

So, the OEM thermistor sensors have variable resistance based on temperature and this forms a voltage divider so the ECU (and RCP) can see a variable voltage.

To understand voltage dividers, think of it as splitting the voltage between 0v and the reference from the ECU (typically 5v). As the resistance varies on the sensor, so does the voltage going to the ECU.

As described in the wiki, you can directly measure the voltage going to the ECU as it sweeps across the temperature range. Note the voltage sensed by the ECU based on the temperature. This is the brute force method.

The alternate way is to figure out the voltage reference (likely 5v) by disconnecting the sensor and measuring the voltage coming from the ECU. With the sensor unplugged, this breaks the voltage divider and you can measure the voltage reference.

Once you know the voltage reference, then you can figure out the ECUs internal pullup resistor by plugging the known values into the voltage divider calculator: Here's a handy one http://www.raltron.com/cust/tools/voltage_divider.asp

* the measured voltage with sensor disconnected into the volts field (the voltage reference)
* the resistance of the sensor at the current temperature into R2 (sensor disconnected, or use the data sheet)
* and the measured output voltage into the output voltage field (with the sensor connected)

Once you hit calculate you'll get the R1 resistance, which is the ECUs internal pullup.

Now, you can extrapolate this into additional points across the temperature range. Using the calculator, use the voltage reference, the R1 resistance, and the sensor's resistance in the datasheet for the desired temperature.

Recommended is to do 5 points from low to high; RCP will interpolate the sensor readings between points.

That was a lot, I know - but as before, it's an advanced topic, but possible. If all fails, you can brute force it by running the sensor through a range and directly measure the voltage going to the ECU.


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Brent Picasso
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