1994 F250 alternator

[Alan L.]

My truck battery keeps running down. According to what I read, it could be the voltage regulator in the alternator drawing the batteries down when the engine is not running. I am considering switching out the alternator, but need to see how to loosen the belt to get it off/on. The alternators I have replaced you loosened a bolt and moved the alternator itself to reduce tension on the belt. This alternator appears to bolt into place permanently, so have to loosen the belt somewhere else. I would figure that would be done by putting a wrench on an idler pulley and pulling it to loosen the belt.

In these pics, there are two idlers, I wonder which one I would loosen, there is one directly below, and another to the right (looking at the front of the engine). Don't know if the pics are detailed enough to be able to tell.....

 

[anojones]

I'm not sure the specifics of which engine you have, but your picture shows a serpentine belt. The belt should wind around a pulley that's acutally a tensioner. Put a socket on that pulley/tensioner and move it away from the belt (it's spring loaded) and then you can slip the belt off. Sometimes on those Fords the tensioner has a square hole that will fit a 3/8th ratchet without a socket- you may need a breaker bar to get it to move easily. Be careful as the tensioner is spring loaded and if it snaps back you can get your hand between the tensioner and the wrench. Usually there is a sticker in the engine compartment that shows how the belt goes on, if not make sure you draw a diagram before you pull it off.

Also- if it is happening overnight, it could be a drain from somewhere besides the alternator, some of the plugs that go into the alternator will short and cause a draw and you can just replace the plug. Before you replace the alternator you might try unplugging the alternator and seeing if the battery still runs down, the draw down might be from somewhere else. If you have a meter you can use it, if the voltage is low- pull fuses until the voltage goes back up may help isolate it. Try http://www.ford-trucks.com/forums/forum28/

 

[Ductape]

The small pulley directly below the alternator is your spring loaded tensioner.

 

[Dmace]

The small pulley directly below the alternator is your spring loaded tensioner.

Yup, put a large ratchet or breaker bar on the bolt in the center of the arm and turn left. You will have to hold it while removing the belt, a second hand helps here.

Also, if you want to test the alternator before removing it just put a voltmeter across the battery terminals while the engine is running and see what the voltage is going to the batteries. It should be between 12-13 volts while idling and between 14-15 volts while the engine is at about 3,000 rpms and up. I see you have the first year Powerstroke 7.3l, I had a 94 also but it was the non-turbo IDI 7.3l diesel and the alternator was a 130 amp unit and almost $200 so if you remove it get it tested before replacing so you are not wasting money.

 

[Shimon]

If you suspect the voltage regulator is keeping the alternator alive while the engine is off then there is a quick test to see if it's true. The rotor will be energized which makes it a big electro-magnet. Put a screwdriver or something metal near the bolt on the pulley or at the very center of the rear of the alternator (near the bearing) and it should be magnetized. If it is (when the engine is off) then the alternator will drain the batteries. If it's not magnetized then it's probably fine. Also the alternator will be warm to the touch (assuming the engine is cold).