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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 Body Cleanliness
•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.
Throttle Position Sensor
Rotational Angle Signal Voltage
0 Under Travel 0.000
13 Closed Throttle 0.901
20 - 1.440
84 Full Throttle 4.538
90 Over Travel 4.538
Values were calculated for VREF = 5.0 volts.
These values may vary 3 percent due to sensor
and VREF variations.
Additional INFO: These are other things that can be found about
Ford Fuel Injection at fordfuelinjection.com.