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switching efi 87 to carb fuel gauge issue

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by gn4u2c, Oct 18, 2005.

  1. gn4u2c

    gn4u2c 1/2 ton status

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    this is an 87 pickup with dual tanks ,

    I'm helping putting a 400 sb in for friend and he wants to use a 750 edelbrock .fine I say. all in and runs fine.
    Problem fuel gauge is pegged all the time he used a mechanical pump and older non efi pickups in the tank.
    There are 2 wires that go to each pump (old efi units) so how the heck do we make the gauge in the dash work correctly ??

    Does he need a whole 86 harness or what ?? It still has a selector valve also
    Thanks !
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    No difference in the sending unit gauge wiring, one wire no matter the year, additional wire for TBI is the pump 12V.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If the gauge is pegged then the wire is grounded somewhere. Go check for any pinched wire to the sender along the frame rail or any bare wire touching the frame somewhere.
     
  4. alec78

    alec78 1/2 ton status

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    What do you mean by pegged? If you mean the same as 3 o'clock then there is an open in the circuit. If you mean pegged on empty then it is short to ground.

    GM fuel sending units have been the same for YEARS! 0 ohms is empty and 90 ohms is full. In english that means grounded (0 ohms) is empty. An open (break) in the circuit causes the max ohms possible which is greater than 90, so the gauge winds up about 3 o'clock (as if it were a clock).

    A quick way to test if it is the sending unit is simply pull the wire that goes to the sending unit and ground the gauge side not the tank side. Make sure it is not the other wire that was for the pump. The gauge should read empty. If it does the the sending unit has seen better days OR the tank ground is missing. If nothing changes on the gauge then the open is somewhere between the gauge and the wire to the sending unit.

    If you want me to explain this a different way PM me and I'll do a better job. After all its 4:00 AM and I'm on my 10 straight day (night) at work. I'm not really sure I'm reading CK5 or just dreaming about it :crazy:
     
  5. gn4u2c

    gn4u2c 1/2 ton status

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    thanks will check it out. there is a pink and a gray wire going the sending unit we have the correct ends now to crimp on for the non efi sender . any one know what wire to use don't want to melt anything. :D
    cannot belive he tossed both efi pickups THEY were good!!!! those are expensive + I could have seen what wire went to pump and what wire went to the level sender AHHH :doah:
     
  6. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    IIRC, pink is the 12v feed to the EFI pump
     

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