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Discussion Starter #1
I could use a bit of help figuring out what is wrong with my car.

Car: 2007 Focus Hatchback S, Manual transmission

Problem Description:
When throttle is wide open, accelerating in second (third) gear, once I reach about 40 (60) mph, there is an air rushing noise that gets loader and loader (very similar to what I would think forced induction would sound like). At about 45 (75) mph, it feels like I have hit the rev limiter with a sudden loss of power. If I'm only on partial throttle, this will not happen and the car will rev to redline just fine. Power seems just fine at lower revs. There is no engine light.
 

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If you're in 2nd gear and going 45mph, you surely must be hitting the rev limiter. Usually it makes a stuttering noise, though, more like a jackhammer than a turbo whoosh.

Are you not redlining under those conditions?
 

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Almost sounds like some sort of induction error, like intake partially blocked.............
 

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Discussion Starter #4
.

For some reason, my original response never appeared. So let me try to repeat it, in an abridge version. Please don't take it as my being short.

If you're in 2nd gear and going 45mph, you surely must be hitting the rev limiter. Usually it makes a stuttering noise, though, more like a jackhammer than a turbo whoosh.

Are you not redlining under those conditions?
I don't have tacho, so I can't say for sure. I believe my car has MTX-75 transmission, Duratec engine with redline ~6500 rpm. Tires are 195/60R15. I calculated max speed in 2nd gear as 53 mph, which is also what I observed when not at WOT. So there is definitely something going on at 45 mph before I hit redline. In 3rd gear max speed should be 78 mph. So I guess I can get close to redline at WOT there, but it still makes the odd noise.

Almost sounds like some sort of induction error, like intake partially blocked.............
Thank you for the suggestion. I will definitely check it out. So you think it is something acting like a flap, that is cutting off air when pressure gets too high? Shouldn't that cause a CEL? I've also heard similar issue can happen if exhaust (particularly cat) can get clogged. But I have no idea how to check that easily.
 

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Doesn't the duratec have tumbler flaps in the intake runners that fail?
If so, could be that.
It also could be a pulley bearing failing on one of your accessories, causing resistance.
If you haven't changed your fuel filter and air filter ina long time, do that first, since you would need to anyway.
But, after that, I would disconnect belt and spin every pulley by hand, and, I would read up on whether or not hou have the tumbler flap problem.

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