Hi im new to the site. I have a 2006 F-150 5.4 FX4. The problem im having is the battery gauge shows a spike( normal reading shows guage at half way... And the spike goes almost 3/4 of the way for a few secs and goes back to normal). The alternator was replaced earlier last year with a factory one. Past few weeks ive been noticing the spikes and ford replaced it once again. No change in this. Replaced the battery to be on the safe side and no difference. Whats the next step i should do? Thinking about getting it scanned to see if anything is showing up. In that charging process i guess the pcm tells the alternator how much to put out. Could the pcm be bad? Or the alternator be bad ( the internal voltage regulator ) ? Or a wiring issue with one the fuseable links? Thanks for any info and steps to keep going.

 

i have the same problem, haven't found a solution or changed anything just yet. the battery light comes on, sometimes stays on, sometimes goes out. if i found a solution i will post in hopes to help the next victim. good luck.

 

Don't judge the charge by the gauge because they are almost useless. Have you checked with a voltmeter at the battery terminals when running and when off? Let us know what you are at.

 

bad alt, a winding in armature is grounding out and going full charge, seen it many times with rebuilt alts. You could use an actual volt meter hooked up to a power point or cigar lighter to verify spike, but if battery light has ever flickered than its definately alternator

 

i had the same issue about a month ago, light would come on for a while then go out and then gauge started going 3\4. just decided to replace alt. and everything has been good since.

 

seems like a common problem with alternators crapping out, i tested mine and it was providing proper voltage. I guess I will soon be changing out my alternator.

 

Yeah. With one of the spikes it went to 15.3-15.4volts. This the second alternator... Not a rebuilt one but a factory one. It happened again today and this time i noticed a pulley/bearing noise when the voltage spiked. As soon as i stopped it went back to normal. I checked the pulleys and noticed that one of the idle pulleys i could move easily with my hand and i noticed the belt tensioner had more play( wasnt tight) replaced both of those this evening and hopefully this will change the voltage spikes. Its odd that noise came with the sudden spike in voltage. Do i need to look any where else or that noise i heard the alternator going bad( less than a month old)?

 

Also it went so high today that the battery light came on with the noise.

 

if those changes work, please report back either way i guess. i noticed my tensioner was a little jumpy while i was looking over the bay and testing the battery/alternator voltages.

 

where did you find a "factory" alternator?? Also a loose pulley or tensioner would would undercharge, NOT overcharge!