Air Leak in Fuel System

LDD2000 on 05/05/2025 - 16:27

Hey people, so I recently bought a 2005 Hyundai Terracan, auto diesel 2.9L CRDi.

It’s had some troubles starting, after priming the fuel system using the bulb primer my car has, it seems to start very rough, then continues idling very rough. After about 5 minutes of warming the car up everything seems normal and the car drives fine.

I’ve found that the bulb primer goes soft after priming pretty much after a few seconds since priming. I did a clamp test, priming the system and then clamping the hose from the primer to the fuel tank, and the bulb primer seems to stay firm and it’s not losing any pressure. So obviously the fuel is either draining back into the fuel tank or there’s something faulty within the in-tank pump.

Just wondering if anyone has had any experience with this and what the most likely culprit is? I’ve checked the hose from the primer to tank and it seems fine and like it’s not leaking air in anywhere, and no fuel leaks either.

I’ve been told to just install an in-line check valve as close to the tank as possible and that this should fix this issue?

Let me know what you guys think.

Cheers!

Automotive Car Repairs

Comments

    • zonra on 05/05/2025 - 16:47
      +12

      Word. 20 years old Beamers be running like a dream. /s

      • SYLTB on 05/05/2025 - 20:40
        -1

        Yes, Mine is 20 y/o running like a dream.

    • Murkymerv on 05/05/2025 - 16:50
      +3

      It's a bit late for that , he needs advice not criticism . I'm surprised this later model would have a primer light ? I thought that was 70s-80 s at the latest , my first diesel was devoid of this feature….

      • Dr Phil on 06/05/2025 - 07:51

        Easy fix
        Take it to a mechanic

        This business of trying to guess whats wrong with a car is ridiculous

        Even a mechanic wont guess without examining the vehicle.

        • Euphemistic on 06/05/2025 - 10:47
          +2

          Mechanics are however known for firing the parts cannon at vehicles and atill not fixing the problem. Unfortunately mechanics have lots of time for replacing parts, and not much time for diagnosis. If you cant give them a specific thing to fix it often ends up costing a lot more than it should. Doing your own diagnosis doesnt cost anywhere near as much.

      • 2esc on 06/05/2025 - 09:48

        Be interesting to know if the newest diesels have fuel primers i know the 2015 Mitsubishi triton has one.

  • NevC on 05/05/2025 - 17:45

    Check valve may work or may not. I would just fit a new primer. Is it this type -

    https://www.aliexpress.com/item/1005006330354072.html?src=go…

    • DD2000 on 05/05/2025 - 19:52

      I was gonna replace the bulb primer as I know there known to be pretty bad. But I squeezed the primer until it was firm, and then quickly clamped the hose running from the primer to the fuel tank, and it stayed firm and didn’t seem to go soft instantly like it usually does. I’m thinking that boils it down to either a crappy hose or something to do with the in-tank pump. But I’m not too sure

      • Dr Phil on 06/05/2025 - 07:52
        -4

        Just take it to a mechanic

        • DD2000 on 06/05/2025 - 08:27
          +3

          I’d rather figure it out myself and save me a shit load of money haha, I like to learn these things anyway.

        • TilacVIP on 06/05/2025 - 08:42
          +4

          Great advice, as i'm sure he would never have figured out that was an option.

      • Euphemistic on 06/05/2025 - 09:07

        Could still be the primer return valve not working.

  • brad1-8tsi on 05/05/2025 - 17:46
    +1

    have you checked that the injectors aren't leaking down? filter housing o-ring intact and seated?

    • DD2000 on 05/05/2025 - 19:54

      I haven’t check that but I assumed it wasn’t that as after I did the clamp test as mentioned in my post, the primer stayed firm, which I’m guessing means it’s got nothing to do with anything in the engine or fuel filter but instead something with the fuel pump in the tank?

  • Protractor on 05/05/2025 - 18:02
    +1

    Does it have an in tank pump?

    Also ask your question on dedicated 4wd forum(after having a decent search there.
    What sort of injector pump do they have?
    Is there a gauze filter/banjo bolt inlet into inj pump?

    • DD2000 on 05/05/2025 - 19:56

      I’m pretty sure it has a in-tank pump? But not overly positive. But yeah that’s a good idea!

