Hi guys,

2003 F150 4x4 scab 5.4 104,000 mi. I just got stuck in the desert with a low battery but am unsure if it's the battery, alternator or something else. The battery I took out was only 1.5 years old or less but I replaced the battery and it started fine and has been running fine. However my scan guage II said it was charging 13.4-13.6 yesterday in the heat right after I installed the new batt (102* outside heat) but this morning it was charging 13.5-13.9. I'm from the old school and thought it should be charging 14.6-14.8. With a good new battery what should the charging volts be? I would just take in the alternator and get it checked but I only have one car and it's a hell-of-a bike ride to the nearest auto parts house.

If the "old" battery checks out good under a load test is there anything else it could be besides the alternator? I slow charged the old batt last night.

Thanks again for you help!

 

The internal regulator will drop the charge voltage/current as the batt charges up.The voltages you mention seem to be good..usually any charging voltage between 13.0,and 14.0 is normal.It will depend on the "recent" load applied to the Battery. If it just finished cranking the truck,the voltage should be somewhat higher than it will after it has run awhile.
The next question is.....is this voltage pure DC,or is there some AC being fed into the system.
The Alternator initially creates AC voltage,this voltage is converted by a rectifier bridge consisting of 6 diodes. These diodes serve two functions...first they convert the AC voltage to DC voltage,and secondly they create an electronic"Dam" to keep the battery voltage from backing up through the alternator when the engine isnt running.If one or more of these diodes become defective(short,or open) it will allow a proportional amount of AC voltage to enter the charging system,and can cause a battery failure.It can also cause the battery to drain when the truck is not running.
I figure a battery thats 1.5 years old shouldnt be bad.I guess it happens,but you may be wise in having the alternator checked.....

 

Thanks N59 I think I'm going to replace the alternator as well just to be sure. It has over 100K on it so havng a now one wouldn't hurt and may help keep me from getting stranded again.

Thanks again for your help!

 

My alternator died recently too. I was driving out in the middle of nowhere, at night, in the North Carolina mountains, and suddenly all the lights started getting dim. It stayed that way for a few minutes and had me rather worried. Finally, like a light switch flicked on, everything came back to normal.

I made it to my hotel, and had it checked the next time and everything came back normal. Weeks went by, and it did it again, close to where I live. I had it checked again, and it seems that something was sticking open in the alternator. I believe it was a diode. So, I replaced it and have never had another problem. It's a relatively cheap and easy fix, and I went ahead and changed the belt while I was at it.


Good luck...

 

Thanks, I'm going to do the same.

 

You might want to check into alternator rebuilding shops. I have had many rebuilt on my farm tractors, pickups and cars. I have not had to have a return visit to date. I just had a total rebuild on my '99 f350 and it was $46.00 vs $200.00+ elsewhere. It was the diodes spoken of in the previous post. While the case was opened, they replaced bushings, bearings etc.

 

I looked into that and here it's $100 vs $140. 90 day warranty vs lifetime warranty so for $40 I took the lifetime warranty and bought a Reman from Vatozone.

Thanks for the info though.

 

If the alternator was putting out 13 volts, Id say the problem wasnt the alternator. It could just be that the heat got to the battery. Granted, the battery was only 1 1/2 years old, but it could have just been a freak failure.
If you keep having problems, you may want to look into it being a bad voltage regulator or a bad ground. Either of those things can cause problems.
A couple years back my brother had similar problems with his '99 F-250 and the problems persisted even after trying changing the alternator and battery. It ended up being a bad ground.

 

With the engine running, voltage at the battery should be 13.5 - 15.0 volts. Good luck!

 

With the engine running it hits 14.0 after cranking up in the morning and then goes between 13.4 and 13.8 during the day, never over 14. The volt meter at Azone said it was fluctuating between 13.7 and 13.89 at idle and a warm engine. Just too iffy not to spend the $150 and be done with it hopefully.

The old battery tested "bad" according to Azone guy but I think that's what he's supposed to do. Test it under load until it comes back bad. The first test said to charge and retest but I had just charged it so they tested it again and it failed. I think it's a bunch of BS and no matter what the battery and alternator would fail according to Azone.

Aren't regulators built into the alternators these days?

Can anyone recommend a good battery load tester that I can buy?

Thanks again for your help!

 

Go ahead and put the tools you used to change that alternator in the truck and leave them there. You'll spend the rest of your lifetime removing and replacing that Autozone Reman.
JL

 

Where do you suggest getting one?

 

With the voltages while running being mostly in the range of 13.5 - 15.0, then I would say that the alternator is good and would agree that the battery is the problem.
What does the battery measure when the engine is not running?

 

For a reliable unit-you have a few choices. A new OEM alternator from a dealer or Motorcraft distributor, a pull from an RV/truck conversion company,or a trip to the local starter/alternator rebuilt specialist. There's a seller on ebay that sells new take-offs from truck/RV conversions. I've bought 2 from them over the years to replace failing OEM alternators,and have had good service from them and the alternators that I've received.
JL

 

Hello, I need an answer to the 4.6 alternator wiring. What does the middle wire on the alternator do and where does it connect to in the plug harness by color? I got a new harness but it was cut on the plugs so I have to rewire it with different plugs. I could use a wiring diagram for the alternator circuit on my 97 f150 if anyone could help me out.