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  1. #1
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    Question throttle position sensor failure symptoms

    just read the 'getting crazy with ignition timing' thread and it made me curious if you brainiacs would help me identify symptoms and problems one is likely to encounter when they have a faulty TPS. i'd imagine the following;
    - erratic idle (below ~800 revs)
    - stalling when coming off the throttle
    - any more symptoms..?

  2. #2
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    Friend had same problems with the tps unplugged tps and ran better so he put new tps on now and sorted

  3. #3
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    Arrow specific symptoms

    @buckets: do you know what symptoms your friend suffered with the buggered TPS..? that's what this thread is about..
    all input appreciated so don't feel shot down..

  4. #4
    Administrator Texx's Avatar
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    First you need to understand what the TPS does and how the ECU interprets the position of the TPS.

    The TPS is basically a switch. It has:

    3 wire terminals
    • IDL (Idle switch)
    • E2 (Sensor ground)
    • PSW (Power switch)

    2 switch contacts
    • IDL>E2
    • PSW>E2

    3 positions
    • IDL>E2
    • OFF
    • PSW>E2

    So the TPS at any given time will either connect the IDL and E2 terminals or the PSW and E2 terminals of the ECU or won't connect either.

    TPS Position 1: IDL>E2

    When the throttle plate is closed or less than 1.5 open the TPS connects the IDL terminal to the E2 terminal of the ECU. The ECU constantly monitors the IDL signal voltage and when it drops from 5v to 0v (because it's been grounded by E2) it knows the throttle plate is in it's closed position.

    When engine coolant temperature is above 80C, engine speed is below 2000rpm and the TPS at position 1 the ECU: goes into a closed loop operation using the feedback signal from the 02 sensor to adjust fuel injection, advances and retards the ignition timing and also operates the IACV to maintain the correct engine idle speed. To correctly set the engine idle speed and initial ignition timing angle the idle correction function of the ECU needs to be disabled, this is done by shorting diagnostic terminals TE1 and E1 and will only work with the TPS at position 1.

    When engine coolant temperature is above 80C, engine speed is above 2000rpm and the TPS at position 1 the ECU determines that the engine is on overrun and deceleration is occurring. In this situation the ECU cuts fuel delivery until the engine speed drops below 1600rpm or the TPS position changes to either position 2 or position 3.

    The TPS not at position 1 when the throttle plate is closed will likely result in a poor engine idle speed, engine stalling, unburnt fuel being dumped into the exhaust during engine overrun and an inability to set the ignition timing and engine idle speed correctly.

    The TPS at position 1 or the IDL and E2 terminals of the ECU shorted when the throttle plate is open more than 1.5, the ECU will cut fuel once the engine speed reaches 2000rpm and resume fuel delivery after the engine speed has dropped below 1600rpm. When the engine appears to have a rev limiter set at 2000rpm it's likely the IDL terminal of the ECU is shorted to ground somewhere.


    TPS Position 2: OFF

    When the throttle plate is between 1.5 and 70 open the TPS will not make any connection between the IDL, E2 and PSW terminals of the ECU. The ECU constantly monitors the IDL and PSW signal voltage, when both signals are at 5v the ECU knows the throttle plate is partially open.

    When engine coolant temperature is above 80C and the TPS at position 2 the ECU: goes into a closed loop operation using the feedback signal from the 02 sensor to adjust fuel injection, fully utilises it's corrective ignition advance control functions.

    The TPS at position 2 when the throttle plate is closed will likely cause a poor engine idle speed, engine stalling and an inability to set the ignition timing and engine idle speed correctly.


    TPS Position 3: PSW>E2

    When the throttle plate is more than 70 open the TPS connects the PSW terminal and E2 terminal of the ECU. The ECU constantly monitors the PSW signal voltage and when it drops from 5v to 0v (because it's been grounded by E2) it knows the throttle plate is in it's wide open position and maximum power is being demanded.

    When engine coolant temperature is above 80C and the TPS at position 3 the ECU: goes into an open loop operation ignoring feedback from the 02 sensor and instead using lookup tables to directly control fuel injection and ignition timing.



    ************************************************** ************

    That's as far as I've got, I'll come back an finish the rest as soon as I get chance.

  5. #5
    Paid Member Jay's Avatar
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    Other symptoms include delayed throttle response and the inability to set the timing correctly.

    Jay
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  6. #6
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    Thumbs up super admin

    @Texx: i'd vote for you to be a super-admin if there was such an exception..! always very helpful, with precise info on almost every other topic i've read on here.. thumbs-up my man..
    i'd repp you but the forum ghosts keep saying i have to spread repp around first..

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