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throttle possition test

EFI Tuning Fundamentals

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Is their a way to test the throttle pin out, if its unknown? with a multi meter?

For a traditional pot, the resistance will be fixed across two pins, and vary as the pot is moved across any other combination. So, using an ohmmeter first find the two pins that have the highest resistance (typical 4k - 10k ohms), then with the ohmmeter still connected, move the sensor. If the value didn't change, then you have the VRef and 0V pins identified (if it does move, there might be another combination with the same high resistance -- try that). The other pin should be the signal. Usually, the resistance between the signal and 0V will be the lowest resistance, so the voltage will increase as the throttle is opened.

okay doky,

0 volts means negative?

0V (Zero Volt) is usually the signal ground, or the ground for the Reference Voltage (VRef -- typically 5 volts).

As David said, for a 3 pin TPS, normally there is one pin that is 5V input, a 0V ground, and a pin that has a variable resistance, relative to each of the other pins, as the throttle is moved.

If the resistance across two pins is constant with the throttle being moved, they'll be the 5V and 0V (ground/earth) pins. You can check by leaving one connected and checking the other pin as the throttle is moved, then try the other, one should increase and the other reduce resistance as the throttle is moved.

The actual problem may be how the ECU interprets the changing voltages - it compares the variable voltage to the fixed (nominal) 5V and 0V to give the position of the throttle blade - as some will have closed low and open high, and others the other way round.

You may find this diagram useful - ""