A coupe of years ago I replaced the original fuel lines with steel brake lines. It is a '72 with original FI and fuel pump relocated to the front by PO. I used a right angle fitting at the firewall rather than bend the line. On driving, the fuel lines buzz with a harmonic at all speeds that isn't nearly as prominent when not moving. I have covered the exposed lines with old rubber lines and secured them pretty well but no effect on a still noticeable buzz.

I am replacing the fuel lines now in a '76 and have steel lines long enough to bend.

If the harmonic buzz in the '72 is from cavitation at the right angle joint when there is significant fuel flow, then this should not occur with the '76. (I recognize that there is fuel circulation even at idle, but I don't get near as much harmonic buzz at idle. And it'a a much higher buzz than I would expect from road vibration.)

In the future I'll really tie those suckers down in the engine bay and where ever I can reach in the tunnel in the '72 to see if that helps or replace them with longer ones like the '76 if that is successful.

Has anyone had this problem or any ideas to offer?

Possibly coat them in bedliner? We haven't done this yet, I suppose it depends on the size of the tunnel holes. If not that maybe heat shrink tubing?

I just replaced my old fuel lines with SS as well. I don't have the car running yet, so no noises for me, but there are metal clips that hold the old lines in the tunnel. It was a bit of a pain to get the new ones in the clips, but it may hold them more securely and prevent vibrations from rattling the lines. also check the grommets where the lines enter/exit the tunnel.

When you pull the old lines off, check them. There have been reports of ethanol eating the liners in SS fuel lines, but you can't see the cracking because of the braid.

Zach

When I replaced my lines with SS, I got some 8mm heat shrink tubing in 20 foot lengths from harbor freight. I coated the tubing and then shrunk it in place. No noise so far and the tubing was inexpensive..... And they carry the stuff in green, black and yellow colors.

Harmonics (overlapping nodes on the harmonic scale) are vibration induced and destructive. That being said, I doubt very seriously that is what you are experiencing. I think one of the old metal clips is in contact with the line. Remove the 3 bolts holding the shifter in place then rotate the base of the shifter 90 degrees to expose the tunnel and the lines. Push the lines towards the pass side a few inches and see if it goes away. I don't believe that the fuel passes thru the line fast enough to cause turbidity or cavitation problems, either.

I might suggest that it could be the fuel pump mounting.
If that is done improperly, it turns the car into a speaker for the vibration to amplify.

Did that in the 911, but some rubber wrapped around the pump so the metal clamp did not touch the pump was all it took to stop the noise.

my 914 has the pump mounted up front on rubber isolators for the bracket to body connection, and rubber wrapped on the body of the pump at the pump to bracket connection.

It took all that to make the noise stop in both cars.


Rich

Thanks everybody. I would describe the sound more as a hum than a buzz now that I think about it more. The pump is isolated from the steel lines by rubber FI hose but it may well be the pump inducing the fuel vibration instead of the fuel movement itself.

In any case I'll move things around in the tunnel and the rubber around the pump is a good idea too. Glad to hear someone else has had and solved this PITA. It was nice and quiet with the old plastic lines and then I went and upgraded things!

BTW for the next guy to upgrade the fuel lines, don't mess with right angle joints. Matching all the connections at a parts store was a chore. Most stores have a limited supply of these brass fittings and you end up with oddball combinations to get one line joined to the right angle fitting and that joined to the other line. Get a 6+ foot line,,,it'll bend easily. Or cheat and get the pre-bent lines and save the hassle.

I'm originally from Nebraska.

The corn hole state and Iowa have had ethanol since the mid to late 70's.

The only problem I've ever seen in regards to ethanol is that it was really, and I mean really, effective, at cleaning the fuel system and lead out of the carb/tank/lines

Today's fuel lines have multiple barriers to reduce emissions. For example, today's plastic fuel lines have 7 layers of different plastics, with different characteristics to keep the California emissions people from getting their panties in a bunch.

And yes, I have worked for a company that made fuel and brake lines.

Zach.