Hi, I have a Ford F-150 4.2L v6 1999 Truck and I'm having problems.
I hear a whining noise when I press on the accelerator. It goes away if I let up on the accelerator. Need some advice please.

 

Welcome to the site..

Noises are always a challenge at the forum level..

Does the noise occur when stationary raising/lowering the RPM?

If no driveabilty/idle issues, or check engine light, most times a 'whine' will be either an alternator or possibly the belt tensioner pulley or the belt idler pulley that may/may not be intermittent.. Anything that runs on the accessory drive belt could be suspect, but 'generally' the power steering will groan when the steering is turned side to side but can give a whine, but tends to be more noticable through all the engine speed changes.. Drive belt itself can chirp or squeal.. Another possibilty is the 4.2 is equipped with a 'cam synchronize' and sensor that looks like a short distributor mounted in the front of the engine block.. They can run dry internally and will usually squeal/chirp but can give off a high pitch note..

A good way to diagnose base engine noises over belt driven component noise would be to remove the accessory drive belt and see if the noise stops.. If so,, it pins the cause to the belt driven components, and, it takes the cam synchronizer out of the diagnostic loop as well as any base engine noise.. With the belt removed, sometimes you can spin the alternator as well as the belt pulleys and at times the source can be isolated.. At a guess,, I'd say the alternator as the #1 cause for a whine if the noise is high pitch, steady, and ranges with engine speed.. If you can duplicate the noise stationary,, you might try and listen at the alternator, or 'carefully' place a long screw driver or long socket extension against the alternator case to pipoint the noise.. Same with the P/S pump, tensioner/idler, and the cam synchronizer if the belt is removed (but can be checked with it installed)..

Not a buzz or rattle though?