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Thread: 88 LXi not starting, no fuel, GND pin voltage offset

  1. #1
    DX User jtb_116's Avatar
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    88 LXi not starting, no fuel, GND pin voltage offset

    I'm having an issue starting my 88 lxi. I replaced the engine with one I rebuilt and have not been able to get it to start since. It cranks and has spark, but no fuel. The fuel pump does not come on unless 12 V manually applied to it. I also verified that the main relay works correctly when voltage is manually applied to the appropriate pins on it.

    I narrowed it down to the main relay harness connector. The IGN SW pin is not getting properly energized to start the fuel pump. I verified that the actual ignition switch is working correctly in each key position.

    IGN SW relative to the GND pin on the harness reads -0.5 V with key off and 0.6 V with key on
    IGN SW relative to the battery negative post reads the correct 0 V with key off and 12 V with key on
    GND harness wire reads 0.5 V relative to the battery negative terminal with key off

    I'm having trouble tracing the harness through the firewall into the engine bay. Is anyone familiar with where this wire would ground to in the engine bay. And what would cause the GND wire to have a voltage offset like this? I would think that if it was shorted it would just be 12 V. Any help is appreciated.

    Summary: GND wire in main relay harness has 0.5 V with key off and 11.5 V with key on. This is preventing the IGN SW from generating sufficient voltage to activate the fuel pump relay. Not sure what would cause this on the GND wire



  2. #2

    carotman's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    The ECU will activate the main relay.

    Make sure you get voltage at the ECU

  3. #3
    DX User jtb_116's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    So I'm testing the harness for the main relay according to the FSM

    -12-53-jpg

    The pin 5 (IGN SW) gets 12 V if I check it relative to body ground or the battery. The issue is, checking the voltage between pin 5 (IGN SW) and pin 2 (GND), there is not 12 V because the ground pin is not at 0 V. Therefore there is not sufficient voltage to activate the relay which powers the fuel pump.

    -12-52-jpg

    So I'm trying to figure out what would cause the GND pin to not be at 0 V. And where the ground pin actually routes to in the engine bay.

  4. #4
    LXi User Shane86's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    I've traced the wires back before and your main ground for the main relay is on the side of the intake manifold. Try cleaning it up or adding a extra wire to that to the firewall

    -20190521_171022-jpg

  5. #5
    2.0Si User
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    Quote Originally Posted by jtb_116 View Post
    So I'm testing the harness for the main relay according to the FSM

    -12-53-jpg

    The pin 5 (IGN SW) gets 12 V if I check it relative to body ground or the battery. The issue is, checking the voltage between pin 5 (IGN SW) and pin 2 (GND), there is not 12 V because the ground pin is not at 0 V. Therefore there is not sufficient voltage to activate the relay which powers the fuel pump.

    -12-52-jpg

    So I'm trying to figure out what would cause the GND pin to not be at 0 V. And where the ground pin actually routes to in the engine bay.
    id suspect that there is a corroded connection and/or a damaged wire some place from the readings you are getting on the ground. if your battery is 12.7 volts at rest then less than 12 volts at the relay is a pretty good voltage drop right there.

    Someplace in the book there drawings of how the wiring harness routes thru the car and all the connectors.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

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    DX User jtb_116's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    Awesome, thanks. I'd bet when swapping in the engine I forgot to attach that ground. I'll update if that was it.

  7. #7
    LXi User Shane86's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    Quote Originally Posted by jtb_116 View Post
    Awesome, thanks. I'd bet when swapping in the engine I forgot to attach that ground. I'll update if that was it.
    Yeah keep us updated on it

  8. #8
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    Quote Originally Posted by jtb_116 View Post
    Awesome, thanks. I'd bet when swapping in the engine I forgot to attach that ground. I'll update if that was it.
    The two main ones I can think of is battery negative to the case of the trans and the one from the valve cover to the front cover of the radiator. Either one of these is missing there is alot of trouble there.

    The one Shane pointed out has alot to do with the injectors its off theres trouble there.

    You may want for ow to run a separate ground from the relay post back to the battery just to get you going and get hat baby fired up.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

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  9. #9
    DX User jtb_116's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    Haven't had the chance to check the ground around the intake manifold yet, been raining everyday after work. Should be able to get to it this weekend though.

    I do know I have the ground from the valve cover to around the radiator attached.

    But even with a missing ground wire, the ground still shouldn't show positive voltage relative to the battery negative right?

    The only thing I'd be worried about with running a direct ground to the main relay harness is with the bad harness ground getting voltage I'd have to disconnect it and run a separate wire. If the bad ground is shared with other components, I assume those then will have issues.

    Thanks again everyone for help!

  10. #10
    DX User jtb_116's Avatar
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    Re: 88 LXi not starting, no fuel, GND pin voltage offset

    So finally had good enough weather to tinker around some more. Turns out, the FI harness ground was missing the bolt. I put one in and...no difference. Still have the voltage offset at main relay ground. I checked and less than 2 ohms between the FI harness and negative on the battery. IM and valve cover less than 1 ohms.

    Any other ideas?

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