TwinTurbo.NET: Nissan 300ZX forum - Hard Closed Throttle Position Switch hardware testing
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Subject Hard Closed Throttle Position Switch hardware testing
     
Posted by earthpunk on May 06, 2017 at 10:58 PM
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Message ComradeZ:

No question, just sharing info...

Summary: The ECU does not normally use the Hard Closed Throttle Position Switch (HCTPS) hardware in the Throttle Position Sensor (TPS) unit to generate the Throttle Closed signal (see FSM page EF & EC-15). You can test your HCTPS using Conzult (with Ignition ON and engine not running) by disconnecting the TPS (grey and oval throttle position sensor) connector, of course you have to leave the black and rectangular HCTPS connector connected; the Throttle Closed signal will then be driven by the HCTPS hardware not the TPS position sensor hardware and rotating the sensor by hand or (if disassembled) pulling the contacts apart or pushing them together by finger should cause the Throttle Closed signal to change in Conzult.

More detail: I started troubleshooting my '93 TT smog failure due to rich idle (Z... I wish I was rich and idle instead of you...). Conzult showed me TPS position sensor was out of spec (WAS: 0.30V; SHOULD BE: 0.45+/-0.05V) at throttle closed and I noticed some incorrect Throttle Closed readings. I convinced myself that the throttles were closed, loosened the two TPS mounting screws (using a stubby "+" screwdriver), and tried to rotate the TPS unit to where the position voltage was in spec .AND. Throttle Closed was Closed but there was no such orientation (Throttle Closed was always Open when TPS read between 0.4V and 0.5V). Hoping that this was the reason for the rich idle, I disassembled (using a 1/8" drill bit and a drops of machining oil in a drill press to remove the 2 rivets in the TPS and a straight screwdriver to carefully pry off the black plastic cover thankfully without breaking it) my TPS and started cleaning and poking at the HCTPS hardware. After a lot of cleaning and poking I realized that there was no relationship between what I did to the HCTPS and what the ECU told Conzult about the Throttle Closed state. To confirm, I disconnected the HCTPS (rectangular and black, not oval and grey) connector on the TPS and confirmed that Conzult continued to get Throttle Closed signals from the ECU (and from the disconnected HCTPS by magic, apparently)! Belatedly, I read on FSM page EF & EC-15 that the "Soft Closed Throttle Position Switch" (I assume this is a software estimate of Throttle Closed signal based on the TPS position sensor data) is used normally and the HCTPS is only used when the "soft closed throttle position switch is malfunctioning". Thus, HCTPS failures won't normally have any effect on system behavior. Buggers; no closer to getting rich idle problem solved.

I set my TPS to spec (0.46V) and disconnected the TPS connector and waited for the TPS voltage in Conzult to max out (5V) and for the Throttle Closed signal to change to 1. I then reconnected the TPS connector and the TPS voltage went back to 0.46V and Throttle Closed stayed 1 and worked normally after that. I found this procedure at https://z32.wikispaces.com/Throttle+Position+Sensor?%20responseToken=0169bd35f0cc39eb5fdb365cb3a6a5013&responseToken=09109aef9f94d29847a51e79530795dd

I noted that the TPS runs on 5V and the HCTPS runs on 12V power and Throttle Closed 0 is Throttle Open and 1 is Throttle Closed.

DosZvedanya,

     
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