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TPS RoC Phantom Activity In/Out of Closed Loop.

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  • TPS RoC Phantom Activity In/Out of Closed Loop.

    Hi all. Reaching out for a bit of expertise here. I have a 383 SBC with an 871 blower and Enderle big & ugly hat setup, progressive linkage. Currently running the Holley HP setup and working on getting the tune properly setup.

    I took it in to a local tuner here and there has been an on going issue with the TPS RoC constantly bouncing around and flickering values on the AE table (AE vs TPS RoC). This is occurring even with the TPS % being at zero. Unsure why this would be happening as my understanding is that if the TPS % is at zero there should be zero TPS RoC?

    TPS RoC Blanking set to 10 with the help of EFI Expert. Since the computer is picking up TPS RoC change it's throwing it out of Closed Loop thus no ECU Learning for the fuel tuning. The car idles and runs decent at low RPMs through manual tuning, but I need it to Learn and this issue is preventing it.

    First, thought was to check all of the wiring and grounds which is indeed wired correct. This was triple checked.

    Next, we replaced the TPS unit with a new Motec one and the issue persists. Now the frustration is ongoing as not sure where to look next.

    Has anyone experienced this issue before? It would seem as though the TPS is getting some sort of interference which is causing RoC signal activity. Any helpful comments would be greatly appreciated!
    Last edited by Cerrillomb; 05-28-2021, 01:35 PM.
    Mason Cerrillo

  • #2
    I went ahead and ran a datalog to show what exactly is going on. The TPS RoC value has a bunch of spike and noise even when the TPS % stays constant or relatively constant.

    I've noticed that when ignition is turned on and the fuel pump primes, this is the start of the issue. The TPS RoC will continue to bounce around until after a short time 1-2 minutes. Then the TPS RoC will go back to normal and not have any noise, which you'll see in the datalog.

    With this behavior it's almost like a capacitor in the ECU is charging up once the fuel pump primes and is leaking onto the TPS RoC circuit which is causing interference. After waiting a few minutes, it gives the capacitor enough time to fully discharge and then the noise goes away. Does this sound plausible?

    We do not have any RFI on any of the other sensors. All plug wires & Dual Sync distributor are routed away from the harnesses. Power & ground going straight back to the battery.

    Datalog Link:
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    Mason Cerrillo