Throttle Position Sensor (TPS)
The throttle position sensor is mounted on the end of the throttle body and tells the computer how far open or closed the throttle is. The TPS is pretty easy to understand how it work's, it is a potentiometer just like your dimmer switch in the dash. Voltage is fed to the TPS by the signal return circuit. As the throttle is opened the TPS directs more voltage to the EEC and less down the voltage reference circuit. All of the following items will affect the TPS:
•Throttle Cable
•Throttle Body Cleanliness
•Vacuum leaks
•Air Filter
•Air Filter to Throttle Body Duct
•Engines general condition
•Harness and wire general condition
The TPS sensor has a great deal of influence on the fuel ratios and timing curves, because the TPS is a user interface sensor. The TPS is the closest thing you have to a phone call into EEC. EEC listens to your every command from the TPS. There is a TPS ratchet algorithm which continuously seeks the minimum throttle angle corresponding to a CLOSED THROTTLE position. This alleviates the necessity to set the throttle position sensor at an absolute position and compensates for system changes and differences between vehicles.
•Closed Throttle can be anywhere between 0.6-1.0 volts
•Part Throttle is triggered @ 0.04 volts above Closed Throttle
•Full Throttle is triggered @ 2.71 volts above Closed Throttle
Before testing the TPS or any other EFI component perform a self-test, trouble codes received during test can be used as a diagnostic tool along with other indicators. To test the TPS sensor you will need a volt meter. You need to back probe the harness while reading the voltage between the TPS and SIG RTN pins. The exact voltage you get at any one point is not of major concern; instead you need to watch for a smooth increase in voltage as the throttle is moved. A TPS that does not give a steady increase in voltage as the throttle is moved is faulty and needs to be replaced. Also check for mechanical problems associated with the throttle. Throttle linkage and cable can bind up, keeping the throttle from opening correctly. Some times the idle stop screw has been adjusted, this adjusts the base idle and moves where the TPS closed voltage. The TPS should not need adjustment, but once the idle screw has been tampered with, the TPS should be adjusted to match. If the idle is low and the TPS is high lots of problems will appear. If you need to grossly modify the TPS mounting holes to adjust Closed Throttle between 0.6-1.0 volts, you should recheck the idle stop screw first.
| Values were calculated for VREF = 5.0 volts. These values may vary 3 percent due to sensor and VREF variations. |
||