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Thread: TPS Voltage Out of Spec

  1. #1
    Hybrid booster
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    TPS Voltage Out of Spec

    Hey guys,

    I'm hoping somebody might have some experience with this, or a solution.

    Engine: 1989 TII

    I've been chasing a misfire or "burble" that only happens during idle, or no load cruise.

    I discovered that my TPS reads 1.23v at closed throttle, but it should be between .3v-.9v.

    I ordered an original Mopar TPS from Marty and popped that one on, it ALSO read 1.23v.

    At this point I thought perhaps my idle screw had been messed with at some point in the car's life, resulting in the throttle being slightly too open when resting.

    I went through NAJ's throttle body cleaning and base idle calibration steps. I had a multi-meter backprobing the TPS while doing these steps, and I was never able to bring the voltage within range. The engine died while attempting this (backing the idle screw off). I even just left the key on to get a voltage reading and backed the idle screw out until it was no longer making any adjustment to the throttle plate at all, and voltage was still too high.

    Went through the base idle procedure again to make sure my AIS was calibrated. But, we're back to where I started.

    For the life of me, I cannot understand why my TPS voltage is running too high. I do have a FWD Stage III calibration, and I'm starting to wonder if that's the problem. Unfortunately, I don't have any other SMEC to try.

    Please tell me somebody has a solution for me..I feel like I've exhausted all of the options I'm aware of. This issue is driving me insane lol.

    Thanks,
    -Zach

  2. #2

    Re: TPS Voltage Out of Spec

    Starting at the basics.

    Did you back probe the 5v reference circuit confirm that?

    Did you back probe the ground circuit and confirm it is staying at 0v and not floating up...

    How does the sweep of the throttle look on the TPS signal line? smooth steady increase? Erratic? How is the signal at WOT?

    Has the throttle body been cleaned? (ie. no carbon holding it open.)

  3. #3
    Hybrid booster
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    Re: TPS Voltage Out of Spec

    I'll check the 5v reference and ground and get back to you on that. The sweep itself seems to be fine, here's a link to a video of it.

    I just took the throttle body off and gave it a very thorough cleaning. Throttle response actually seems to be a bit more snappy, but it didn't change the TPS voltage.

    https://photos.app.goo.gl/xR4V6H2wDAZbwCUB9

  4. #4

    Re: TPS Voltage Out of Spec

    Closed TPS voltage-high not withstanding; am I correct in assuming the new sensor did not fix the off idle and light cruise stumble and misfire? Or are you now just concerned about the high voltage?
    best 1/8 ET-6.16 sec. best 1/8 speed-119.70 Best 1/4 MPH 145.5, Best 1/4 ET 9.65 sec. 8 valve NO NITROUS!!

  5. #5

    Re: TPS Voltage Out of Spec

    I did not see the sensor sweep vid. I wont sign in to google. But if you are watching it on a scan tool it is very likely the scan tool's update rate is not fast enough to catch a glitch.
    I have found many a mopar tps glitchy at certain opening angles but could only find the bad spot with a lab scope. could not detect it with scan tool sweep.
    also, check the sensor voltage with your dvom at the sensor connector, dont just look at the scan voltage as they may be different.
    best 1/8 ET-6.16 sec. best 1/8 speed-119.70 Best 1/4 MPH 145.5, Best 1/4 ET 9.65 sec. 8 valve NO NITROUS!!

  6. #6
    Hybrid booster
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    Re: TPS Voltage Out of Spec

    New sensor did not make any difference to the misfire, and also has the exact same voltage reading at closed throttle (about 1.23v)

    And that's fine about the Google thing. The video shows my multimeter readout while directly backprobing the TPS connector and manually, slowly, opening the throttle by hand. No detectable issues there.

  7. #7
    turbo addict
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    Re: TPS Voltage Out of Spec

    Hey Zach,
    I was just thinking about the high voltage at closed throttle for some reason. Is it possible that someone altered the throttle body set screw? I have a feeling that is what is happening. The throttle blade is opened further than it is supposed to be, because someone in the past turned the set screw to increase idle speed. It is probably holding the TPS from fully closing.
    Todd

  8. #8
    turbo addict
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    Re: TPS Voltage Out of Spec

    Todd he's gone through adjusting the throttle set screw trying to get the reading down and it's still reading high.

    Take the tps off the throttle body but leave it plugged in. Does the voltage still read high or it's it within spec?

  9. #9
    turbo addict
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    Re: TPS Voltage Out of Spec

    Quote Originally Posted by GLHNSLHT2 View Post
    Todd he's gone through adjusting the throttle set screw trying to get the reading down and it's still reading high.

    Take the tps off the throttle body but leave it plugged in. Does the voltage still read high or it's it within spec?
    I must have missed that Jay. Did Zach list what the the 5 volt input voltage actually is? I suspect it is slightly more than 5 volts. SMEC is suspect then IMO.

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