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12.17 - Fuel Fail 17 : TPS out of range low ( Brett Gadzinsky,  )

Conditions for flagging : signal to ecu under 250 millivolts for 64 milliseconds.

The throttle position sensor is used by the ecu for :

- Idle speed control,
- Ignition idle strategy selection,
- Overrun fuel cutoff,
- Idle fuel trim (1990 to 1992)
- Main fuel metering strategy,
- Main ignition strategy,
- Acceleration strategy,
- Deceleration leaning,
- Full load enrichment.

Default settings while FF17 is flagged is 1.5 volts, and all throttle position sensor functions do not operate.

Possible faults :

- High resistance at throttle position sensor or ECM,
- Short or open circuit in wire harness between tps and ecu,
- Loose or incorrectly adjusted throttle position sensor,
- Defective throttle position sensor (worn).

On the 1990 to 1992 year cars, the tps has two separate sensors in one housing, one does the engine, the other does the transmission. After 1992, one sensor talks to both the engine and trans. On the early cars, to about 1993, the sensor is under the throttle and is turned by the throttle shaft.

Various year cars had different idle voltage settings :

87-88 .24 - .40
89-90 .31 - .36
90 and up .57 - .62

Full throttle should read about 4.5 volts.

Be careful to prevent anything getting in the tps while cleaning the throttle out...don't spray any cleaners in the throttle or the gunk will wash into the sensor.


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