Relieve fuel pressure before removing injectors?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 12mpg, Nov 7, 2025 at 2:18 PM.

  1. 12mpg

    12mpg Junior Member

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    About to take my injectors out for inspection/cleaning on my 2014.
    Wondering if I should pull the fuel pump relay (if I can find it) and start the car until it stalls.
    I know we don’t have a regular starter on this car but wondering if I try to start it again after it’s been stalled if it will relieve all the pressure from fuel system before removing the fuel rail.
     
    #1 12mpg, Nov 7, 2025 at 2:18 PM
  2. PriusCamper

    PriusCamper Senior Member

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    While I've not done this work before, I've not heard of the need for relieving the pressure. I'd like to see the results of undoing them without relieving pressure because I've not seen anyone complain about it being an issue and you could help confirm that.
     
    #2 PriusCamper, Nov 7, 2025 at 3:07 PM
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  3. ChapmanF

    ChapmanF Senior Member

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    I usually just take the electrical connectors off all the injectors and (while the car is all turned off, of course) tickle one of the injectors with leads from a 9V battery. It squirts into the intake, relieving the pressure.

    By the time whatever work I'm preparing to do is complete, that small amount of fuel will have evaporated and wafted around, and won't cause a flooding issue by the time I want to start the engine again.

    I used the "run without fuel pump" approach once, but of course it causes heavy misfiring on the way to finally stalling out, and because any serious misfiring in a Prius will bang the daylights out of the transmission and input shaft damper, it sounds pretty horrible and doesn't make me want to do it again.
     
    #3 ChapmanF, Nov 7, 2025 at 3:27 PM
    Last edited: Nov 7, 2025 at 3:35 PM
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  4. 12mpg

    12mpg Junior Member

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    But if the injectors are still plugged in to the fuel rail wouldn’t this still keep pumping in fuel and still have the fuel system under pressure?
     
    #4 12mpg, Nov 7, 2025 at 3:30 PM
  5. ChapmanF

    ChapmanF Senior Member

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    Thanks, I've edited my post to clarify that I have the car turned off for all work involving injectors, so the fuel pump will not have power.

    I also never restart an engine, after putting injectors back in, without doing a fuel leak test first, by making the car only IG ON (not READY) and using a scan tool active test to spin the fuel pump while watching all the injector connections for leaks.
     
    #5 ChapmanF, Nov 7, 2025 at 3:36 PM
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  6. 12mpg

    12mpg Junior Member

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    Ok that makes sense. With car turned off, the fuel pump won’t be pumping more fuel in, therefore relieving pressure from the fuel system.
    I’ll give this a shot.
    Thanks.
     
    #6 12mpg, Nov 7, 2025 at 3:38 PM
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  7. Tombukt2

    Tombukt2 Senior Member

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    Make sure the car is off remotes away from the car undo two bolts w spacers about 4 turns lift rail hear pressure release viola . Careful w injector o rings
     
    #7 Tombukt2, Nov 7, 2025 at 10:32 PM
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  8. indel

    indel Junior Member

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    Do you have a writeup of this procedure or a video?
     
    #8 indel, Nov 7, 2025 at 10:46 PM
  9. 12mpg

    12mpg Junior Member

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    Yep. I dropped a bottom o-ring and it of course disappeared down in my engine somewhere. Had to go to the dealership to buy a new one for $15.
     
    #9 12mpg, Nov 7, 2025 at 11:01 PM
  10. 12mpg

    12mpg Junior Member

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    I’m not the one you’re replying to but here’s a video I followed to clean injectors. Mine were pretty dirty.

    I used two wires connected to two alligator clips. There are two pins on the injector female electrical connector. Clip your two alligator clips to those pins. And then the other side of the wire to a 9 volt battery. I don’t think the polarity matters.
    You’ll hear the injector fire on.
    I pulsed mine for about 3 seconds, 3 times, one each cylinder.
    However, I still had a lot of fuel pour out of the fuel rail once I lifted the rail off the injectors.
    Maybe I should have done it more like 10 times per cylinder but I didn’t want to burn the injector up running it dry.
    I’d recommend unplugging your 12v starter battery so your fuel pump doesn’t fire on. Opening your drivers side door will fire the fuel pump, even with the car off.
     
    #10 12mpg, Nov 7, 2025 at 11:07 PM
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  11. 12mpg

    12mpg Junior Member

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    These were what my injectors looked like at 85,000 miles.
     

    Attached Files:

    #11 12mpg, Nov 7, 2025 at 11:09 PM
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  12. indel

    indel Junior Member

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    Thank for linking the video and your response. Should be very helpful. What about the area where injections appear in the combustion chamber? Do you need to clean that area, especially after taking the intake manifold off?
     
    #12 indel, Nov 7, 2025 at 11:19 PM
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  13. 12mpg

    12mpg Junior Member

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    After doing this for my first time… I wished I would have sprayed the engine (where the injectors plug into the engine block) prior to doing anything. I did have some crud in there and it’s almost impossible to get your hand in there to effectively wipe any crud away. Even if you are able to get your hand in there with a towel, you’ll just push whatever crud is there down into the hole where the injector plugs into.
    Also, you don’t have to remove your intake for this job. Just have to remove your air box assembly.
    Another note: 3 out of 4 of my bottom o-rings (the ones that go into engine block) stayed in the engine block. One bottom o-ring pulled out with the injector and it fell down in my engine, never to be seen again.
     
    #13 12mpg, Nov 7, 2025 at 11:27 PM
  14. indel

    indel Junior Member

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    Gotcha. I am primarily needing to do a full cleanup of the EGR system, so that's the reason I am taking the intake off. I figured might as well attend to the injectors while I am there.
     
    #14 indel, Nov 7, 2025 at 11:38 PM
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  15. 12mpg

    12mpg Junior Member

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    Nice. Yeah I just pulled my intake manifold and EGR pipe last weekend. I didn’t do the EGR valve or cooler. That part is a little more involved.
     
    #15 12mpg, Nov 7, 2025 at 11:41 PM
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  16. PriusCamper

    PriusCamper Senior Member

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    Thanks so much for this... I kinda figured there was an easier solution like this!
     
    #16 PriusCamper, Nov 8, 2025 at 12:38 AM
  17. Tombukt2

    Tombukt2 Senior Member

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    Gawd danged at 500K mine don't look anything like that just silver and green lil bit o shiet on tip. Wen I blast thru w cleaner not much happened . Not much dirt etc. oh welp.
     
    #17 Tombukt2, Nov 8, 2025 at 9:38 AM
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