Guys, 2003 F150 4.6 with 102,000 miles. Upon first start-up in the morning, The truck starts and has a "MOAN" coming from under the hood. I found that when I loosen the strap that holds the air filter box together-- The "MOAN" gets REAL loud..When the motor runs for about one minute-- the sound goes away.. What can cause this noise and how do I get rid of it??

 

I have seen posts about the 5.4 motors but nothing about 4.6 motors.. Anybody have ideas???

 

most common ford moan is the power steering pump
but
when was the last time you change the air filter?

 

My power steering pump moans with a slight turn of the wheel at first startup. I equate it with her just being a little old and she just takes a little longer to wake up and prepare for the day.

 

air filter changed about 1500 miles ago..

 

I suspect it's coming from the Idle Air Controller (IAC). it sounds like your noise is happening during the elevated idle speed period that follows a cold start. The IAC probably has some carbon/dirt build-up that is causing an acoustic anomaly when its opened in just the right position.

 

Yea the IAC silencer has most likley been deleted at some point. It's a total 4.6L thing. Some call it the black box. Anyway, once deleted the IAC can sound off. This can occure right away or at some point in the future.

So someone hacked the black box off your IAC tube is my guess.

 

Ok I will check it out--but I don't think the IAC has been messed with... I will clean it and see what happens. Thanks Mud