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Fuel pump won't prime!

Discussion in '2nd Gen. Tacomas (2005-2015)' started by Chardonnaybee, Jun 18, 2016.

  1. Jun 18, 2016 at 2:29 PM
    #1
    Chardonnaybee

    Chardonnaybee [OP] Active Member

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    I am at my wits end with this beautiful bastard.... I've replaced the fuel pump and relay and it still won't prime when I crank it. Does anyone have any idea on what else it can be before I cave and take it in?
    Here's the story
    A few days before it completely stopped, I would have to crank it 2 or 3 times before the truck would even start. I just thought it needed a new battery.
    Battery is fine, alternator is great. I moved on to check every single fuse, all are fine. Checked the fuel pump and did not hear it priming when the key was in accessory... so I replaced the relay and entire fuel pump assembly. Nothing. The truck still will not start... EFI relay is fine. Pinched off the gas line and no fuel...
    If you have any suggestions, I would really appreciate it!
    Thanks in advance!

    3464c6ae-893b-4bbb-b3b4-2a00186e5af9.jpg
     
    Last edited: Jun 18, 2016
  2. Jun 18, 2016 at 2:39 PM
    #2
    Steves104x4

    Steves104x4 Well-Known Member

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    BUCKLE UP! It makes it harder for Aliens to pull you out of your Truck.
    I'm going to guess cam or crank sensor but I could be wrong
     
  3. Jun 18, 2016 at 3:19 PM
    #3
    maineah

    maineah Well-Known Member

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    It should run when you turn the key on to start no matter what else is wrong after it times out then there are several things that have to happen to keep it running. Have you actually had a fuel pressure gauge ?on it or you just guessing?
     
  4. Jun 18, 2016 at 3:28 PM
    #4
    Chardonnaybee

    Chardonnaybee [OP] Active Member

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    There's no fuel in the line, why would I need a fuel pressure gauge?
     
  5. Jun 18, 2016 at 5:57 PM
    #5
    maineah

    maineah Well-Known Member

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    You disconnected the line and got nothing? Have you done an ecu scan?
     
  6. Jun 18, 2016 at 6:03 PM
    #6
    RobertHyatt

    RobertHyatt You just can't fix stupid...

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    Couple of notes:

    (1) it should NOT run when the ignition is in the "accessory" position. It should run for a few secs when you put it in run, and then switch off. If the ECU sees crank pulses, it will run the pump as necessary.

    (2) how much gas in the tank? Near empty is (a) hard on the pump as it depends on the fuel around it for cooling and (b) with little fuel it can have a problem priming.

    As a debugging procedure, you can again remove the tank or bed, however you got to it, remove the fuel lines, the pump, and power it from a battery externally to see if it is running with direct 12v input. If so, hook it back up to the wiring harness (leave fuel lines off) and have someone turn ignition on and off. Any fuel spurt out?

    Now you should know whether or not the pump is good (yes, many of us have gotten a bad pump right out of the box. Not a frequent event, but not a "never happens" event either.), and if it runs with direct connection, you will know whether you get a power signal to the pump from the ECU when the switch goes to "run".

    Assuming the pump does run but no fuel comes out, you are either dry of fuel, or if you just replaced the pump, you most likely reversed the two rubber tubes (yes one is inlet, one is outlet, getting this wrong will result in no fuel delivery.) If you replaced the entire canister, you might look for a blown-off line, burst line, etc between the pump itself and the connectors on the top of the canister.

    That should get you started toward the problem..
     
  7. Jun 18, 2016 at 10:14 PM
    #7
    landphil

    landphil Wishin' I was Fishin'

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    I'd start by putting a jumper wire between the two high current pins of the fuel pump relay socket and see if the pump runs and creates flow.


    Have you tried a second transponder key? Does the blinking light below the radio go out when you insert your key in the ignition?
     
  8. Jun 19, 2016 at 5:39 AM
    #8
    maineah

    maineah Well-Known Member

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    It does run if you are trying to start the truck and it does time out if it does not get a run signal. Running a pump low on fuel will not damage it from heat they are cooled by gasoline it goes right through the pump, motor windings, brushes and all it is not cooled by the surrounding fuel. If the truck is running the pump is being cooled if it's not running it’s because there is no fuel and the ECU shuts the pump off because it does not have a run signal. The system requires about 35 PSI to run even the slightest bit of air will cause the engine to stop because the pressure will plummet, air compresses fuel does not. As far as crap on the bottom of the tank the pump is already there it does not mysteriously lower it’s self as the level of fuel drops. You can believe what you want I do have a little insight, back in the early 70’s I taught continuing education classes for Bosch just about every fuel injection system made today is based on the Bosch systems.
     
