Hey guys,

So today my battery light popped on a couple times. took it to Oreillys auto and both battery and alternator checked out good. I am thinking this could be a Belt tensioner going out causing the belt to slip and alternator not charging properly.... The red battery light only pops on after I "get on the gas" and only stays on for about 45 seconds.... I am sitting on 120k on the original belt and tensioner, is anyone in agreement with my diagnosis or have any other ideas?

 

Thats a good starting point, especially at 120K.

 

i also hear a slight when when on wide open throttle... I am assuming thats the tensioner puller and\or the idler pulley

 

Could be, take off the belt and see if the tensioner is loose, or easily moved by your hands.

 

I’m thinking alt...

 

I'm with techrep, alt or battery, but would start with replacing the belt and checking all pulleys. They do have 120k miles on them, so it's probably time for something to go. Keep in mind the tests O'Reilly's can do are not always definitive.

 

There's a bridge diode assembly in the alternator that may be failing intermittently. This diode assembly converts AC to DC.
At 120K, your belt and tensioner are very overdue for replacement, so tossing that in as fix would not hurt your wallet if it does not cure your current charging issue.

 

and when replacing the Alt... use Motorcraft only

 

so I changed both idler pulleys, belt tensioner and serpentine belt..... I drove it about 10 miles from home and BOOM!!!! the dang battery light popped back on... ****!!!!

 

Well then like the others said, alternator. Just know that you should be good for the life of the truck where the charging system is concerned after the alternator replacement!!