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Fuel line knocking noise

Frank68

Frank68

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I recently changed the fuel pump in my 68 Charger R/T. For the past couple of days, I've noticed a knocking noise coming from under the car (passenger side), that would begin when I put the car into Drive. Reving the engine would make knocking faster for a couple of seconds, and then it goes away. Once, I let off the accelerator, it's back. I traced the noise with a stethoscope and the origin seems to be where the line goes into the fuel tank. That's where it is the loudest, and where it ends. Has anyone here experienced this?
 
Actuating rod worn too short&clanging on f.pump arm? Bad pump? Think I've read of this but never experienced.
 
I once had a customer who thought he had a connecting rod knocking. I removed the fuel pump bolts and let the pump hang there on the lines. Started it up and the noise was gone. Bad pump. On a Chrysler product it could also be a worn pushrod.
 
The knocking noise is not in the engine compartment. Engine compartment has no odd noises. It is strictly coming from line as it goes into the fuel tank (where the sending unit goes in). Can it still be a bad connecting rod?
 
"Push rod" for the fuel pump, not connecting rod.

You are talking about a mechanical pump on the engine?

Why did you replace it?
 
If you recently change the fuel pump, I suspect it is the fuel pump itself. I had one do the same thing. I guess I didn't hear it back at the tank but what mine ended up being was the spring on the actuator arm on the fuel pump wasn't strong enough to keep tension on the arm as the cam pushed it up and down. It sounded like a rod knocking. I suspect you are hearing the rattle from it traveling through the fuel line. Is your fuel line metal all the way back from the pump to the tank? It could also be as Khryslerkid mentioned. a worn push rod but I'm guessing it is the pump since you recently changed it and didn't notice the knock before.
 
I changed the fuel pump because it was leaking both oil and fuel. I'll take it back off and check for tension in the arm. And I meant to say push rod. haha. When I checked with my stethoscope, the noise was non-existent near or around the fuel pump, which is why I am completely confused. It starts from behind the passenger rear wheel, and works louder as it reaches the fuel tank. But, I'll check the pump.
 
You can remove the pushrod plug and check through there without removing the pump...
Also sounds like the line might be making contact on the frame, exhaust bracket or something else? Just a thought.
 
Last edited:
Checked the pump it looked fine. Turned the car on, noise from rear of the car is still there. Took the car out for about an hour drive, no issues. Thoughts?
 
another baffling gremlin. If the noise is coming from the gas tank area, do you think it could be an exhaust pipe or the fuel line causing the noise? It sounds like you only have it at idle. Doesn't make sense that it only showed up after changing the fuel pump.
 
if it speeds up and only happens in drive then i would check for a small crack in the exhaust.pipes move slightly under toque and speed up with rpm.
 
If you want to eliminate the fuel pump, disconnect the inlet to the pump, put a rubber line into a gas can, and see if it still does it. If it does, it's in the pump area. If it doesn't, it could be a part of the fuel line vibrating against something else. I would check this first.
 
Yeah, I'm betting on an exhaust pipe or fuel line that's hitting the frame or body of the car. Wherever a line goes through the frame, you can wrap it in a piece of rubber (bicycle inner tube or anything handy... piece of hose or ?) You have to look close & need the suspension at ride height. Maybe you can find a shop with a lift where the car is lifted by the tires (not frame) and take a look?
 
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