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Fuel Pump Drains Battery HELP!

Discussion in '1st Gen Tundras (2000-2006)' started by colo4x4xj, Jan 18, 2023.

  1. Jan 18, 2023 at 2:33 PM
    #1
    colo4x4xj

    colo4x4xj [OP] New Member

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    Hi all, long time lurker and first time poster here. Hoping somebody has had this happen before, all the research I have done on this platform and other tundra platforms has been fruitless. So here it goes-
    03 Tundra AC 4x4 SR5, upon shutoff I can hear a hum coming from the engine bay (fuel pump?) that will drain the battery. When I pull the fuel pump relay the hum stops but there is still a high pitched, barely audible tone that does not stop until I pull the EFI relay. I have replaced the three fuel relays a few times previously and that has helped up until yesterday. Went out to a completely dead battery and when I connected jumper cables, the fuel pump hum started right up again. So this morning I went down to the parts store to get three new relays and a new battery. But that didnt work this time. The fuel pump still runs with the keys off but will stop once I turn the key on. When i try to turn it over she runs rough for a second or two and then sputters and quits.
    So far i have done:
    New relays and battery, checked all fuses in the engine bay and dash, opened up the ECM and checked for water damage, disconnected the battery for a prolonged period of time and reconnected. Kinda limited on resources, my multimeter is far away and Im 12 miles from the closest town and 30 from the nearest parts store.

    Thanks in advance
     
  2. Jan 18, 2023 at 2:54 PM
    #2
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    First of all, per Toyota's fuel circuit documents, the fuel pump should only be on in two main cases:
    • Key is turned all the way to the START position (i.e. engine is turning over)
    • Crank Position Sensor notified the ECU the engine is running while key is also in ON position.
    If you're saying your fuel pump is ON outside of the two cases above, I personally think you have a problem. Like ... Maybe the relay you bought at the store is the wrong fuel pump relay, and it's completing the circuit when it shouldn't be. Relays aren't universal. One member already found out the hard way recently not to trust 'universal' relays from the local auto parts stores for starter/fuel. Another found out the hard way with a generic relay for their heated seats, after their seats would never turn off. In general it's a mistake to buy non-OEM parts on these trucks, especially lower ball joints and anything electical.

    Hum in the engine bay shouldn't be the fuel pump. It's in the gas tank.

    High pitch whine in the engine bay is often the security piezo, which is usually hanging off the harness that comes out next to the brake booster.

    I'm not saying your fuel pump relay isn't bad. But I'd revert back to the original OEM relay to get back to square 1.

    Do you have any way to measure fuel pressure before the fuel rail?

    Are you familiar with the fuel system, and how it works? This video may help, but just know, it has misinformation in it, the fuel pump is NOT normally on when the key is in the ON position.

    Here's the fuel pump circuitry if you want to understand how the fuel system works.

    Here's a link to some diagnostic videos that may help you diagnose starting issues:
    https://www.tundras.com/threads/2005-ac-wont-start-fuel-system-problem.113385/#post-2921783
     
    Schcoman and FrenchToasty like this.
  3. Jan 18, 2023 at 3:07 PM
    #3
    colo4x4xj

    colo4x4xj [OP] New Member

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    Thank you very much for the info! I am going to read up on your links and go back to an OEM relay. Unfortunately I dont have a way to measure fuel pressure where I am. Would it change things if I hear the pump running in the tank as well as something running on the engine? Ive got a video but it sounds like two different pumps are running. Its been hard to pinpoint exactly where in the engine bay but its around the intake manifold/fuel rail/injectors area and stops when the relay is pulled.
     
  4. Jan 18, 2023 at 3:29 PM
    #4
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    If you're 100% positive the fuel pump is running, while the key is out/off, that's a problem.

    You'd need a DMM to pop out the relay and see if any of the pins are always-hot. I can't remember, and those startup videos are for a model a couple years older than yours (same generation, though) but the general overview should be right.

    Big thing is understanding the relay is supposed to take the hot input lead, and push it either (A) direct to the pump at full voltage for "hi speed" mode, or (B) through the fuel resistor (opn/c?) which dumbs down the voltage making the pump run in "low speed" mode.

    If your pump is running at all times, except when the fuel pump relay is out, that to me is a great symptom to run with diagnostically.

    As far as what else is buzzing, I ... dunno. I'd need to hear it. But you should be able to put a steth or rod or something on the fuel rail to see if that's where it's coming from.
     
  5. Jan 18, 2023 at 7:02 PM
    #5
    colo4x4xj

    colo4x4xj [OP] New Member

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  6. Jan 18, 2023 at 7:22 PM
    #6
    NickB_01TRD

    NickB_01TRD You don't need less cars, just more driveway.

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    I see you have a hot air intake there. Stock airbox is arguably better though of course not causing your issue.

    Any chance there is an air compressor or air pump on the truck? Have you owned the truck a while?
     
