Testing TPS on 2.9
bronconut
11-06-2005, 11:52 AM
I think my TPS may be bad on my 88 2.9. How can I test it? What wires do I connect my volt meter to?
OP
OP
stuzman
11-06-2005, 02:13 PM
I think my TPS may be bad on my 88 2.9. How can I test it? What wires do I connect my volt meter to?
OP
Most problems with the TPS will lie within the bottom third of the sensor since that's where it usually stays while we're driving. Usually, an open will occur at some spot in this area which can give symptons of hesistation or rough idle. There are three wires to the sensor:
One wire is 5VDC (reference voltage) from the PCM, second wire is the signal ground (also from the PCM) and the third wire is for the signal input (the wiper of the pot, i.e. center wire on sensor) sent back to the PCM to measure the position of the sensor.
You can check the voltage or you can check the resistance. DON'T use an analog meter to measure voltage (use only a digital meter) since its input impedance is around 20K ohms (much to low to be working around computers). You can use an analog meter if you only want to measure the resistance.
Assuming that you're going to measure voltage...hookup the meter leads to the signal ground and to the center wire and set the meter to read DC. Turn the ignition on (engine off is fine) and you should measure a low voltage probably around .4-.5VDC at idle. Hopefully, your meter has the analog bar graph which gives a much faster update than the numerical values. It's possible you could miss an open spot on the sensor if you monitor only the numerical values and operate the sensor too quickly. The voltage should vary smoothly from idle to approximately 5VDC as the throttle is varied. If the voltage fluctuates or drops out, then you have a bad spot on the sensor. You can do the same thing with a resistance check of the sensor, but disconnect the connector from the sensor with ignition off and engine not running.
If you have an analog meter, then this will give you a much better indication than a digital meter unless it has an analog graph. Again, DON'T measure the voltage with an analog meter, only the resistance with the connector unplugged. The needle should vary smoothly as the throttle is varied by hand. If you see a fluctuation in the needle, then it's a bad sensor.
As far as which wires to connect...the center wire will be connected to the positive lead of the meter. For the signal ground, just pick one of the other two...if the voltage comes back near 5VDC at idle, then it's the other wire. You'll know the signal wire is correct when the voltage will read low (.4-.5V) when at idle.
Personally, I like to check the voltage since you can monitor the voltage from the PCM at the same time. If your meter has a Min/Max feature you will know when your voltage falls below a minimum threshold thereby detecting bad spots on the potentiometer.
OP
Most problems with the TPS will lie within the bottom third of the sensor since that's where it usually stays while we're driving. Usually, an open will occur at some spot in this area which can give symptons of hesistation or rough idle. There are three wires to the sensor:
One wire is 5VDC (reference voltage) from the PCM, second wire is the signal ground (also from the PCM) and the third wire is for the signal input (the wiper of the pot, i.e. center wire on sensor) sent back to the PCM to measure the position of the sensor.
You can check the voltage or you can check the resistance. DON'T use an analog meter to measure voltage (use only a digital meter) since its input impedance is around 20K ohms (much to low to be working around computers). You can use an analog meter if you only want to measure the resistance.
Assuming that you're going to measure voltage...hookup the meter leads to the signal ground and to the center wire and set the meter to read DC. Turn the ignition on (engine off is fine) and you should measure a low voltage probably around .4-.5VDC at idle. Hopefully, your meter has the analog bar graph which gives a much faster update than the numerical values. It's possible you could miss an open spot on the sensor if you monitor only the numerical values and operate the sensor too quickly. The voltage should vary smoothly from idle to approximately 5VDC as the throttle is varied. If the voltage fluctuates or drops out, then you have a bad spot on the sensor. You can do the same thing with a resistance check of the sensor, but disconnect the connector from the sensor with ignition off and engine not running.
If you have an analog meter, then this will give you a much better indication than a digital meter unless it has an analog graph. Again, DON'T measure the voltage with an analog meter, only the resistance with the connector unplugged. The needle should vary smoothly as the throttle is varied by hand. If you see a fluctuation in the needle, then it's a bad sensor.
As far as which wires to connect...the center wire will be connected to the positive lead of the meter. For the signal ground, just pick one of the other two...if the voltage comes back near 5VDC at idle, then it's the other wire. You'll know the signal wire is correct when the voltage will read low (.4-.5V) when at idle.
Personally, I like to check the voltage since you can monitor the voltage from the PCM at the same time. If your meter has a Min/Max feature you will know when your voltage falls below a minimum threshold thereby detecting bad spots on the potentiometer.
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