This article shows you how to replace an alternator on the 7.3L Powerstroke Engine. This "how to" article was performed on a 2000 Ford Excursion with the 7.3L Powerstroke Diesel. The concept outlined in this article may also be applied to alternator replacements on other vehicles, too.
At the time of this installation, my battery light had turned on while driving -- indicating a problem with the charging system on my Excursion. Upon further investigation with my voltmeter, I determined that the batteries were outputting an acceptable voltage (11.85 volts) with the vehicle not running. With the vehicle running, the output of the alternator was only 11.8. Since this should be in the 14.0 volt-range (with accessories turned off), I determined that the alternator had finally failed after 155,686 miles. Not a bad lifespan.
The goal of this install is to show how to remove an existing alternator and replace it with a new or refurbished alternator. In my case, I went with a refurbished Napa alternator with a 3-year warranty. Napa also offers a more expensive lifetime warranty refurbished alternator, and a new OEM alternator, neither of which they had in stock, so I opted for what was available to me as I needed my Excursion back on the road.
I purchased my refurbished alternator at my local Napa store. Any local parts store should be able to provide a replacement alternator. There will most likely be a core charge, so save the box for when you return your used alternator for the core refund.
Step 1: Remove belt from alternator pulley
1.) Locate the alternator pulley (top-right most pulley on the front of the 7.3L Powerstroke).
2.) Locate the 1/2-inch tensioner hole (for 1/2-inch ratchet (no socket is required)
3.) Insert 1/2-inch ratchet, use extension bar, and loosen the tensioner (pull up). This will require some leverage, so be positioned correctly to move the belt if you don't have a second set of hands.
4.) Lift the belt off of the alternator pulley and slide it towards the front of the vehicle.
5.) Gently let the tensioner go back into place -- be careful not to lose your grip on the ratchet as it can snap back.
6.) Leave the 1/2-inch ratchet in place with the extension bar positioned on top of the upper radiator hose -- this will also help keep tension on the belt and prevent it from falling off the other pulleys.
7.) Secure the belt to prevent it from falling off of the other pulleys. I used a long screw driver to hold the belt in place while I worked on the alternator to prevent the belt from moving.
Step 2: Remove old alternator
1.) Peel back the rubber grommet around the positive cable terminal on the back side of the alternator to gain access to the 10mm nut.
2.) Using your 1/4-inch ratchet and 10mm socket, remove the 10mm nut from the positive terminal. Be careful not to touch the wire to any metal in the engine compartment (to avoid sparks).
3.) Pull the positive cable off the post towards the cab of the vehicle.
4.) Wrap the positive cable end in electrical tape for safety (to prevent it from making contact with other metal).
5.) Use a thin, flat-edge screwdriver and pry up on the 2-wire plug to loosen the plug. Pull plug off of alternator and set the wiring harness aside.
6.) Use a 1/2-inch socket and a 1/2-inch breaker bar to loosen & remove the 3 bolts on the alternator.
Step 3: Install new alternator
1.) Before installing, remove the positive post nut (to avoid dropping it down the engine compartment and losing it!).
2.) Position new alternator onto bolt holes.
3.) Hand-tighten all 3 bolts.
4.) Tighten all 3 bolts.
5.) Reconnect 2-wire plug.
6.) Reconnect positive wire using new nut provided on alternator -- avoid pinching the rubber grommet under the nut to ensure the best seal (keeps the terminal from corroding).
Step 4: Reinstall belt & test
1.) Loosen the tensioner again (by pulling up), remove the screwdriver you're using for leverage to keep the belt tight, and reposition the blet onto the alternator pulley.
2.) Double-check that the belt is still in all of the proper grooves on the grooved pulleys.
Note: Depending on how long your alternator had been bad for, your batteries may need to be charged like mine did. I simply jump-started the Excursion from another vehicle.
3.) Turn all accessories off and start your vehicle.
4.) Test your new alternator by using your voltmeter and touching the positive voltmeter wire to the positive terminal on the back of the alternator; touch the negative voltmeter wire to the negative battery terminal in the engine compartment. Mine read 14.2 volts at the alternator. Yours should be in the 14-volt range with the vehicle running. Each battery will read about 0.3-0.5 volts less than the alternator; this is normal.
This is one of the easier replacements you can do with basic tools in your garage. The alternator is also one of those things that will completely disable your vehicle if it goes bad. If/when your battery light goes solid, test your batteries and alternator right away, or you may find yourself stranded with a vehicle that cannot start.
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