  7. Jan 18, 2023 at 7:31 PM
    #7
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    Not gonna deny, it sounds like the fuel pump is running to me. And if you pull the relay, which is the primary conduit that connects power to the pump if I'm reading the diagrams correctly, the pump stops running? But you still hear noise in the engine bay?

    If yes, does the engine bay noise stop after 15, 30, 45 minutes with the fuel pump relay out?
     
  8. Jan 18, 2023 at 7:47 PM
    #8
    colo4x4xj

    colo4x4xj [OP] New Member

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    When I pull the relay all noises stop except a slight, barely audible hum that is sometimes a touch louder than others. Maybe surplus power drain?
    I do run a compressor for rear bags and I cannot recall if i had this problem before or after I installed it. I just wired up my light bar again, with its wiring on the same side as the fuse box, maybe interference from that? Ive had the truck 10+ years now.
    New oem relays are awaiting me tomorrow morning, with what shify said about parts house ones they could be the culprit.
    I appreciate everybody's help on this
    Stock box worked just fine until it packed with snow and suffocated the engine...
     
  9. Jan 18, 2023 at 7:50 PM
    #9
    colo4x4xj

    colo4x4xj [OP] New Member

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    If yes, does the engine bay noise stop after 15, 30, 45 minutes with the fuel pump relay out?[/QUOTE]

    Im not sure, after watching my voltage to from 12.6 to 12.1 on a brand new battery I didnt want to keep draining it. It is ever so slight sounding
     
  10. Jan 18, 2023 at 8:27 PM
    #10
    NickB_01TRD

    NickB_01TRD You don't need less cars, just more driveway.

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    I was just wondering if theres any chance that's what's running but weird if it stops after you pull the fuel pump relay. Shouldn't be on the same circuit so that wouldn't make much sense.

    Was that with or without wheel well liners?
     
  11. Jan 19, 2023 at 7:07 AM
    #11
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    "Shouldn't be" doesn't mean "doesn't", though, and could be worth checking. :D It's a good observation.

    If the fuel pump and compressor circuit are both hot with key OFF, and both go cold with FP relay out, it would tell another story, one that's worth investigating.

    The main reason I ask this question is, and I can't imagine it being the case, but ... if the fuel pump is running constantly, I was wondering if what you're hearing in the bay is the fuel pressure built up, and sending fuel back to the pump on the return line. But that should clear within a minute or two.

    Just for shits n giggles, have you tried pulling the EFI1 fuse with the FP relay IN, and with the FP relay OUT, just to see what happens? Pretty sure your earlier model will have the EFI1 fuse. I just ask because I remember a bizarre case from summertime where someone was seeing really weird results with the FP & starter relays and pumps running when EFI1 and either of the relays are out, but don't remember the order. Let me try to dig up that post. It was such a bizarre set of symptoms to me.
     
    NickB_01TRD[QUOTED] likes this.
  12. Jan 19, 2023 at 7:08 AM
    #12
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    Here it is: https://www.tundras.com/threads/bizarre-electrical-gremlin.109383/

     
  13. Jan 19, 2023 at 7:14 AM
    #13
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    And from that post I linked, a good point is made. The ECU is responsible for sending the voltage trigger to the starter relay receptacle to trigger the relay pole to throw, opening voltage down to the pump.

    It's possible the ECU is just constantly sending that signal, and this is an ECU issue. Or it's possible something is giving the ECU an input that's telling it it's OK to trigger? Dunno, not a fan of diagnosing electrical circuits.

    In that guy's case, it looks like it was corrosion on one of the connections? If you're in the rust belt or a salt-prone area, that wouldn't surprise me.
     
  14. Jan 20, 2023 at 4:16 PM
    #14
    colo4x4xj

    colo4x4xj [OP] New Member

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    The two of my three relay replacement trifecta finally showed up today and lo and behold that was the problem. As soon as I installed the new, OEM ones the buzzing when off stopped and the vehicle fired right up on the first try. Kudos to everyone for their input and a big thank you to shifty for taking the time to send diagrams,past forums, detailed descriptions, videos, etc. These trucks are great and this almost makes me want to keep it, maybe almost haha.

    I did pull the fuse with the relay in as well as out and the pump stopped running for both.(before OEM relays)

    As far as the intake goes- I cant remember about the wheel well liners but with E rated duratracs, medium lift and ARB Saraha bar Im getting about 415 miles to a tank as long as i keep my foot out of it. Works for me for now
     
    Last edited: Jan 20, 2023
    shifty`, NickB_01TRD and w666 like this.
  15. Jan 21, 2023 at 2:35 PM
    #15
    shifty`

    shifty` I might be an adult, I'm a minor at heart

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    Damn. I'm lucky to pull 300 miles per tank!

    Glad to hear the issue is solved. Nobody ever wants to believe OEM parts make a difference. The auto parts store stuff, especially 'universal' are a crapshoot (at best).
     

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