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Thread: TPS reads high with throttle closed

  1. #1
    Electronic Ignition!
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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. In progress.

  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
    Fuel Injected!
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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
    Electronic Ignition!
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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. In progress.

  5. #5
    Fuel Injected!
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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; 07-11-2018 at 05:27 PM.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  6. #6
    Electronic Ignition!
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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. In progress.

  7. #7
    Fuel Injected!
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    In my case BHDF seemed to run my transmission better. $OE seems to be more common amongst diy. There seems to be more info and support fo $OE.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  8. #8
    Electronic Ignition!
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    I started playing around with $0E last night, I think I will go that route. I am curious about the differences in IAC logic that you mentioned. What would I need to do to correct it? I have the inline metripack style IAC, not the square weatherpack one they used later. I wish it was, I HATE pull to seat connectors.
    1995 K1500, Cadillac 500 TBI with 4L80E swap. In progress.

  9. #9
    Fuel Injected!
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    I think maybe you should first check if your iac is even working and if not what position is it in.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  10. #10
    Electronic Ignition!
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    I broke my motor in today. The original TPS read correctly in the datalog on $OE. With the stock VE table from BHDF it ran BLMs in the 80s but it ran the whole 20 minutes without incident.
    1995 K1500, Cadillac 500 TBI with 4L80E swap. In progress.

  11. #11
    Fuel Injected!
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    That is good news and glad the OE is working for you. Probably if you tweak the volume or injectors it will get you closer toideal so you can start tuning. Being as it is close to what I use if I can help just let me know.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  12. #12
    Electronic Ignition!
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    I realized I actually have the early 90lb injectors, so when I set it to 80 is was too rich. I need to change out the oil/filter and then I can run it again and set up the idle and start logging some useful data.
    1995 K1500, Cadillac 500 TBI with 4L80E swap. In progress.

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