on my 05 5.4
headlights and dash light dim when passing or getting on it pretty hard the air coming outta the blower vents decrease as well
i thought it was the belt slipping so i got a new belt.....nothing
so i got a new tensioner.....nothing
let me know please
thanks

 

Alternator and/or battery. Mine did similar when the alternator quit, or when the battery is almost kaput. Worth checking into. Curiosity, what's a tensioner go for $$$?

 

the battery is new but i guess possible ill have to do an alternator test i guess

they are $100 ill sell you my brand new one that didnt fix my problem lolol

 

my first guess would have been an alt..

 

could it still be the alt. even if its keeping the battery charged?

 

If your battery light comes on/ flickers on hard acceleration it is the alternator. If the light does not flicker it most likely the battery. If the light doesn't come on have your battery load tested.

 

Sounds like the alternator is not keeping up under a load.

 

ya i was thinking that too but i was able to pull the belt off the ideler pully if i wanted too and so i thought the belt was just loose
and also on hard acceration when it shifts, sometimes the belt squeks so thats another reason i thought it was loose

 

Mine started Sunday night on the way home, alternator light flickering on when rpms went over 2000: Drove it about another 100 miles , light stayd on more and more till it died on way to Pep Boys (I was 1 mile away)

Dropped dead at a red light, couldn't even use flashers to divert traffic Got towed (at least It waited till Monday and not Saturday night when I drove home 60 miles in a blizzard)

Rebuilt lifetime alternator at pep boys $159 installed another $95 plus tax

(and guys dont laugh, I would have installed it myself if I had tools and wasn't on the way to a biz meeting)

 

well my lights not on or flickering at all
ill just have to do a few test

 

its your battery.

 

Did you find out anything Whitelifted 5.4. I have the same issue and have replaced the Battery , Belt and Alternator but the lights still dim on hard acceleration or just reving it to 4500-5000 rpms I did notice that if you slowly creep up to to 4500+ rpm it does not dim you might have to hit 4750 to 5000 if you hit the accelerator harder it dims at 4500

So I'm thinking it's a tensioner or something dragging connected to the belt.