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Thread: P5 Fuel Pump relay burnt pins

  1. #1
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    2001 Mazda Protege LX 2.0

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    P5 Fuel Pump relay burnt pins

    Hi All, hope someone has had a similar issue and can help me troubleshoot. Just picked this car up a couple weeks ago. Started having issues starting, narrowed it down to the fuel pump relay. Pulled it and there was some charring. Not super bad, replaced it and itís working for now. If I have a bad ground thatís causing this to fry, whereís the best place to start looking? Donít want to cook a harness or another relay if I can help it. Thanks in advance for your help.

  2. #2
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    I found this in my wiring diagrams..



    I would think that the charing would be caused from arcing right at the pin connections in the fusebox.

    The relay and connections are 16 yrs. old.
    Dirty/corroded connections create heat.

    Your new relay would have new pins but the connector might be charred as well.
    You might want to spray it down with electrical contact cleaner and plug your relay in and out a few times to help make better contact.
    Last edited by pcb; 09-08-2018 at 08:17 AM.
    The Diagram Dude

  3. #3
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by aross1974 View Post
    ... If I have a bad ground that*s causing this to fry, where*s the best place to start looking?
    The fuse box is entirely positive inside with no ground.

    If there was a bad ground I would think the charring/arcing/heat would be at the bad ground point, not inside the fusebox.
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  4. #4
    The Diagram Dude pcb's Avatar

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    PS.. They do have these special files to clean electrical contacts but they are expensive.

    I made my own by folding a small piece of 1200 grit sandpaper over a few times or glueing a small piece to a thin or round piece of metal.



    PSS.. If you use a file or make your own, make sure it's not too thick or it will spread open the terminals and your pins won't make contact.
    Last edited by pcb; 09-07-2018 at 05:39 PM.
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  5. #5
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    Quote Originally Posted by pcb View Post
    The fuse box is entirely positive inside with no ground.

    If there was a bad ground I would think the charring/arcing/heat would be at the bad ground point, not inside the fusebox.
    ^Not necessarily; there is current flowing through the entire circuit, so any component within that circuit path is subject to arcing. Most likely points for arcing/charring/corrosion are those points that by design are serviceable & removable connectors (i.e. relay sockets/relay pins). Also, since the fuse block is largely plastic, and its terminals are rather thin metal, it doesn't handle excessive heat well - hence the charring.

  6. #6
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Pete_89T2 View Post
    ^Not necessarily; there is current flowing through the entire circuit, so any component within that circuit path is subject to arcing. Most likely points for arcing/charring/corrosion are those points that by design are serviceable & removable connectors (i.e. relay sockets/relay pins). Also, since the fuse block is largely plastic, and its terminals are rather thin metal, it doesn't handle excessive heat well - hence the charring.
    Agreed,.. The charing would occur at the bad connection. In this case the relay and it's connector.

    But a bad ground wouldn't create a bad connection in the fusebox.
    The power would be running through it anyway. A bad ground would just mean the relays would be clicking on and off repeatedly which would give more symptoms than just the fuel pump relay.

    I believe the problem lies within the relay and it's connection specifically.


    To the OP...
    Some dielectric grease on the pins and the connectors in the fusebox can help preserve the connections and help prevent corrosion and arcing.
    Last edited by pcb; 09-11-2018 at 03:23 PM.
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  7. #7
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    Thanks guys. Used dielectric greaseputting the new one in. Now to get a fog lamp relay out from under the dash...

  8. #8
    The Diagram Dude pcb's Avatar

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    The connectors tend to dry up and get stuck together.

    If it were me I'd make sure the tab is pushed in and gently take an adjustable pliers to it.
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