Squeal / Whine after engine turned off

94SVTCobra

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My low mileage, completely stock 1994 Mustang Cobra (#500 of 5009) squeals / whines for a few seconds after I turn the engine off. The squeal / whine comes from under the hood and seems to be related to the fuel pump continuing to run to build pressure after engine is turned off. The squeal / whine will also occasionally occur at idle but a light tap on the throttle makes the squeal / whine go away temporarily, but as soon as the engine returns to idle it comes back. Seems to me to be related to fuel pressure so I replaced the factory fuel pressure regulator with the expensive Bosch fuel pressure regulator but the squeal / whine persists. What is that little round chrome disk/part on the return line?1655120399946.png Flow control? The whine seems to be coming from there, but this is an irreplaceable part and only included with the factory fuel lines which are only available used.
 

badass98svt

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Definitely sounds like air escaping from somewhere, by your description.
My first thought was the belt, but you say it continues to squeal after the car is shut down.
The car idles fine, obviously no fuel leaks either?
 

cobrajeff96

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That is a fuel pulsation damper. How long does the noise happen for? It's probably not a big deal.
 
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94SVTCobra

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Correct, there are no fuel leaks, and the noise happens for the entire time that the fuel pump continues to run after engine is shut down. I agree, it's probably not a big deal but was wondering if someone knew what this was, or what was causing it. Thanks
 
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94SVTCobra

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Yes, the fuel pump runs for a few seconds when I turn engine off. It also runs when I turn key from off to on position before I "crank" the engine by turning key to start position. Basically, any time that the key is in the "ON" position the fuel pump will run to maintain fuel system pressure. There must be a pressure switch somewhere that turns off the fuel pump because the fuel pump stops running after a few seconds when pressure is apparently high enough. ...I wonder if my original stock 1994 fuel pump may be less able to maintain fuel pressure and flow like it used to, or perhaps introducing air into the system which is causing it to "whine" around that pulsation damper and also run for 2-4 seconds after engine shuts down to get pressure back up high enough to satisfy the pressure switch. hmm
 

cobrajeff96

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Oh ok, I thought you mean like it runs for a good while after power is removed. What you're describing is normal operation though.

If you're concerned about the system maintaining pressure, maybe consider changing fuel filters both internal sock filter and the external one inline with the feed path.

If air were actually getting into your system, that would mean fuel would simultaneously make it out of the system. Or maybe the pump is cavitating because you have a habit of running the car aggressively with an extremely low tank of fuel. Otherwise you'd have a pretty strong fuel smell around the car and in a garage. Possibly maybe one of the purge canister lines popped off the charcoal housing or the solenoid but that's an intermittent operation and if/when it happened you'd feel a brief loss/surge of power because the intake is pulling in unmetered air.

And FWIW, all components have lifespans. It could very be the pump is on its way out and its' letting you know it somehow.
 
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94SVTCobra

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yeah, I replaced the outer canister type fuel filter, and the fuel regulator, but the tank has never been off or gone into. I am leaning toward the original fuel pump, and all of its rubber goods, being 28 years old. It may be a while before I tackle that project.
 

95opal

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Your pump should shut down the second you turn your key off. What your hearing is pressure bleed off from the pump running while the engine is off. The pump should only prime for a split second when the key is turned to the on position.
 

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