I own a 1996 F-150 v8 302 and about a week ago the battery died on me on the highway. My first thoughts were bad terminals, or alternator. So I replaced the alternator yesterday and the serpintine belt seemed tight. But when I put the new alternator on and started the truck up the belt wasnt tight enough to spin the alternator. So I looked at the tensioner pulley and it was raised to the top in the farthest position to tighten the belt, yet the belt was still loose. I can't figure it out, I even replaced the old belt with a new one and it's still loose. Any help or suggestions would be appreciated.

 

Maybe you have the belt incorrect or maybe the tensioner went south. If you have pressure when moving the tensioner to install belt the tensioner is fine. If there is noresistance then the tensioner has failed.

 

Alright well the belt is definetly loose, so I will go get a new tensioner pulley any recomendations on brand?

 

Yes, double-check that you have the proper length of belt. You can always get the number off of your existing belt, and go into the parts store and get a slightly shorter one.

 

It was said before, but make double sure of the routing around all the pulleys and idlers.

 

I don't know about a '96 302, but on my '93 460, there are two belts: one serpentine with a tensioner for everything except the alternator, and another micor-groove, serpentine-style belt just for the alternator. That one doesn't have a tensioner; the tension is set v-belt style, by adjusting the alternator position...
Assuming yours is a single serpentine belt, and the tensioner is at the end of it's travel, you need a shorter belt...

 

Like white 97 said , check the belt routing , theres a few ways it can go on , sounds like your going on the wrong side of a pulley.....

 

Yeah, what lew & white97 said. I was assuming that the belt is routed correctly.
(I know, when you assume...)