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Thread: Car cranks, won't start. Suspected fuel pump wiring issue. (SOLVED: ground issue)

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    Car cranks, won't start. Suspected fuel pump wiring issue. (SOLVED: ground issue)

    The other day I started my car (2015 mirage) and she started and ran for about 30 seconds, then she sputtered and died. I tried starting her again and she cranks fine, but won't start. After some testing and listening, it's clear the fuel pump isn't running. I popped the access cover under the back seat and there's low/no voltage on the red wire of the 5 pin pump connector. I also swapped the pump relay for a known good one, and that didn't make a difference.

    I'd prefer to fix this without taking it to a shop, so I have a few questions for those more knowledgeable than me:

    Am I correct that the red wire should be at battery voltage for a second or two when you turn the key to run? Does that happen even when the plug is disconnected from the pump, or is there some form of protection that requires the pump to be plugged in?

    Is there a fuse for the fuel pump as well as the relay? If so, where can I find that?

    What's the pathing of the fuel pump wires, and where would be the best places to test for continuity?

    What areas do you think would be most likely to find corrosion or a break in the wire?

    Thanks in advance for any help or advice!

    Edit: I just tested across the relay socket, and I'm getting low/no voltage across both sets of pins.

    Edit 2: It was a fuse. Fuse 3 (10A) in the driver fuse box. It's only labeled as "engine icon".


    Last edited by RavenMirage2015; 09-11-2020 at 01:21 AM.

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    Quote Originally Posted by RavenMirage2015 View Post
    The other day I started my car (2015 mirage) and she started and ran for about 30 seconds, then she sputtered and died. I tried starting her again and she cranks fine, but won't start. After some testing and listening, it's clear the fuel pump isn't running. I popped the access cover under the back seat and there's low/no voltage on the red wire of the 5 pin pump connector. I also swapped the pump relay for a known good one, and that didn't make a difference.

    I'd prefer to fix this without taking it to a shop, so I have a few questions for those more knowledgeable than me:

    Am I correct that the red wire should be at battery voltage for a second or two when you turn the key to run? Does that happen even when the plug is disconnected from the pump, or is there some form of protection that requires the pump to be plugged in?

    Is there a fuse for the fuel pump as well as the relay? If so, where can I find that?

    What's the pathing of the fuel pump wires, and where would be the best places to test for continuity?

    What areas do you think would be most likely to find corrosion or a break in the wire?

    Thanks in advance for any help or advice!

    Edit: I just tested across the relay socket, and I'm getting low/no voltage across both sets of pins.

    Edit 2: It was a fuse. Fuse 3 (10A) in the driver fuse box. It's only labeled as "engine icon".
    Are you sure it's not flooded?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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    I'm not sure if you saw the edits before your reply but it was definitely just the fuse, it's running again now. When it first happened I waited a few hours and tried starting it again, and it did the same crank/no start.

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    Still Plays With Cars Loren's Avatar
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    Make sure you carry a spare fuse, and if it happens again... you've either got a failing fuel pump that's loading the circuit, or a power wire intermittently shorting to ground somewhere.

    Fuses don't often fail for no reason.

    The Mitsubishi factory service manual can be downloaded if you want to dig and see what that fuse feeds besides the fuel pump (if anything). 10A doesn't sound big enough for the fuel pump, though. I wonder if that's the fuse for the ECU or maybe the control circuit that switches the relay?
    Simplify and add lightness.

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    Yep, the first thing I did after I got it running was get a box of spare fuses so I'm not stranded again. I tried digging through the service manual when I was initially troubleshooting but I didn't really find anything useful. I might give it another look later tonight if I need something to do.

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    I just looked over the wiring diagrams, supposedly fuse 3 only controls the ignition coils. I'm not sure why I was seeing issues with the fuel pump voltage, a part of me wants to try testing everything again now that the fuse is replaced to see if I just suck at measuring or if it actually is somehow related. I listened for the fuel pump, I had someone listen through the fill tube, and there was no voltage I could measure at the pump, but I guess it's possible the pump is even quieter than I thought, and maybe I didn't have a good connection with my test leads. I'll try again tomorrow to see if that fuse made a difference.

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    Still Plays With Cars Loren's Avatar
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    Fuel pump logic can be complicated, it's all controlled by the ECU. So, the fact that it wasn't firing could have something to do with it.

    The FP won't just constantly run when the ignition is on, either. You'll usually get a very short priming pulse just to build pressure, then it won't come back on until you're either cranking, or it senses airflow.

    At least if it's coil pack wiring, it's a little easier to see and trace. All right there under the hood.
    Simplify and add lightness.

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    Quote Originally Posted by RavenMirage2015 View Post
    I just looked over the wiring diagrams, supposedly fuse 3 only controls the ignition coils.
    No spark would do it too. Just going for the easy stuff as there's not many reports of fuel pump problems reported here.

    What kind of gas are you using?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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    Quote Originally Posted by Loren View Post
    At least if it's coil pack wiring, it's a little easier to see and trace. All right there under the hood.
    Yeah, that's true. Hopefully if there's a short it's an obvious one.

    Quote Originally Posted by Eggman View Post
    No spark would do it too. Just going for the easy stuff as there's not many reports of fuel pump problems reported here.

    What kind of gas are you using?
    I've been switching between regular and pure gasoline, usually from Holiday Oil or Maverik. Currently it's full of pure gas from Holiday Oil.

  10. #10
    Loren nailed it. Checking for voltage at the pump can be tricky. You won't always have voltage when you think you should. Then look at ford logic with variable voltage fuel pumps to regulate fuel pressure.... So it sounds like you have a coil or wiring issue possibly?

    There have been some cars with pinched or broken wires along the wiring harness on the top front of the engine where they're secured with zip ties.

    I've also seen problems with the lowest connector behind the drivers kick panel. I can't say if any of those wires in there run to the front though..

    But the easiest place to start would be checking for codes and if there are multiple ones stored find out which one/s is most recent and go from there. Or plug in a 30amp fuse and follow the smoke trail.


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


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