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Old 05-05-2014, 07:13 PM   #1
Mark Ugrich
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Join Date: May 2011
Location: Auburndale,Florida
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Default hydrauliced fuel line

I'm hoping somebody here might have some ideas. On my 1984 GMC 454 3/4 ton 2WD Suburban I hear a knocking/banging noise on the center right side of the body.After checking I found the fuel line knocks in cadence with rpm and fuel pump.You can actually feel the line pulse if you hold it.I've replaced the fuel sending unit and sock all the rubber fuel lines,fuel pump with an AC Delco unit,blown out the lines with compressed air and replaced the line from the pump to the carb with braided line.Replaced the gas cap too.I'm thinking air must be entering either the main fuel line or the return line,but I don't see how.The knocking isn't there all the time it comes and goes.Has anybody seen this before?It's drivin' me nuts.Turning up the radio does help Thanks in advance, Mark
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Old 05-15-2014, 12:19 PM   #2
Mark Ugrich
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Default Re: hydrauliced fuel line

Here's an update.For the first time in I dunno 8 freakin' months we had temps in the 70's.in southeastern Wisconsin.The warmer weather seems to have helped as the noise has stopped completely.I did hear it on cold start up, but just for a few minutes.I can live with that.May be the type or brand of fuel I used.It was Shell to begin with then I used BP.I don't know if there would be a vapor pressure difference? Possibly it took that long for air trapped to work it's way through?I always thought this engine had a fuel pump with a factory return line.Turns out the engineers call it a vapor return line,to prevent vapor lock in hot environments.A/C on Etc.It's supposed to allow air to dissipate in the return line before it can get to the fuel tank and disrupt fuel pick-up.Whatever it was/is we're good for now.
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