Bad ECU?

Discussion in 'Modifications And Maintenance' started by SubeN'Siren, Apr 7, 2017.

  1. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    02 WRX MT,

    Ran out of gas, put gas in, it started, ran for a mile, died, then restarted, made it home, there she sits.

    Turns over all day long, but no fuel pressure at all.

    No power to fuel pump, relay appears to be working.

    Scan tool will not connect.

    All dash lights etc work.

    Bad ECU, or something else?
     
  2. belalegosi
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    belalegosi Well-Known Member

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    Sounds like something else
     
  3. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Thanks.
    Care to elaborate why you think that?

    I'm gonna try a different scan tool tonight, though the one I have has worked for 10 years or so.

    Perhaps the fuel pump controller?
     
  4. joebush44
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    joebush44 Well-Known Member

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    I would suspect the fuel pump before the ECU. Did you check to see if you have power going to the white molex connector on top of the fuel sending unit. If no power there, then I would agree with your suspicion about the FPC going bad if you're certain the relay is good.
     
  5. Chux
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    Chux Well-Known Member

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    ECUs very rarely fail...

    Start with fuses, test the power wires at the ECU and OBD II port etc.
     
  6. phi11
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    phi11 Well-Known Member

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    Check the main wiring harness under the hood to make sure the the plugs are fully snapped together.
     
  7. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    How many volts should the fuel pump controller be putting out during prime?
     
  8. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    The people at the parts store said that a scan tool won't connect if there is no check engine light.
    Is that true?
    I thought in states where you need to pass emissions tests they hooked up, and you had to light up green, or something like that.
     
  9. tangledupinblu
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    tangledupinblu Event Coordinator Staff Member

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    Mine connects without codes. Just says 0 codes or no codes detected, depending on which one.
     
  10. MrBlue
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    MrBlue Member

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    My o3 reads thru AP, the other 3 subies all show linked with no codes, key on to establish link access( oriley's obd2 scantool )
     
  11. retreif
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    retreif Well-Known Member

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    I think just replace the fuel pump. I'm pretty sure I have one floating around. I'll check. I don't understand how running out of fuel would affect the ECU. Does seem more likely to screw up the fuel pump.
     
  12. retreif
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    retreif Well-Known Member

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    I have two, one out of a 2004 WRX, other out of a 2011 WRX. Both worked when pulled. Let me know if you want them.
     
  13. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    I agree with your thought process, retreif, I actually thought the same thing initially, so I went ahead and put a new walbro in.
    (Wanted one anyway)
    Tested on the bench, the old pump worked great...

    Power at the relay, and a whopping 1.9 volts at the fuel pump controller.

    My gut says ECM, being my obd will not connect...I'd rather have it be the fuel pump controller, but I don't think I'm getting spark or maybe injectors either.

    (I ran the fuel pump a while by jumpers, and the car still wouldn't fire)
     
  14. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Main harness...
    Under the fuse box?

     
  15. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    There is power and ground to the obd port, though my scan unit connects poorly, turns on, but will not connect.
     
  16. phi11
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    phi11 Well-Known Member

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    Left hand side where the engine and transmission mate.
     
  17. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Only getting 1.9 volts to/from the contacts on the main relay(coil is getting full battery power), corresponds with the 1.9 volts at the ECU, and 1.9 volts out of the fuel pump controller.
     
  18. belalegosi
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    belalegosi Well-Known Member

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    I don't have a schematic with me now and I'm not certain which wire in particular you are probing but...
    You should be getting over 10V at the fuel pump controller. The fact that you are measuring 1.9V suggests you are shorting to ground somewhere.
    The OBDII port has a 12V line on it that it needs (if I remember right).
    Do you have mice issues? Check your fuel pump harness, see if it rubbed or got chewed up.
     
  19. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    The obd port has power.
    The ECU, main relay, and FP relay are only getting 1.9 volts to work with (relay coils are getting full battery power)
    The wire that is supplying the 1.9 volts is blue with red stripe.
    The fuse is fine.
    Measuring resistance to ground the fuse holder associated with the red/blue is somewhere over 10k ohms, compared to other circuits, that show fractions to single ohms.
    Leads me to believe bad connection somewhere.
    No chew marks anywhere I can see.
     
  20. belalegosi
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    belalegosi Well-Known Member

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    Don't have much time now, hope this helps.

    upload_2017-4-10_21-17-12.png
     
  21. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Yeah, I was studying that diagram, over on the right, where does that line B go?
    E/G(TB)-10
     
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  22. belalegosi
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    belalegosi Well-Known Member

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  23. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Thanks for the help everyone.
    I am still struggling with this issue.
    Had a glimmer of hope just now...

    Had the key turned on without the fuel pump relay, noticed the CEL was lit, and was able to connect to the ECU...No codes found.
    Turned it over,and it started with the fuel in the lines.
    Thought maybe that relay, which I have already tested over and over, was just bad enough to screw with things.
    Went and got a new one.
    Didn't work, and the ECU won't connect with or without the fuel pump relay in.

    Almost seems like there has to be a loose connection somewhere.
    :banghead:
     
  24. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Checking voltages at the relays yesterday, I was getting the same results at first, 1.9v at blue/red, and yellow/blue, and then out of nowhere, the fuel pump kicked on, and I had full voltage on both.
    However, it wasn't right, the fuel pump stayed on for a few minutes, (vs the typical brief prime), and instead of the typical whine, it was making a flapping noise.
    Still wouldn't start, and ECU would not connect to obd scan tool.
     
  25. JasonoJordan
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    JasonoJordan Well-Known Member

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    Possible that your fuel pump coil is shorted and pulling down the voltage?

    Try disconnecting the fuel pump electrical connector and see where your voltage is at then.
     
  26. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Well, I'm pretty certain it is a broken or shorted wire somewhere.
    The yellow/blue- blue/red on the main relay are only reading 1.9 volts no matter what is plugged in downstream of there.

    I was able to make the car run by running a small jumper from yellow/red to yellow blue(on the main relay), and the car fired right up.

    Now I just need to figure out where I'm losing the power.
     
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  27. SubeN'Siren
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    SubeN'Siren Well-Known Member

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    Unplugging things on the yellow/blue circuit...
    Unplugging the MAF and Waste gate solenoid, the 1.9 volts went up to 2.4.
    Unplugging the big brown connector by the battery (where the yellow/blue turns to red, and goes to the injectors), it goes up to 8 volts.
    Wondering if it could be a shorted injector or injector wire.
     
  28. retreif
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    retreif Well-Known Member

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    I think I have light blue injectors. I'll look tonight if you are interested. Seems like you are getting closer.
     

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