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Go Back   Hummer Forums by Elcova > Hummer H1 Discussion Forums > Technical Discussion and Customizing your H1

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  #1  
Old 01-20-2007, 06:08 PM
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leenigen leenigen is offline
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Default Whats this sound?

Well it looks like they won't let me attach a wave file so I'll try to describe it.

A fraction of a second before I start the engine and for a second after I shut it off (only when still cold) there is a fast knocking sound from behind the dash/firewall. Its comming from the area of the lift pump I think but I can't find it. Whatever this noise is, the truck always made the sound when I just shut it off after running only for a few seconds. After changing my cold start advace switch it now makes the noise quite loudly for about 5 minutes before going away. I'm not too concerned but new noises do make me a bet nervous.
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Old 01-20-2007, 07:36 PM
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Default Re: Whats this sound?

Sounds like its probably the lift pump itself. If it is noiser then it used to be its probably begining to fail.
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Old 01-21-2007, 04:38 AM
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Default Re: Whats this sound?

Quote:
Originally Posted by leenigen
Well it looks like they won't let me attach a wave file so I'll try to describe it.

A fraction of a second before I start the engine and for a second after I shut it off (only when still cold) there is a fast knocking sound from behind the dash/firewall. Its comming from the area of the lift pump I think but I can't find it. Whatever this noise is, the truck always made the sound when I just shut it off after running only for a few seconds. After changing my cold start advace switch it now makes the noise quite loudly for about 5 minutes before going away. I'm not too concerned but new noises do make me a bet nervous.
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Old 05-28-2007, 02:53 AM
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Default Re: Whats this sound?

Get an Ohm meter (DVOM) and read the cold start solenoid for resistance. Check for volts DC and Amperage. You should have enough Amps to drive the solenoid. The light load advance does nothing but advance the fuel sooner and stops advancing as soon as you apply pressure on the fuel pedal. If it didn't you would have one heck of a loud knocking noise.
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Old 06-02-2007, 03:01 PM
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Default Re: Whats this sound?

Lift pump, When noise is no longer there your gonna need A new one. Should hear it run with key on for maybe A minute and when key is off it will run for maybe 2-5 sec. Just open the hood and hold the pump while someone turns the key on and you can tell. You can check lift pump pressure if you have A gauge, or inside the drivers side front wheel well you will find A valve right at the firewall for draining water from the fuel bowl, simply open the valve and turn the key on, if fuel spills lift pump is operating.
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Old 06-04-2007, 05:18 PM
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Default Re: Whats this sound?

Yeah, it was the lift pump. I changed it a few weeks ago and everythings been fine since.
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