FallGuy44

2001 F150, 5.4 195,000 miles. Second alternator. (I want to say it's about 4 years old)

I am driving home last night, dash lights were at a steady dim, A/C wasn't blowing as hard, battery gauge had dropped etc. I get it home thankfully, and put it on a multimeter while running with the lights on. I get 11.6 volts. So I am thinking bad alternator for sure. Battery is a year old.

So today, before I start buying parts I wanted to double check. So I take it to Advance for their free testing and it passes with flying colors.

I am thinking I should just replace it as it seemed to go bad last night so it doesn't strand me somewhere. Thoughts?

*Also, I can't remember what Amp Alternator is in there now. If I go with a 130 Amp replacement, do I need to upgrade battery cables? Thanks!

03f15012

The battery might be only a year old, but it never hurts to get it checked. The alternator in my truck went out for the first time about a month ago.

FallGuy44

I had the battery checked with the alternator. Both tested good.

Someone mentioned to me a bad AC compressor could maybe cause this symptom. I had a 1:15 drive home. I shut the AC off about 45 mins into the trip and nothing changed, still dimmed dash lights and low battery gauge etc. So I am thinking this may not be the case but was wondering if this is possible.

mkraffert

Did you try testing the alternator and battery with everything running you had running when you had the problem? Maybe you have a short or overload in one of the circuits that was drawing power, and once the circuit was off, the overload went away?

ibd2328

iTrader: (2)

Might wanna check that your tensioner and tensioner pully are good. Could be cause the belt to slip thus not making your ac compressor to not work as desired and loss of amperage.

On the other hand, voltage regulators and the alt field can go in and out when they are failing. I would check my tensioner, then recheck voltage. Check the voltage on the battery before testing then compare.

Jay87LX

All of these are good ideas pointing in the right direction. The only thing I would add is I have seen in the past that an alt may test good when cold but as it heats up its voltage output diminishes some

I am under the assumption though that all Ford V-8 trucks use the 130A alt- I believe the upgrade is to a 200A from Ebay

FallGuy44

Ok, so I put the battery tender on yesterday until it showed fully charged. I did not start it till today. I went out just now and did some tests with a mutimeter.

Before staring and right when I opened the hood the battery was showing 12.6-12.7. Not long after it dropped down to 12.3 and stayed there. I got another multimeter to double check and it was steady at 12.3. The hood light was on but nothing else.

I then started the vehicle with no accessories on. It was showing 14.6 or so. I turned on the AC and head lights just like the other night. Slowly it started to discharge. It got down to 12.17. I turned the accessories off and it went back up to 12.30 but again started to discharge slowly.

Shouldn't the battery be at 12.6 or 12.7 with the vehicle off? Is it possible the battery isn't holding a charge making look like a bad alternator? I think the battery is under warranty. Should I start with a new battery and see if the symptoms continue or do you think it's definitely the alternator?

03f15012

I'm curious about if you are getting a battery light. My alternator went out (or at least was starting to) and I was getting it. Truck always started fine for the next day or two, and I did see fluctuation in the gauge. My battery is at least 3 years old, and I'm betting it was the original alternator too. So, if your battery light isn't on, I'd be unsure if it was the alternator or not.

FallGuy44

No, battery did not come on at any point. At what voltage does the battery light come on? Is it possible that it just didn't reach that point yet?

Also how can I tell if the tensioner is bad? The belt feels tight and the tensioner does not move by hand.

FordmanUGA

This may be a dumb question but have you checked all of you cables and connections for any corrosion, rust, or possible broken strands inside the cable? Sounds like you're getting a random disconnect from time to time.

Regardless if the battery were going bad or not, your alternator should run the truck fine unless your battery is totally shot. But I've had batteries totally crap out on me and never know it until I shut the truck off and tried to start it again.