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89 Prelude Main Relay...BIG PROBLEM!

Discussion in 'Prelude' started by jfrench428, Sep 19, 2006.

  1. jfrench428

    jfrench428 New Member

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    Sep 18, 2006
    I have been living with this problem for some time now. Last year I had and still have a problem with my ECU not supplying the proper "switched ground" for my main relay to activate my fuel pump. I since ran the "switched ground" to ground and have been running the car like that. What would make the ECU not engage the switched ground? Could the ECU be bad? The car runs great, I just don't get it. Does anyone have schematics on the ECU that might help me? Thanks for any help!
  2. 1Funryd

    1Funryd Member

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    Dec 8, 2006
    Check out this link for some common issues for your 3rd Gen Lude.



    Problem: Car wont start when its hot out, or takes a long time to start.
    If you don't know how to solder or are unconfortable in repairing your own, you can probably take it an electronics store (not radio shack) and they can do it for you. Or just buy a whole new one.
    Part Numbers for new relays:
    1988 Prelude 2.0Si - 39400-SF1-003 RELAY ASSY., MAIN (RZ-0045) (MITSUBA)
    1989-1991 Prelude 2.0Si, Si - 39400-SF1-013 RELAY ASSY., MAIN (RZ-0081) (4P) (MITSUBA)
    What you'll need:
    - Philips head screw driver
    - small flat head screw driver
    - 10mm socket
    - rachet with 6" extension
    - a soldering iron (I have a 30watt, but a 40w probably would've been better)
    - some solder
    - some time. If I had to do it again, I can get it out and back in, in about 30min. But you should probably give yourself about an hour to be safe.
    Before starting, be sure you're ready to solder or have a replacement relay ready to go (your car won't run once you remove it).
    Remove the coin tray covering the fuse panel.
    Remove the 5 philips screws holding the plastic cover under the steering column. (1 in each corner, 1 where the coin tray was)
    Unplug the 3 electrical connectors attached to the plastic cover, taking note where each one goes.
    Using the 10mm socket and the rachet with extension, remove the 2 bolts holding the fuse panel up.
    Work the panel out from under the dash. You'll have to disconnect some of the shorter wire connectors to get it all the way out.
    Unplug the connector from the main relay. Use the small flat head screw driver to press on the tab that locks the main relay onto the fuse panel and slide the relay off.
    Remove the plastic cover from the relay. You'll see the printed circiut board and all the solder points. Add a little solder to each making sure you melt the old solder.
    Put everything back the way it came out and start it up!​
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