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  1. #1
    Fuel Injected!
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    TPS reads high with throttle closed

    I have a TBI unit from a 1988 K3500 with it's stock TPS sensor. It is non adjustable with the 3 pin weatherpack style connector that sticks out at a 90 degree angle. I am using a 16197427 running $31 with BMHM (1995 7.4 auto) for a starting point. Tunerpro shows the throttle position with the throttle closed at 18%, and tops out at 88%. Is this a problem? Is my TPS incompatible with the newer computer and will this cause me any problems, or does the '7427 read the sensor default position and compensate? If I need a different sensor which one do I use?
    1995 K1500, Cadillac 500 TBI with 4L80E swap. 7427 PCM and 454 TBI.

  2. #2
    Super Moderator dave w's Avatar
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    The old style 3 pin flat and newer style 3 pin round TPS sensors used for TBI throttle bodies are ALL 0 volt to 5 volt sensors. When mixing different years of parts and different year computers it's almost always necessary to modify "SLOTS" into the non-adjustable TPS sensors. TPS voltage is VERY IMPORTANT for correct computer control of the TBI system. It is a VERY GOOD PLAN to have correctly adjusted TPS voltages, 0.50 Volts closed throttle! Open throttle TPS voltage will vary, typically 4.60 volts or above is acceptable for open throttle. There is NO NEED to adjust open throttle voltage, CLOSED THROTTLE is the only position that is adjusted.

    dave w

  3. #3
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    Just for your reference, the 88 tbi is set up roughly 80 pph @ 12 psi and the bin you are using is 70 pph @ 30 psi. If you have any fueling problems that might be something to look into.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  4. #4
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    Quote Originally Posted by myburb View Post
    Just for your reference, the 88 tbi is set up roughly 80 pph @ 12 psi and the bin you are using is 70 pph @ 30 psi. If you have any fueling problems that might be something to look into.
    I have already adjusted the cylinder volume and injector flow parameters to my setup. There isn't much more I can do until my motor is broken in.
    1995 K1500, Cadillac 500 TBI with 4L80E swap. 7427 PCM and 454 TBI.

  5. #5
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    If you have adjusted there should be no problem. Years ago I fooled with $31 and BMHM and although it worked pretty good I went back to $OE as it was a little smoother. What mask and bin were in the vehicle your trans came from. In regard to your tps problem. Are you still using the iac from the 88? If so the iac logic from the early iac and the late iac are different so is it possible your iac is closed and you have opened your throttle blades to compensate and that is where your high tps reading is coming from?
    Last edited by myburb; 07-12-2018 at 03:27 AM.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  6. #6
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    Interesting, what makes BHDF that much different? I should look into that. $OE can be made to do fan control also can it not?
    1995 K1500, Cadillac 500 TBI with 4L80E swap. 7427 PCM and 454 TBI.

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