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  1. #1
    Member kiev's Avatar
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    What is this sound?

    Car drives otherwise normally. Fuel pumps were put in new, 4 years/10k miles ago. Sound best heared by the rear left wheel. If it matters, every time I open my fuel cap it sound like I've opened a bottle of mineral water with gas


    https://youtu.be/crqevEEgOLk

  2. #2
    .036 Hoonigan™
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    Re: What is this sound?

    Sounds like noisy fuel pumps to me. What brand pumps were installed 4 years ago? I'd be surprised if Genuine Bosch pumps sounded like this in 4 years, but if they were any aftermarket brand...

    When removing the fuel cap after driving for a while, you may notice pressure escaping. This is normal. The 124 fuel tanks are pressurized.

    Dave M.
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  3. #3
    Member kiev's Avatar
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    Re: What is this sound?

    They were Bosch. Never hear this sound before. Definitely new. So this means the fuel pump is on a borrowed time?

  4. #4
    .036 Hoonigan™
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    Re: What is this sound?

    Quote Originally Posted by kiev View Post
    They were Bosch. Never hear this sound before. Definitely new. So this means the fuel pump is on a borrowed time?
    It's possible they are on borrowed time, yes. But they could also last years - if you don't mind the noise. You can confirm the noise by removing the cover below the pumps and verifying that's the source.

    To narrow it down further you can remove 1 wire from each pump, then apply +12v directly to the pump terminals (with ignition off!) and listen to each pump separately. Usually, you can hear the difference if only 1 pump is noisy. I'm still shocked that a Bosch pump would have this type of noise in such a short time. Did you buy from an authorized dealer?

    EDIT: I can't tell in the video exactly how loud the noise is, so I'm not certain if the noise level is higher than normal / new pumps. However you can clearly hear the pumps are not remaining on consistently, there is a hiccup which should not be present. I'd pull the rear seat cushion and put your hand on the fuel pump relay. See if you can feel a click that coincides with the audible hiccup. If so, it could be the LH module. If not, the pumps are suspect.


  5. #5
    Member kiev's Avatar
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    Re: What is this sound?

    *It's definitely loud. Can hear them from the driver's door, when exiting, with car idling. Just drove a couple of miles - I've got full power.

    *They were put in by a Merc/Bmw shop back in Los Angeles, that was reputable and had always huge line of people. But then, everything was over-packed/over-capacity in that cursed "city of Angeles". I remember asking owner whether they put MB part or Bosch and he did tell me it was Bosch.

    *Once in a blue moon, after re-starting warm car, I get swirling/gargling noise, as if something, kinda, about to seize or churn through something. This sound is the from the back, where fuel tank/fuel pumps are. It's not a metal to metal sound though. It goes away with in seconds. I may be mistaken, but it tends to happen if I add injector cleaner (techron, gumout, etc). Weird Fuel filter was changed at the same time with fuel pumps

    * Definitely nothing is clicking from under the back seat. I've read here about that being related to a bad LH module


    This is how my car sounds: https://youtu.be/Y5EjWLZc890?t=52



    Thanks, Dave!

  6. #6
    .036 Hoonigan™
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    Re: What is this sound?

    I listened to the brand-new pumps in my wife's E420 for comparison. They are not quiet, and definitely nowhere near silent as that video almost makes them seem. But the "bad" pumps in the "Old Noisy Pumps" video did sound louder than normal. Volume is very subjective so it's difficult to say what's good or bad. I've had several fuel pump failures on several different cars. The 2 typical failure modes I've personally experienced are:

    1) One pump intermittently turns off, drastically reducing engine power, with zero fault codes or any other symptoms. It was finally diagnosed using a remote fuel pressure gauge visible while driving, where the pressure dropped to 1/3 of normal when the power loss occurred. This particular pump was otherwise quiet and seemed fine.

    2) I've had some pumps sound like they were full of rocks. I mean nasty, horrible, grinding noises. They still pumped fuel at normal pressure, but I replaced them ASAP. These were typically old, original pumps with high miles and beyond their normal service life.


    If the pumps are just slightly louder than normal, but otherwise working ok, I'd be tempted to leave them alone until something gets worse. As mentioned in my previous post, the "hiccup" in your video isn't normal - something isn't right, but I don't know for certain if it's the pumps, or the electrical circuit feeding the pumps (LH module / relay / wiring).


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    Re: What is this sound?

    i'll leave them alone for now, as neither 1) or 2) applies, but will monitor for now. Curious if the noise and occasional swirling/churning noise might be related to my dyno power curve being non-smooth. Over 4.5 years I've dealt with about 6-7 indy mechanics. No one was even remotely interested in engaging with the car/troubleshooting/preventive maintenance. Change this part - no problem, change that part - no problem. Otherwise no additional input/suggestions/tinkering. No matter how hard i tried or spent with them. I'm starting to think I look like a 19 year old student with a bus pass....

  9. #8
    .036 Hoonigan™
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    Re: What is this sound?

    Oh yeah, I forgot to mention the gurgling / swirling / churning noise. One of my cars (1994 E420) has this intermittently, usually after a cold start. It took me years to pin down the source, becaue the noise never lasted more than a few seconds, and could not be reproduced on demand. One day I happened to have my head in the trunk when the engine was started, and could clearly hear the noise was coming from inside the fuel tank - probably related to the lower fuel bowl in the middle around the pickup & return. Fuel level didn't affect anything. It's still intermittent, and IIRC new pumps didn't cure it either (although, I can't recall if I've heard the noise since the new pumps were installed). I've never heard this noise on ANY other 124. There were no problems or symptoms besides the noise, btw... normal power, economy, etc.

    BTW, to rule out fuel pressure as any possible cause for the dyno power dip, you can add the remote fuel pressure gauge temporarily and drive (or re-dyno) while watching fuel pressure. I really, really doubt that odd-shape dyno curve would be in any way related to fuel pressure; especially since it didn't affect peak power.


  10. #9
    E500E Guru sheward's Avatar
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    Re: What is this sound?

    I have heard this gurgling noise on occasion as well.

    drew
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