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LH2.4 ECU not allowing ground signal to reach FI-System relay

posted by  Vos on  Sat Jul 27 13:09 CST 2002
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last visit: Mon Dec 21 13:54 CST 2009
[RELATED]

Hi all, my father-in-law and I have finally finished our conversion project (1990-745 B230F Rex -> B230FT LH), and the car runs great! ...but only under one condition: when I manually ground the black-yellow contact at the FI-System relay in the dash.

The contact point is listed in TP-31571/1 (the volvo wiring manual for this year) as a ground signal to the relay that is controlled by the ECU. When I manualy ground it the fuel pumps run and everything is happy with the world! But, without my intervention the pumps fire once during start-up and then do not get the FI relay signal that lets them run. It appears that the ECU is not allowing the ground to occurr...

I have heard that in the absence of certain sensor signals the ECU does not let the FI relay activate the fuel pumps, so that the pumps don't run when the engine is not running (a safety feature I suppose). But I don't know which signals would result in this effect...

Any suggestions? Or, any extra info I could give to prompt for any suggestions?

THANK YOU! (all caps since I am desparate:)
--
Two '98-S70s and One '90-745. My First Car: '74 244DL Gone But Remembered!








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    LH2.4 ECU not allowing ground signal to reach FI-System relay

    posted by  pjmcgnns on  Sat Jul 27 14:25 CST 2002
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    last visit: Wed May 2 05:23 CST 2007
    [RELATED]

    I'm pretty sure the ECU needs to get a signal that the engine is spinning if it is to continue powering the pump. Typical signals used are hall effect sensors from the ignition ie something that reads the crank or flywheel and puts out a square wave. They can go directly to the ECU or sometimes first to an ignition module whgich then sends a "i'm spinning" signal. Hope this helps.

    PJM








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    LH2.4 ECU not allowing ground signal to reach FI-System relay

    posted by  rhaire on  Sat Jul 27 13:23 CST 2002
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    last visit: Mon Aug 4 10:16 CST 2014
    [RELATED]

    "Loss of fuel pump ground" is a failure mode known for the Bosch 561 ECU. Replace it with a 951 (NOT a 591) and your car should start right up. Most 89-on normally aspirated 240s or 740s are candidate donors.








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      LH2.4 ECU not allowing ground signal to reach FI-System relay

      posted by  rhaire on  Sat Jul 27 15:21 CST 2002
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      last visit: Mon Aug 4 10:16 CST 2014
      [RELATED]

      Sorry, I did not realize it was a turbo. I have never seen a post about a failed 563 in my years of Volvo on the web. I think it would be a real rare event, and the first to come to my attention. I have a 563 in the 780 so I will be taking notes.








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        LH2.4 ECU not allowing ground signal to reach FI-System relay

        posted by  dick on  Sat Jul 27 15:54 CST 2002
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        last visit: Sun Aug 3 15:24 CST 2014
        [RELATED]

        Did have a 563 fail on a 90 turbo a couple years ago. Was the no fuel pump bit, but it would not even fart--this at least runs in position III , key that is. Sort of charges the system enough to start, but as soon as getting out of III and going to II the pump quits.

        dick








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          LH2.4 ECU not allowing ground signal to reach FI-System relay

          uid 55's pic
          posted by  john sargent on  Sat Jul 27 17:04 CST 2002
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          last visit: Wed Oct 22 09:07 CST 2014
          [RELATED]

          The Bosch systems always power the fuel pumps in the engine start position of the key switch. For the fuel pumps to keep running, the ECU must see a signal input from the ignition system. I don't know which one they used.
          --
          john








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      LH2.4 ECU not allowing ground signal to reach FI-System relay

      posted by  dick on  Sat Jul 27 15:01 CST 2002
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      last visit: Sun Aug 3 15:24 CST 2014
      [RELATED]

      This has a 563 in it. Same deal??

      This is son's-in-law and my project.

      dick








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        Found the problem!

        posted by  Vos on  Sun Jul 28 08:10 CST 2002
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        last visit: Mon Dec 21 13:54 CST 2009
        [RELATED]

        We found the problem! I 2x-checked all of the EZK and ECU contacts, measuring voltage or resistance depending on the signal, and they all were as expected except the black-yellow lead that of course goes from the ECU to the FI-system relay...rather than providing a ground it was actually generating a voltage! We removed the ECU and hooked up an extra one that we had in the workshop and it worked great! It turned over and stayed on, and I even drove the car home today...(first time its left the garage in over a month!).

        It appears that the 563 ECU an internal problem after all...

        Thanks for all the advice!
        --
        Two '98-S70s and One '90-745. My First Car: '74 244DL Gone But Remembered!







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