'91 alternator?

[sunwoman154]

My son has a '91 Explorer that has 176K miles on it. He noticed it was getting harder to start. We checked the water level in the battery. (we live in AZ and it will be 111 today) Next day he lost power on the way to work. Got him jump started and got home. Our guess is the alternator. How difficult is it to replace? Does anyone have access to online diagrams for location and how to replace? Thanks!!

 

[Jason94sport]

Not hard to replace.
Take intake tube off.
Loosen the belt by rotation the tensioner
Remove belt off pully
Remove 3 bolts holding it on
Take out & replace in reverse order
Depending on the alt you may have to swap the alt pully

 

[alexefron]

you can check to see if its working before you go at replacing it. To check it get a volt meter, hook it up to the battery, start the engine, and make sure the voltage goes up. If it does your altranator is ok, otherwise its not working right.

 

[410Fortune]

The 91 4.0L has a weak alternator, if yours is still stock I believe it is only 65 amps or possibly 80..
these units have a built in voltage regualtor.
With the truck running at idle you should have 14.4v at the alternator.

If you take the alternator to a car parts place they can bench test it.
There is an upgraded unit, 110 amp I believe you can get.
I used this unit on my 4.0L engine, after going through about 4 Autozone lifetime warranty rebuilt specials...

I can get the truck model year and Bosch part number if you want to upgrade to the higher amp, much better unit for your 91. I think it was $135 new, some small wiring changes were required (very small)

any local starter/alternator guy can sell you a new 90 amp unit, or rebuild yours for about $100. It is recommended to also replace the pig tail wiring that leads into the alternator.

Check your battery cables, early explorers are known for having weak connections/corroded cables.