      • Protractor on 05/05/2025 - 19:59

        That should be the first cab and easy to test. BTW There used to be an online Korean place that sells Hyundai parts at good prices( Fourgreen I think, but track down the actual Korean site if it still exists.Not ebay or Amazon. If it is the tank pump I've seen aftermarket ones online go for under $200.

        • DD2000 on 05/05/2025 - 20:11

          Do you know any tests I can do to check if the tank pump is actually faulty?

          • Protractor on 05/05/2025 - 21:07

            @DD2000: That's exactly what google is for. You need info specific to your issue and car.It's out there.Invest the time, to save the time (and money). I could suggest something that 'might' work on another vehicle and it could be different to yours.

  • Tricon on 05/05/2025 - 18:23

    While not the same car, my experience were o-rings at joins. Looked fine, fuel pumped, car did not run after starting. Replaced the o-rings along the line and joy.

  • Euphemistic on 05/05/2025 - 18:45

    Sounds like one of those things where you replace stuff unfil it works properly. When my old Navara wlildnt start properly i found it was a perished primer bulb. Replaced it and there is a small leak somewhere still. After sitting overnoght it will sometimes need priming as it stalls shorlty after starting. Havent bothered tracking it down, its only really frustrating if its raining.

    • DD2000 on 05/05/2025 - 19:55

      Yeah I think I’m gonna start with placing an inline check valve close to the fuel tank and see how that goes. Don’t think it’s the bulb primer as after I did the clamp test it seemed to stay firm rather than going soft instantly like it was usually doing

  • jizmo on 05/05/2025 - 19:22
    +1

    Old navara had a crack in the line between the primer fuel filter pump to the injector pump, you couldn't see the leak as it's wrapped in thick foam. It would cough and fart and stall all the time then the next day run fine.
    Then one day it started blowing white smoke and no power, you could see the leak finally, all it took was $10 for a new hose.

  • DreadPirateRoberts on 05/05/2025 - 20:36
    +1

    Loved our old Terracan but the fuel system in the diesels were… interesting.

    Usually the injectors go first (about $400 a pop and need to be coded to the vehicle) and then the diesel fuel pump (not sure how much but expensive). Luckily, ours kept trucking along even though one of the injectors was playing up. You can get the injectors flow tested or it could be the o-rings as someone else mentioned. To be honest, ours didn't exhibit the systems you have but did blow a bit of smoke

    • DD2000 on 05/05/2025 - 21:28
      +1

      I’m pretty sure it’s nothing to do with the injectors as after the hose clamp test I did as I mentioned in the post, points to an issue either in the hose leading to the fuel tank or something faulty with the intank pump. But yeah it doesn’t blow any smoke or anything, runs rough on cold start after priming for about 3 minutes and then it’s like everything quiets down and runs smoothly, almost like all the air has been purged out and is fine idk

      • Protractor on 05/05/2025 - 22:29

        My gut feeling is supply, not injectors.Possible air in the feed line, or pump.

  • JimB on 06/05/2025 - 15:15

    20yo car with not much value.

    I'd be starting the car 5 minutes before you need to drive to 'fix' the problem.

    • DD2000 on 06/05/2025 - 16:46

      The thing is I’ve got to prime it every single time and it’s a pain the ass haha, I’d rather just figure out the issue myself and get it fixed rather than having to do that every time I wanna drive the car

      • JimB on 06/05/2025 - 17:19

        What is this priming thing you are referring to? lol

        • DD2000 on 08/05/2025 - 15:04

          It’s a manual bulb primer, you squeeze/pump it a few times to pressurise the fuel system or purge air out of the system. I have to do that every time to start it.

          • JimB on 08/05/2025 - 15:15

            @DD2000: Did it come from the factory with a bulb primer?

            Amazing that a modern car (well built in 2005) would have/require such a device?

            Like hand cranked windows these days.

            • DD2000 on 08/05/2025 - 20:19

              @JimB: Yeah it is factory installed, I find it quite handy tbh, if I didn’t have this primer I wouldn’t be able to drive anywhere at the moment.

          • tenpercent on 08/05/2025 - 15:21

            @DD2000:

            I have to do that every time to start it.

            Like this?

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