TPS Strange Behaviour

For discussing how to choose sensors and create a wiring harness for all Bowling and Grippo versions of the MegaSquirt® EFI controller.
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wadehilts
MegaSquirt Newbie
Posts: 3
Joined: Tue Mar 29, 2016 8:48 am

TPS Strange Behaviour

Post by wadehilts »

Hello,
I have noticed that my TPS reading tends to vary depending on the conditions around it. Let me begin from the beginning of this problem:
  • 1. I first installed my TPS so that the throttle closed position corresponds with the absolute furthest back that the potentiometer can go (i.e. the limit of its motion). This worked fine until I noticed that the TPS liked to dip from zero to -2% before coming back above 0% and progressing upwards normally. This occurred in the first tiny bit of accelerator pedal depressing, which was giving me problems with my fuel cut on overrun triggerring prematurely.
    2. I moved the TPS sensor forward so that TPS at closed throttle = 4%. Then I zeroed it and recalibrated everything accordingly. Unfortunately, this introduced a new problem. The TPS would land at zero if I opened the throttle all the way and let it snap back. It would land at -3% or so with light throttle movements. I suspected play between my D-drive and the TPS, but using permatex goop didn't solve this issue.
    3. I also noticed that my TPS reading varies with temperature significantly. The hotter my vehicle gets, (engine bay) the more my closed throttle TPS% is. It can vary as much as 4%.
    • I'm using the TPS from a Hyundai Excel. I can find the part number. I was wondering if anyone had any ideas what this issue could be.. Perhaps my throttle body has too much play in it? Is the TPS I'm using not accurate enough for my application? I can supply pictures of the setup later, and a short datalog (the one I have now is too big to attach).
      Thanks,
      Wade
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wadehilts
MegaSquirt Newbie
Posts: 3
Joined: Tue Mar 29, 2016 8:48 am

Re: TPS Strange Behaviour

Post by wadehilts »

UPDATE: The TPS sensor I was using must have been poorly designed, damaged or defective. It was from a Hyundai Excel. A trip to the local junkyard proved the best solution. I searched among many makes and models, finding that a 1999 Nissan had a d-drive tps that would fit my Peugeot's spindle. The Nissan TPS is much better designed. It has a return spring, so that the TPS lands on the same position every time. It also seems to only vary by 0.3% or so with extreme temperature changes (60 F to full engine temp with a coolant heated throttle body).
I went from having a 14% variance with temperature and about a 2% variance in resting position to a 0.3% temp variance and a <0.1% return to resting position variance. This is well under the tolerances for a Speed Density controlled system, so I'm happy with it. My fuel cut and closed loop idle work fine now.
Wade
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