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Need Help with "Stumbling" in TR could possibly be TPS switch related

Discussion in 'Boxers/TR/M' started by Veedub00, Oct 4, 2015.

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  1. Veedub00

    Veedub00 F1 Veteran
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    Jun 30, 2006
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    Troy, Michigan
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    James
    #1 Veedub00, Oct 4, 2015
    In my TR journey I have been trying to figure out why my car stumbles when I'm driving when I barely push on the pedal. Its a weird "miss" that kinda rumbles a bit. My passengers don't feel it like I do, but its always bothered me.

    So what I discovered is that when I simulate idle (jumping the 18 and 2 connections on the throttle microswitch (aka Throttle Position Sensor, aka TPS) the "stumble" goes away and is eliminated.

    So what's happening here when the car thinks the throttle plates are closed? Is there any other things I should look at?
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    26,797
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    #2 Steve Magnusson, Oct 4, 2015
    When the throttle microswitch is closed:

    1. the ignition timing is retarded, and

    2. the voltage swings supplied to the EHAs by the ignition ECUs during warm running are more limited (to limit the perceived "hunting" at idle).

    And both of those things would improve the perceived "smoothness" of operation, but it would be way bad to operate that way (and definitely not "normal"). Some questions:

    1. How does it run when warm with the O2 sensor single wires unplugged (which keeps it in open loop mode)? (Label things before unplugging so you don't get them mixed up.)

    2. What are the DC voltages on the unplugged O2 sensor single wires relative to ground during warm idle?

    3. With the O2 sensors plugged in at warm idle (closed-loop mode), are the voltages on the O2 sensor single wires relative to ground reasonably "swinging/wandering" between 0.1~0.2VDC (lean) and 0.8~0.9VDC (rich)?
     
  3. Veedub00

    Veedub00 F1 Veteran
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    #3 Veedub00, Oct 4, 2015
    ok, I'll check the 02 stuff again. I remember doing it before and was never happy with my 02 sensor readings.

    what should I be looking for in test condition 1?

    I didn't know it retarded the timing. Perhaps, its off a tooth on one of the cams.
     
  4. Veedub00

    Veedub00 F1 Veteran
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    #4 Veedub00, Oct 4, 2015
    thanks for your help. I really appreciate all the advice you give on here. I owe you a dinner if you are ever in detroit.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    26,797
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #5 Steve Magnusson, Oct 4, 2015
    Just see if it runs any differently -- it shouldn't when things are correct (and this would be with the throttle microswitch plugged in and working).
     
  6. Veedub00

    Veedub00 F1 Veteran
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    #6 Veedub00, Oct 4, 2015
    when I bought the car they were unplugged. and from the looks of it for a bit too. The idle adjustment was way crazy too. The left precat was clogged and the right precat was hollowed out already. I hollowed the cats and precat.
     
  7. ozziindaus

    ozziindaus F1 Veteran

    Aug 16, 2012
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    Sam
    #7 ozziindaus, Oct 5, 2015
    Any chance your ex-oily distributor has something to do with this?

    PS. I'll double the dinner for Steve ;)
     
  8. 365boxer

    365boxer Formula Junior

    Sep 30, 2004
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    #8 365boxer, Oct 10, 2015
    When you are still coasting forward but your foot off the throttle (gas) pedal the job of the TPS is to shut off the signal to the fuel injectors via the ecu. If you just crack open the throttle enough to switch the injectors back on you will then be injection fuel but due to the tiny throttle opening very little air is being induced. This leads to a very lean fuel air ratio and that is the rumble you can hear. Made much more noticeable due to the exhaust internals having either been removed or having decayed. If the switch has been bridged for some time that will have led to the decay off the converters as fuel will continue to be injected on over run and will line the inside of the catalyst and then burn off when the throttle has been opened again.
     
  9. carguy

    carguy F1 Rookie

    Oct 30, 2002
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    #9 carguy, Oct 11, 2015
    Hi James....the Throttle Position Switch should be physically adjusted so that it "clicks" just as the throttle plates are opening up....from what I can recall. I've been out of this game too long... :-(
     
  10. Philwozza

    Philwozza Formula 3

    Apr 23, 2009
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    Phil Worrall
    #10 Philwozza, Oct 12, 2015
    Thats correct Jeff although mine is at the end of its travel when set up correctly.


    Phil
     

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