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Fuel Pump Replacement

Discussion in '80-Series Tech' started by 410225, Oct 20, 2003.

  1. 410225

    410225

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    issue and it comes directly from the center of rear seat where the fuel pump is located. Whenever I drive over 65mph, the humm starts and gets louder faster the speed. Checked outside to hear any noise, no.
    How hard is it to replace the fuel pump? Any of you had this experience before? I have 97LC with 112k mi.
     
  2. Gumby

    Gumby Supamod Staff Member s-Moderator

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    Fuel pump is not going in increase in volume with speed. IFAIK, the 97 uses a constant supply pump with a return rather than the duty cycle pump now being found on some makes.
    The fuel pump is also going to hum even if it's new. Obviously, I can't hear yours and maybe it is too loud.
    The labor book calls for 1.8 hours of labor. It's much easier than changing one on an American car as there is an access plate under the seat. No need to pull the tank.
     
  3. Kyle

    Kyle

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    Not sure exactly how bad your pump is but i know with my car as I run lower on fuel, more of the pump is exposed (inside the tank) and when I'm really on E, everyone in the car knows it. (Of course it is an aftermarket warlboro 255lph, or as some affectionately call it "whineboro").
     
  4. 410225

    410225

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    Thanks Gumby for your reply. I always thought it is someting else and I hope it is but, I know it comes from the center of the vehicle where the fuel pump is located. it is loud when I am driving 70mph. What else could be the issue? I don't want to bring to stealer to pay $70 to just check on it.
    Thanks for your help.
     
  5. DanKunz

    DanKunz SILVER Star

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    soounds like driveline whine to me...increasing with speed..etc

    You may also be hitting a resonance with some metal component and getting some cool noises.

    Hard to say without hearing it.
     
  6. 410225

    410225

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    DanKunz,

    How is your resonator+tailpipe attached to the body? It looks like my 97LC has a rubber padding and it just floats over a bracket. I could move it around with my fingers. Is this normal? Maybe that's what vibrating? I am getting so frustrated I am in a verge to just take it to stealer and have them fix it whatever it is.
    If it is a driveline, what do I need to look at?
    Thanks for your help.
     
  7. cruiserman

    cruiserman

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    The resiliant mount may be broken. Easy to replace if you haven't hammered the exhaust pipe out of alignment (ask me how I know ::)). There are 3 mounts on my '93.
     
  8. IdahoDoug

    IdahoDoug

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    Dark,

    Before doing anything expensive, lube the driveshafts properly and check the gear oil level and condition in all three diffs. By far these are the highest likelihood of fixing a drivetrain hum.

    Doug
     
  9. Beowulf

    Beowulf

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    and lube the spiders.
    -B-
     
  10. 410225

    410225

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    Well, I did check the fuilds. All clear and full. Checked and greased spiders. Checked the resistance in Fuel Filter. Normal.
    Now my only hope is the exhaust somehow vibrating against something. As I mentioned, my tailpipe is free loose and it seems just hanging on the L-shaped bracket. If I lift and move it around, it moves. Is this Normal? What is the resilliant hanger or mount?? ??? :(
     
  11. IdahoDoug

    IdahoDoug

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    I'm not there to see the movement and feel the pressure required to generate it, but if the mount's intact and the pipe's not cracked or leaking then you're not likely to find a hum in the exhaust. Does the humming seem speed related, or RPM related?

    At 70, tromp the throttle and at the different engine RPM did the hum change?
    Ditto, but let off the gas - hum change?
    Go 80, put it in neutral and coast down to 60, then put it back into Drive. Did the hum progress down with vehicle speed?

    If your spiders/shafts are greased, then I'd speculate a tire issue, followed by a rear wheel bearing. The rear bearings are often ignored as few realize the 80 has it as part of the HD full floater rear end. How many miles on your rig and what's the service history there? As to tires, there will be no visual clues to them being the problem, but you can swap them front to rear to see if anything changes. Tires would be the next guess.

    One wild guess from years of wheeling would be to examine your exhaust tip. If it's been distorted, or has an edge ground a bit from offroading or dragging against a curb, this can make a lot of noise at speed. If so, make the opening round and file off any rough edge. I've seen two identicall brand new cars go by the DOT's audio meters to pass the drive by noise requirement. One did not make it because the tools cutting the exhuast tip were dull that day. A few hits with a file and it was able to pass.

    Doug
     
  12. 410225

    410225

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    Hey Idahodog,

    Thanks for the info. I really appreciate it.
    I am going to check and rotate the wheels next. Also, I am going to check on the exhaust tip and I have noticed, it is angle cut but top section has another cut across the tip. I wonder why.
    When I am driving my 97LC w/112k mi, I hear the hum starting at 65mph and up. When I am coasting 70mph, hum gets louder. When I let the foot of the pedal, sound goes away. It is more speed related than rpm.
     
  13. IdahoDoug

    IdahoDoug

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    Help me out with that description:

    Coasting @70mph means no foot on the gas in my world. But you write "coasting at 70 hum gets louder" and "let foot off pedal sound goes away". Can't figure out what you're doing here.

    Doug
     
  14. 410225

    410225

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    I meant cruising 70mph with my foot on accelerator pedal depressing and giving gas.