Mod idea for constant highway TC unlock

Discussion in 'Drivetrains' started by DrewsBrews, Nov 3, 2016.

  1. DrewsBrews

    DrewsBrews FEOA Donator

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    The TC lock/unlock is extremely annoying on my '98, especially on the highway where you might crest a hill and let off the gas a little too much, causing the TC to unlock. Then you have to wait the 5sec for it to lock again. I find it extremely annoying.

    Small vac leaks might be amplifying the issue, though I believe I have largely resolved those. I don't recall if the '00 I had years ago did it as much. But 98 was the first year of the electronic control for the trans, so I figure there were probably some updates/tweaking of the programing in the years since.

    Anyway... I have a ScangaugeII so I can monitor the TPS on the fly. Idle is "17" and I've noticed TC unlocks at "19". WOT is around "91", so around 3% throttle the TC will unlock. Not much, but I seem to hit it quite often. That got me thinking...

    What if I measure the resistance difference from idle and the tc unlock point, then wire up a switch with a resistor (the same value as the difference in resistance) inline on the TPS wiring to flick on while on the highway. That way it would never go under the TC unlock threshold, keeping it locked. Would that 3% variance from the actual throttle position really cause much issue to the ECU?
  2. denisond3

    denisond3 Moderator Staff Member

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    I dont know. I wonder if he PCM might be upset at not seeing the usual variations in the signal from the TPS, and would turn the CEL on. Hopefully you will be able to let us know.
  3. DrewsBrews

    DrewsBrews FEOA Donator

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    TPS would still be operating like normal, just would have a resistor piggybacking (in series) on it to keep the resistance above the TC unlock threshold. basically every throttle position would show ~3% higher than otherwise.
  4. Pizzaman5000

    Pizzaman5000 FEOA Donator

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    Or just delete the power steering :)

    Been forever since I've put any though into load otherwise.
  5. Intuit

    Intuit FEOA Member

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    System is designed to unlock whenever engine load is calculated to be too high. Check calculated engine load. If the engine is experiencing issues, may want to run a compression check, check timing, run vacuum testing. (see Adobe Flash Player tutorial at end of article http://www.secondchancegarage.com/public/186.cfm)
  6. DrewsBrews

    DrewsBrews FEOA Donator

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    It unlocks every single time at 19 no matter the condition. fast or slow. I don't think it is much more advanced than that.
  7. Intuit

    Intuit FEOA Member

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    My assumption is this is not normal behavior for other health cars. Automatic transmission have been known to behave oddly when there's an engine problem. Just something else to consider.
    zzyzzx likes this.
  8. Gator417

    Gator417 New Member

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    Not sure if the Escorts are this way, but on some other Fords you can intercept the signal from the ecu to the tranny. Instead of messing with the tps et al, there is (maybe) one wire which controls the tc lock/unlock. If you wire a switch inline, you can force the tc to lock or stay unlocked at any time. Just a thought and it may not work at all.
    Gator
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  9. DrewsBrews

    DrewsBrews FEOA Donator

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    Yeah. That would be nice. I imagine there might be a wire since it can control the lock. However I wouldn't want it trying to down shift with the TC locked if I have to punch it in an emergency situation. Hence my idea of just nudging the tpm signal slightly.. which still gives the computer full control over the trans to unlock for shifting.

    I ended up capping off the evap purge solenoid for the moment, which seemed to be a small vac leak source. It's a little better, but still unlocks quite often on the highway. The section of highway I commute on has many shallow rolling hills. Going over them I lift enough to cause the TC to unlock every time.

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