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Discussion Starter #1
I just noticed that my car started doing this since the weather has warmed up a bit...

Here are some basics:
4.6, 4R70W each with 106,205 miles
Sparkplugs have some decent mileage on them (At least 25k miles..)
Older Fuel Filter (about two years)
87 Octane Gas
Motorcraft Synthetic Blend 5w20 with 2,700 miles since last oil change.


At about 35 MPH, my car sits right in Overdrive. With a slight press of the gas pedal the transmission goes to downshift to 3rd, and I get this slight clanking noise that can only be heard with the windows down. It isn't an engine knock, it isn't a tick, but it sounds like there is a tiny tiny faint diesel underneath my car for a split second.

It happens as well sometimes when leaving a stoplight if I give the pedal a moderate push. Not a soft take off or a launch, but just a moderately hard push.

It also happens at around 50 when in O/D; if I press down the pedal, the tranny won't downshift but I get the noise again there as well.

You guys know that point with an Automatic Tranny where you give the engine gas and the engine bogs for a split second before the tranny downshifts...it happens right there. Just in that bogging period.

NOW, because I've been experiencing this, I decided to take the car to some back roads and jump on it really hard about 5 times. The engine pulled super hard and I didn't get the noise a single time. Everything felt and sounded freaking perfect when it was under hard acceleration. It seems like it only comes if i'm giving the accelerator moderate pressure and the car is about to downshift from O/D to 3rd, or in the highway cruising case, right around 50 when I give the engine a little gas during that bogging period before your RPM's jump.

I tried to catch it on video, but the noise is so freakin faint your gonna have to reeeeeeally have your volume up on some high quality speakers to hear it. You also can only hear it with the windows down so that's why I had to have them down during recording.

It's nothing that is super noticeable and the car isn't driving or behaving differently, but I'm reeeeally stumped as to what this is and it's worrying me (leaving on a 2,000 mile road trip a week from today).

Any ideas?


 

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Discussion Starter #3
See that's what I mean, it's sooo damn faint.

Only when driving in that bog period before a downshift or when giving it a little extra gas.
 

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9k All Day.
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nope, dont hear a thing.
sorry noco. :/
 

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Discussion Starter #5
I really think it has something to do with the fuel...I had been running 91 and swapped down to 87 because I was 99% sure the car had never been tuned. I may try and see if next fill up running 91 doesn't fix it. I dunno, I'm just confused...
 

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Discussion Starter #6
Anyone...?

I just drove for like 15 minutes and it only did it twice, while I was purposely trying to re-create the sound. I'm so damn confused...
 

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King Trashmouth
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21,891 Posts
Well the scenarios that you described of high load and lower RPM are typically where detonation occurs, especially on mild vehicles. Not to mention the "diesel" sound is basically what is happening, diesels are essentially detonating all the time.

But the good news is I can't discern it in the videos. Could be crappy audio, but I can't say for sure. Usually you can hear detonation without having your windows open, it's very distinct. Usually if you have to ask "is that detonation?" it isn't. If it is detonation, it's more like "Oh ****!"

Also detonation doesn't happen all the time. It would only happen in those scenarios of high load low RPM. If you can effectively avoid being in that location on the power curve, you can avoid detonation without changing anything else. If it turns out it is happening (which I'm skeptical of) just downshift.
 

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well not for nothin but im just gonna throw this out there it could be a wrist pin or somethin else in the lower end,ya can try startin your car up and just feather the gas pedal a few times to see if it does it,hopefully im wrong,i hate bein the negative one been but just thought i should mention it.
 

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could be preignition?
 

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MMM JELLO!!!
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maybe its the gasket between the engine n exhaust manifold. thats what it did in my v6 in the driver side and changed it and it was all good.
 
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