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Discussion Starter · #1 · (Edited)
Hi All -

I recently changed my oil and filter, and washed my aFe dropin filter with 2 days time to dry - things I've done plenty of times before. I rechecked my work and am unable to figure out why my engine/car sounds different when I turn the engine off.

The car starts up normally, seems to run normally, check engine light stays off. However when I shutoff the car, there is a shake and pressure release sound that happens (2 videos of this below). Not sure if its just in my head, car seems to be a bit down on power under normal driving.



Any clues on what I should look for/what this could be?

Much appreciated in advance.
 

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Well, your videos didn’t make it through due to privacy settings within Vimeo.
 

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I heard it, but I don’t know what the cause is. We need some more troops to check-in here. Let’s ping Grimbrand, Dino, and 5LHO
 

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Discussion Starter · #5 ·
I heard it, but I don’t know what the cause is. We need some more troops to check-in here.
Much appreciated. I thought that perhaps the intake clamps came lose while I was taking the air filter out and cleaning the airbox, but it looks good.
 

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While I haven't driven around in one of these before, it's very common for an engine (on shutoff) to shudder as ignition is turned off, and then the last compression stroke will typically bleed down, giving kind of a 'chuff' noise (blowing through into the intake or partially opened exhaust). It's not as noticeable on some engines as it is on others. None of that concerns me too much - but the fact that it only recently started doing it on your car does.

Honestly the only thing that comes to mind (that could be a real problem) is a leaky intake valve - carbon buildup on the direct injection engines can sometimes cause problems, but this one would be odd. I don't really think that's likely to express itself this way, but it's possible. If it was a problem with ring seal, and we're hearing leakdown go shooting into the crankcase, I think we'd get more smoke coming out somewhere.

Lastly, and this isn't a "problem" technically - it could be the air conditioner compressor 'hissing' in much the same way as the engine's compression stroke would.

If it's significantly different from your car's original behavior, maybe take it to the dealer and have 'em take a look.
 

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Discussion Starter · #7 ·
While I haven't driven around in one of these before, it's very common for an engine (on shutoff) to shudder as ignition is turned off, and then the last compression stroke will typically bleed down, giving kind of a 'chuff' noise (blowing through into the intake or partially opened exhaust). It's not as noticeable on some engines as it is on others. None of that concerns me too much - but the fact that it only recently started doing it on your car does.

Honestly the only thing that comes to mind (that could be a real problem) is a leaky intake valve - carbon buildup on the direct injection engines can sometimes cause problems, but this one would be odd. I don't really think that's likely to express itself this way, but it's possible. If it was a problem with ring seal, and we're hearing leakdown go shooting into the crankcase, I think we'd get more smoke coming out somewhere.

Lastly, and this isn't a "problem" technically - it could be the air conditioner compressor 'hissing' in much the same way as the engine's compression stroke would.

If it's significantly different from your car's original behavior, maybe take it to the dealer and have 'em take a look.
Thanks for your reply. The AC was off - before and during filming the video, the car has 55k miles.

Yes the behavior of the car during shutoff is different than before.
 

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Thanks for your reply. The AC was off - before and during filming the video, the car has 55k miles.

Yes the behavior of the car during shutoff is different than before.
Since it is easily reproducible I would try and pinpoint where that popping sound is coming from. Then you might have a chance at finding the cause. Is it coming from the top of the engine or bottom? Left or right side?
 

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Hi All -

I recently changed my oil and filter, and washed my aFe dropin filter with 2 days time to dry - things I've done plenty of times before. I rechecked my work and am unable to figure out why my engine/car sounds different when I turn the engine off.

The car starts up normally, seems to run normally, check engine light stays off. However when I shutoff the car, there is a shake and pressure release sound that happens (2 videos of this below). Not sure if its just in my head, car seems to be a bit down on power under normal driving.



Any clues on what I should look for/what this could be?

Much appreciated in advance.
A slight shudder when you switch the engine off is normal but that "poof" sound is as if a valve is opening to release pressure. The EVAP canister purge valve is mounted inside the driver's side strut tower on my GT. I don't know if it's in the same location on your car but I suspect that could be the culprit. You could put your ear next to it while the engine's running and ask someone else to shut the engine off to find out if that's where the noise is coming from.
 

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Mine does the sound too. Just never noticed it until a few years ago, the same question was asked by a Forum Member, maybe from another Mustang Forum. I believe all the 3.7L v6's do it :)

I park my Mustang. The radio is on and I turn off the engine. The radio is still on and doesn't go off until I open the door. By that time the sound has already happened and I don't hear it because the radio is on until I open the door. If I have the radio off and turn off my engine and listen for the sound, I'll hear it :)
 

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There's a bunch of things I can think of that could do that. Everything from a leaky brake vac hose, to canister purge valve, to a cracked intake manifold. Without more than a couple vids and no diag, I'd be hesitant to draw a conclusion. I would recheck your work on the intake stuff, though, first a squirt bottle full of water with a little of dish soap may help you pin-point leaks without damaging anything.
 
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