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Consistent knocking?

Discussion in 'Suzuki Carry' started by ApoX, Jun 5, 2016.

  1. ApoX

    ApoX New Member

    so while sitting in my truck with the windows up a week ago I noticed this knocking sound, it's fairly faint and is always always At a consistent Rhythm. Meaning if the truck is idling, in or out of gear, or while accelerating or decelerating (although it's hard to hear then) it's the same sound. It can be heard in the cab or towards the back of the truck, but not the front or under the truck near the engine. Being that it doesn't correlate with RPM I doubt it's engine related but it just doesn't let up, and I'm just very curious what it could be. Any ideas?
     
  2. ApoX

    ApoX New Member

    when I say rhythm I mean more tempo, its perfectly on time about .75 of a second apart every time.
     
  3. ApoX

    ApoX New Member

    I think I may have narrowed it down. I can actually feel the thumping with my hand on the gas tank and it's loudest around that area. Fuel pump?
     
    Last edited: Jun 5, 2016
  4. fmartin_gila

    fmartin_gila Active Member

    A jerk type fuel pump will have a "thump" which may or may not be noticeable. A rotary pump will not have the "thump". I may be mistaken as I have not been into the fuel pumps but I was under the impression that the in-tank pumps were the rotary type. You might do some sleuthing around the tank & lines and find that someone has added a jerk type pump somewhere in the fuel line near the pump. Electric pumps are better at pushing fuel whereas engine mounted mechanical pumps are good at sucking fuel so if someone has mounted an aftermarket electric pump it should be near the tank. This is kind of standard as the in-tank pumps are very expensive.

    Fred
     
  5. ApoX

    ApoX New Member

    I posted a video of the sound. You can hear it over the engine if you listen for it. I start at the back, and work my way to the cab with the doors closed.

    https://vid.me/2Iq4
     
    Last edited: Jun 5, 2016
  6. fmartin_gila

    fmartin_gila Active Member

    That doesn't sound like an aftermarket fuel pump. More like a crankshaft knock put not positive. If you can beg, borrow, or buy a mechanics Stethoscope you can pinpoint exactly where its coming from.

    Fred
     
  7. ApoX

    ApoX New Member

    Its always at the same tempo though, the crankshaft speed would change with RPM, and I can feel the thump with my hand on the gas tank at the back of the truck. I'm more of a motorcycle guy so I don't know for sure, but it would seem odd I could feel the thump of a crankshaft in the gas tank. I don't even feel it on the truck chassis. It's in the shop right now for the frame work, so I'll look into it further when I've got it back on Wednesday.
     
  8. fmartin_gila

    fmartin_gila Active Member

    You are right if crankshaft or any other engine related matter, it would change tempo with RPM. Thinking on it a bit if it was a jerk type fuel pump, the tempo would increase as you raised RPM too as it would be using more fuel to run at a higher RPM. Your choice depending on your tolerance and how you feel about it whether to just drive it or maybe drop the tank when you get it back to see if you can locate it.

    I've been pulling wrenches for better than 60 years now and I've seen & heard some mighty weird things from different vehicles over the years.

    Fred
     
  9. ApoX

    ApoX New Member

    pretty sure ill be picking it up tomorrow, I just realized, I don't think I heard it when the tank was full or when I first got it I drove it home basically empty and either I was too excited to notice it, or it wasn't making the noise. Its at a half tank right now and I definitely hear it. Once I get it home I'm going to go fill the tank and see if the noise goes away.
     
  10. ApoX

    ApoX New Member

    Solved! Well only if you can tell me what this is, pretty sure it's s fuel pump of sorts.

    image.jpeg It has a nice little thump to it if you put your hand on it, below is a video of this alien technology pulsating... Lol

    https://vid.me/yEZA

    Look carefully at the base of it
     
  11. fmartin_gila

    fmartin_gila Active Member

    That certainly is a fuel pump. Guess it was all for nothing. Man next door has one like yours and each day when he starts it you can hear the pump pulsing in my house. His must lose the prime or his carb leaks down or something as he lets it pump for about 3 or 4 minutes till he hits the starter, then it starts instantly.

    I was also under the impression for some reason that the pump was in-tank integral with the sender but that looks original so I was wrong on that.

    Fred
     
  12. Ronin

    Ronin Active Member

    Yep, mine sounds the same. No worries.
     

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