07 F150 XL, 4.6L

Drives like a dream.

If the cruise is on, no weird noises.

If the cruise is off, and I press or depress the gas, I hear a hissing noise down by the lower left of the seat. I believe the fuel pump/fuel filter are in that general vicinity, from snooping around under the truck.

I can duplicate the sound at will. The more "pressure differential" there is, the louder the hiss is. By this I mean, if you were running a vacuum gauge, the deeper you peg the dial on the vacuum gauge the more hissing you would get. (I know vacuum gauges are old school but I don't know the correct terminology for what I'm trying to explain.)

I really don't want to take it to the dealer.

Any ideas of what I could check? The engine runs perfectly right now.

I did put a Flowmaster 40 series muffler on today so it is a bit more difficult to hear the hissing.

Thanks!

PS - This happens with or without the A/C on.

 

Do you have an aftermaket intake? Openbox intake?

 

Nope, stock intake. It has been like this since I got it about a month ago.

 

I do not have an answer but I can vouch for you though. My '07 4.6 does the exact same thing with its stock intake and magnaflow muffler. To me it sounds like it is coming from the left front area of the truck so I figured it is the air intake.

 

My hearing is a bit jacked up, so it could be coming from up front.

It is definitely on the left side though.

I wonder WTF it could be? I removed the intake and reseated it perfectly so it has no leaks.

Did you notice the new look to the intake versus the 06? I think this is where they got more horsepower for 07.

https://www.f150online.com/forums/sh...&postcount=133

 

Same truck same problem. The 08's make a similar noise but it is much more subdued. Dealer thinks it is probably just part of the design but I would quickly change that if I new the source of the noise.

Keep us posted.

 

Have talked to a few guys with the same problem and replacing the throttle body seems to fix it. I will be taking mine to the dealer soon while it is under warranty and having it done. That noise is too annoying for a new truck to have. Post back any other results.

 

My 04 has a harmonic whistle to it when temps are down around 10 degrees or lower. It's done this since I bought it. I can make it go away changing throttle position. It makes the noise at lower RPM's. I'm pretty sure it's in the throttle body. It doesn't seem to hurt performance at all, just annoying and I have read many folks with the same issue.

 

Replaced throttle body, noise has disappeared. Much more pleasant to drive.