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I need help identifying this tapping/knocking sound. The sound is present from inside the car, passenger side seat area. I can't hear it outside/under the car or under the hood. Sound is loudest when in drive at idle. Sound not present while driving. Car runs fantastic. Car is a '93 LT1, 21,000 miles. I've attached an audio recording I took from inside the car. Thanks for any insight!
The tapping sound is present only when the car is stopped and in drive. If I place it into neutral, the sound is not present. I don't hear it at all when the car is in motion.
The tapping sound is present only when the car is stopped and in drive. If I place it into neutral, the sound is not present. I don't hear it at all when the car is in motion.
I would look at your motor mounts and heat shields.
I recommend getting a long screw driver or mechanics stethoscope and taking a listen to your engine. Its very rhythmic and almost in time with engine speed.
The different in engine RPM (idle versus driving or in neutral) makes me think it would be oil pressure related. Pressure is lowest at idle in drive as RPM's are lowest. Hard to tell over the internet even if I can hear it. I cannot move about the car.
Would a fuel pump ever make this type of knocking sound. The sound is very rhythmic, like 93 Rubie said. The sound is not there or undetectable above idle while in drive or reverse.
the fuel pump can be eliminated. You would clearly hear any such noise reverberating from the fuel tank. the fuel pump is a brushed motor. you would not hear a tapping. I have had a Performance external FP lock -up due to the wet magnets DE-bonded. the magnet locked up the winding core. you would hear & know. If your FP was in such a condition. This would stall the car. and will actually short-out the weakest wire contact.
Last edited by THE 383 admiral; Apr 8, 2016 at 03:17 PM.
Ok... so I've located the source of my knocking sound. It's coming from the fuel lines that come up the passenger side of the engine. I discovered this using my stethoscope. My FSM describes a knock at idle that can occur at this fuel line area. It is caused by fuel lines grounding through the plastic clip and mount that attaches to the heater housing. Has anyone experienced this?
Yes, I believe so. I think the knocking sound that I'm hearing in the fuel lines, is passing through to the hvac housing and can be heard inside the car. The FSM advises to replace the plastic insulator that secures the fuel lines to a rubber mount. My question however; why are the fuel lines making a knocking sound? Is this normal? If not, what's going on?
I have never heard this with any of my C4's I have a Aeromotive External Pump. that can produce serious pressure & volume. I could see the line tapping on the HVAC housing if the plastic clamp was loose! or the threaded stud can easily break the thin HVAC housing. I would have a 2nd hand look at the Fuel lines. to isolate if the line is tapping on the housing. then secure the feed & return as needed. In the event the clip is cracked. You could use wire cable clips. Example. Below
This is like "water hammer" in the pipes of a house.
The firing of the injectors creates pressure pulses that make a noise. That's the reason for the "pulsator" on the fuel pump (that everybody eliminates). I have heard that sometime in the '90s the pulsator was moved to a location near the fuel filter. I suggest getting one of these in-line pulsators and installing it.
Tapping/Knocking Sound
