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  1. #1

    Default Looking For Auto. Elec. WIZARD

    I have a '97 Cheyene . Been having fuel system issues. After two fuel pumps and new relay,truck will die while driving. Ive figured out the relay is getting hot. When relay was replaced ,I noticed around one terminal plastic was melted on both relay and fuse block. Im sure this is my problem. The QUESTION is: WHAT caused it? HOW do I fix it ? This seems to be a common problem ,But I haven't seen anyone explain it , or say how to fix it , only fix symptom. HELP ME MR.WIZARD!!!!!!!!
    King Nothin

  2. #2

    Default

    Obviously melted plastic is caused by heat, to that end, heat is caused by: 1- load, 2- loose/dirty connection and/or pitted relay contact.
    In your case the whole situation could have started in the relay and the heat radiated out to the holder contact, or the opposite. The heat could have started in the relay socket terminal(being a loose contact) and radiated to the relay......

    Either way you are going to have to replace the contacts/internal connections that the relay plugs into or else you are not going to resolve anything.
    While you are at it, if you can find a local electrical guru that can check for any damaged wire in the loom going to the fuel pump, and check the current load for the pump. It's probably ok since you didn't blow any fuse, but you never know.....
    2010 Silverado LT 1500 5.3L 4X4
    '95 BMW K1100LT
    '97 BMW K1100LT

  3. Thanks King Nothin thanked for this post
  4. #3

    Default Thank you Mr.A

    Thanks for your reply. Some different words, but pretty much, the same I've already heard. I know I have to replace the contact in fuse block. that's fixing the symptom. But all in all your reply was insightful about the cause. The relay supplies power to fuel pump, until the engine starts. Then the power is supposed to come from oil pressure sending unit. So why does relay get hot, and kill the engine ?
    King Nothin

  5. #4

    Default

    Quote Originally Posted by King Nothin View Post
    The relay supplies power to fuel pump, until the engine starts. Then the power is supposed to come from oil pressure sending unit. So why does relay get hot, and kill the engine ?
    I have not seen a technical schematic on this specific fuel pump circuit so my comments here are basic electrical theory(as a professional electrician). I think the relay powers the pump all the time, BUT the signal that tells the relay to operate comes from the computer, and the computer will trigger it based upon different situations.

    Turn the ign key on, ecu signals the pump relay to energize the pump and prime the system. Then when the ecu sees the engine turning either by oil pressure signal, or a crank rotation sensor input, it will then energize the pump relay again to start the pump for engine run.

    Your oil pressure sensor will send it's pressure signal to the ecu computer so then it can send a value to your dash gauge, and also do what ever else it's programmed to do with a "valid proof of pressure" signal.

    Not saying this is exactly how this system is designed, but from an electrical standpoint, it is a logical sequence of operation.
    This is how my motorcycle efi fuel pump circuit is designed, prime on ign on, then pump relay on when the crank rotation sensors see rotation.
    2010 Silverado LT 1500 5.3L 4X4
    '95 BMW K1100LT
    '97 BMW K1100LT

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