Low TPS input voltage

I have been working on a rough idle problem on my 89 4.0. WHile attempting to adjust the TPS, I noticed my input voltage was 3.84. Everything I read says it should be 5V. Do I have enough voltage for it to work correctly? If not, is an ECU change the only way to fix it?

Sounds like you have the input and output confused, typical input is 4.6-4.8 volts. Having said that, check it to battery (chassis) ground instead of using the TPS sensor ground. Check the TPS ground for ohms (resistance). Connectors are a good place to look, when I first got my 88 there was a rather large voltage difference at the TPS connector, testing one side of the connector to ground then the other side of the connector to ground. At some time or other somebody had sprayed it with something (WD 40 maybe) that coated the pins and added resistance.
Checking the voltages at the connector is often iffy, I run the TPS wire over the top of the airbox to TB rubber and put a couple of exacto kniofe cuts through the insulation (lengthwise). You can reseal with a dab of silicon, I leave mine open (for the next time) and just cover with a piece of tape.

My TPS wires have been this way for around 5 years or so, makes testing easy, never caused any issues I've noticed (rubs the hood insulation a little).

8Mud said:

Sounds like you have the input and output confused, typical input is 4.6-4.8 volts. Having said that, check it to battery (chassis) ground instead of using the TPS sensor ground. Check the TPS ground for ohms (resistance). Connectors are a good place to look, when I first got my 88 there was a rather large voltage difference at the TPS connector, testing one side of the connector to ground then the other side of the connector to ground. At some time or other somebody had sprayed it with something (WD 40 maybe) that coated the pins and added resistance.
Checking the voltages at the connector is often iffy, I run the TPS wire over the top of the airbox to TB rubber and put a couple of exacto kniofe cuts through the insulation (lengthwise). You can reseal with a dab of silicon, I leave mine open (for the next time) and just cover with a piece of tape.

My TPS wires have been this way for around 5 years or so, makes testing easy, never caused any issues I've noticed (rubs the hood insulation a little).

Click to expand...

I will have to double check it. I was getting output in the .18-.20 range.

That 5 volt signal is used by other sensors (I guess as it really doesn't make much sense to have multiple drivers). The "C" pin at the MAP is also 5 volts in, worth a quick voltage test to chassis ground. Pin "B" should also read 5 volts, with the key on, after the motor is running it should drop off to around 1-1.5 (or maybe a little higher) volts, at the "B".
Unplug your sync sensor and recheck the voltage, just in case the sync sensor is sucking down the 5 volt.
My bet would be the sensor ground circuit, then maybe a corroded connector in the 5 volt in circuit.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm