Team,

Original equipment alternator lasted me 11 years and replaced with a lifetime warranty Duralast. 3 years and 2 days later, alternator shot, but free replacement. This was 2 months ago. Today, my battery light came on and alt gauge started to head towards "L". 5 minutes later, all gauges shut down and the truck stalls. Could this possibly be the 2 month old alternator failed again?? The first two times they failed I did not get the battery light coming on. I have it on the charger overnight and I will start it tomorrow morning and check the battery voltage while it is running. If it is not above 12, and falling I think it must be the alternator. Thoughts are appreciated.

-John

 

Forgot to mention 2001 F150 4X4 SuperCrew, 5.4L

 

Make sure to take a voltage reading at the large lug on the alternator with the engine off. If you get nothing, there may be a fuse or fusible link blown in this line. Also, I believe the later trucks like yours also had a smaller fuse in the underhood fuse box for the regulator portion of the charging circuit. If everything checks out, must be another faulty one. That's the bad thing about some of this stuff. Yes they give you another one for free, but your time taking it off and putting another one on starts being worth more than getting free alternators.

 

Dave,

This "large" lug, is this the one with the nut? Do I check voltage between the cable and lug?

 

Yes, that's the one with the nut. That's your output wire. The older trucks had a fusible link in the wire, and I am thinking some of the later ones had a large fuse in this wire, not sure on that though. But after it goes through the fuse it goes directly to the battery +. So you can put your meter lead on this nut, and put your other meter lead to a good ground. You should get battery voltage if this wire is still good to the battery and the fusible links/fuse is good.

 

ok, I checked it and got 12.5, same as battery. Probably alternator then??

 

Back on the road. Ended up being alternator. Actually originally bought lifetime warranly, remanufactured. I upgraded to lifetime new. For all my inconvenience, AutoZone upgraded me for no charge. I guess mentioning my $175 towing bill several times paid off!!

Thank you for all your help,

-John

 

Ok, update;

Two weeks to the day, I did something kind of stupid. While helping someone load firewood in the dark, I used my truck to "light up" the work area. 20 minutes max and battery dead. Jumped it and let it run about 30 minutes. This morning I checked it and had 12.5 volts. I noticed a little "drag" when I started it. Shut it off and tried again. Drug, but never started. Bad battery? What is acceptable for volt drop while cranking? Somebody mentioned a bad battery could have caused my alternator to go bad.

Thoughts on voltage drop??

-John

 

Voltage can drop to around 10v, all depends on how cold it is and how hard the engine is to turn over.

Just take it to the store and let them put their tester on it.

 

Depends on the reserve capacity of the battery, but a charged healthy battery should handle 20 minutes headlight use. Since it did not, it may be sulfated.

Measurement of the open circuit voltage is a very accurate way to determine the health of a battery, but it has to first be fully charged (takes several hours with a retail charger) and have the "surface charge" removed. This is why conductance testers are so popular for warranty use, they do not require a battery to be charged completely for testing. Personally, I would avoid pairing a new alternator with an old, sulfated battery. Or a dead one, on any alternator. Believe it or not, they aren't really designed for it. It doesn't do 'em any favors, put it like that.

Typically a fully charged serviceable battery will not drop below 9.6 volts at the terminals while cranking for ten seconds. That's minimum, a healthy battery will be more like 10.5 ; it's important to use an outboard charger on the battery anytime a jump is required.

Don't use the engine alternator for this purpose unless you plan on driving for twelve or fifteen hours, still it's hard on the charging system. It's possible to overcharge a battery with a retail outboard charger but it takes dedication. Winter is coming on, now is a better time to make sure things are good to go than when snow and ice is on the ground.

 

I put it on a charger yesterday to get it to start and drove it awhile. Battery tested 12.8 volts. I let the truck sit outside overnight, temp dropped to about 32. This morning battery was 10.43 and dropped to about 7.8-8.1 while cranking. Think I might pull it out and test/replace.

additional thought??

 

Replace the worn out battery.

 

Sounds exactly like a shorted cell with voltage at ~ 10.5 and why it crapped out after 20 minutes of headlight use. Try to get a fresh battery and not one that's been sitting on the rack for nine months. Check the date code before purchase.

It pays to take the time to charge up your new battery thoroughly before installation. This usually takes several hours at a low rate.

New batteries are "hard" and take a dozen or so starts before they will reach full capacity as well.

 

Thanks for your help. Fresh battery installed @12.5 volts and seems good. Old battery failed the load test. Was 5 years old and fell into their "64 month prorated" warranty. Return for my $10, right?? Wrong! $67 toward new battery, almost 1/2 the cost. Felt like I finally won one!

 

Happy for you! Nice!~