Knocking Sound Fuel Lines

[MitchV]

My '93 LT1 has knocking sound that is coming from both of the fuel lines that route up the passenger side of the engine. I can hear it faintly inside the car (passenger side). I pinpointed the knocking in the fuel lines using my stethoscope. It's a rhythmic sound that is present at idle in netural and in drive/reverse at idle. I do not hear it at all when driving. Any idea what the knocking might be? Pulsing from the injectors?

 

[Tuna]

Here's something I found posted by Hib a few years ago here in the forums about something called 'fuel line hammer':

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Fuel line hammer sounds like someone lightly "thunking" the bottom of a small tin can. It is more obvious from inside the car, especially on the passenger side, than it is on the outside.

The noise typically would go away after warm-up though it might change a bit.

The noise comes from the abrupt pressure fluctuations inside the fuel system caused by the injectors opening and closing. In MY93-94, GM made some changes to the fuel system and fuel line mountings to mitigate the problem.
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My ex '92 had this and I replaced the fuel line mounts with newer pieces for the '94 and later cars. Seemed to help.
The later fuel line mounts had more flexibility than the '92 and early '93 mounts.

 

[MitchV]

Tuna, I think you got it. Is the knocking a real concern or just a sound that bugs me at idle?

 

[Tuna]

Tuna, I think you got it. Is the knocking a real concern or just a sound that bugs me at idle?

I was told that is was just an annoyance but I changed out the fuel line mounts under the hood anyway.
Put CORSA exhaust on it and you'll never hear this noise again.

 

[MitchV]

Thanks for the info Tuna- I'll look into changing out the mounts.