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  9. Jun 19, 2016 at 2:00 PM
    #9
    RobertHyatt

    RobertHyatt You just can't fix stupid...

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    You will find that MANY manufacturers recommend that vehicles not be continually used with very low fuel levels. If you look at a fuel pump, the fuel that is being pumped ONLY contacts the pump on the end of the motor, which is made mainly of plastic and which does not conduct heat. The remainder of the pump is the motor, which is made of metal, and immersing it in fuel definitely lowers the operating temperature. Fuel does not flow through the length of the pump, but only thru the small plastic part on top with the inlet and outlet barbs. That's not where the heat is generated.
     
  10. Jun 19, 2016 at 2:57 PM
    #10
    maineah

    maineah Well-Known Member

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    There is nothing in any manufactures users guide including Toyota about low fuel usage because how much would be too little. The gasoline goes right through the motor metal plastic etc. on it way to the fuel rail. That is why there is a sock on the bottom and a outlet on the top of the pump.
    External Bosch pumps had fuel going directly through them and they were not even in the tank to be cooled.
     
  11. Jun 19, 2016 at 8:20 PM
    #11
    RobertHyatt

    RobertHyatt You just can't fix stupid...

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    Sorry, fuel does NOT "go right through the motor". The only contact the electric motor has with fuel is the fuel sloshing around in the tank that hits the metal exterior of the motor.

    Some do have a sock on the bottom, with a straight tube from the intake on the bottom to the pump on the top. Good luck with your pump circulating raw gas inside the armature with the sparks at the brushes and such. And yes, they have brushes, these are DC motors. The heat is generated in the armature and field coils and bearings on both ends. Not inside the actual pump/vanes...

    Many more have inlet and outlet on the top however.
     
  12. Jun 19, 2016 at 8:27 PM
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    landphil

    landphil Wishin' I was Fishin'

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    Be enlightened, oh stubborn one:

    https://www.google.ca/?gfe_rd=cr&ei=dmJnV-HyIYfjiwKKwIewCw#q=electric+fuel+pump+cutaway+image
     
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  13. Jun 19, 2016 at 8:42 PM
    #13
    Jimmyh

    Jimmyh Well-Known Member

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    I agree with maineah and landphil on this one.

    Get you a gauge and a jumper wire and find out what you really have going on.
     
  14. Jun 20, 2016 at 5:37 AM
    #14
    maineah

    maineah Well-Known Member

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    My 2011 has 75K on it my 97 had a little shy of 300K I never put fuel in them until they were just shy of empty I all ways put at least 19+ gallons in the 11.
    First this, http://www.aa1car.com/library/fuel_pump.htm (nice picture) Second the fuel will not burn the O2 level is way too low to promote combustion inside of the tank and there is no O2 in gasoline. GM had issues with bad connection frying inside the tanks not a single one caught fire.
     
  15. Nov 3, 2018 at 10:46 AM
    #15
    Theshoe05

    Theshoe05 New Member

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    This is a few years later from this original post. I still wanted to provide an idea for any Tacoma owners. My issue started a few weeks ago when my fuel pump was turning on. I took the tank down and tested the pump, pump worked so I replaced the relay and the truck worked for a few weeks then it broke down again. I bought a new relay and it did not turn on. There was no power going to the pump. I disconneddis my battery and disconnected the MAFS and reconnect the battery and my truck turned on, while it was running, I reconnected the MAFS and truck turn off: no power to the fuel pump. My conclusion was a bad MAFS .
     
  16. Nov 3, 2018 at 11:02 AM
    #16
    Muddinfun

    Muddinfun Well-Known Member

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  17. Nov 3, 2018 at 2:30 PM
    #17
    maineah

    maineah Well-Known Member

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    Basically your c/opn relay is a kick in the ass, in turn the fuel pump relay turns off the signal from the c/opn via the ecu and operates at a reduced voltage through a resistor.
     
  18. Nov 3, 2018 at 2:57 PM
    #18
    Muddinfun

    Muddinfun Well-Known Member

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    Sort of, but not quite. When the fuel pump relay is energized, it transfers power from the c/opn relay from direct voltage, to an alternate path through the resistor to the fuel pump. The power still goes through the c/opn relay to get to the resistor via the fuel pump relay.
     
  19. Nov 3, 2018 at 4:19 PM
    #19
    maineah

    maineah Well-Known Member

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    It's a double pole it opens the 12 volt then contacts the resistor Both relays are are powered by B/W wire the latency in the fuel pump relay c/opn allows a short burst of 12+ volts to kick start the pump.
     
  20. Nov 3, 2018 at 4:56 PM
    #20
    Muddinfun

    Muddinfun Well-Known Member

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    OK, you win. You're wrong in minor details, but I concede.
     

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