We have an 04 FX4 nearing 100,000 miles. It's stock other than a K&N air filter and we put in an alpine deck.

This has only happened twice... When braking the headlights dimmed and the flow from the heater slowed. Then we heard this high pitched squealing/squeaking sound. As soon as he stepped on the gas the noise stopped and everything went back to normal.

The truck was going to the dealership to replace the IWE and a clutch plate. So we had them check it. They said they couldn't figure it out... Apparently the alternator is testing fine, no mention of belts or pulleys.

So here I am hoping you guys can give me an idea? It's only happened twice but it's bugging me, lol.

 

Alternator pulley? Didn't by chance get a look at the dash did you to see for a drop in voltage, did you?

Could be the battery, how many times have you changed it? Maybe its losing its ability to take a charge. Ever have a problem with stalls or slow turnover at start?

 

The engine is decelerating fast and dipping in idle causing the voltage drop, Ford ALts are notorious for this issue. Replace the serpentine belt and check the alt pulley real well for glazing, replace if necessary and your problem should go away. If it doesn't then its time for an alternator. Their bench top testers only test at highway speeds which is why your alt is testing fine. Get it down to around 300-500rpm and it will show its head, the regulator begins switching on-off-on causing the dimming.

 

Thanks... Sorry I forgot all about posting this.

We didn't notice any voltage drop but we have never changed the battery. We just bought the truck Nov/07. No problems with slow turnover or stalling.

I called the dealership and talked to the guy that worked on the truck. He said the belt, pulley and alternator are fine. Yeah ok... so we imagined the entire thing. LOL

I guess we will start with the serpentine belt and check the pulley. Thanks again.