Hi guys this morning my battery light came on and off a few times. When I got to work it was off so I borrowed a scan tool from a buddy there that has live data. While running it had just over 14 volts. He let me use it for my ride home. I let the truck warm up for 15 minutes never dropped below 14 volts, as soon as I got a 1/2 mile up the road it dropped to just over 12 volts. The whole way home about 19 miles it would stay about 12.4 then jump to 14 for just a short time. By the way it's a 08 F150 5.4 with 75000 miles. Thanks for any help.

 

Time for a new alternator, that one is about to die completely.

 

Or you could try a rebuild kit.

 

Hey guys thanks for the replies. So I got a new alternator today did the belt while I was at it. Just wondering what the normal volts should be? While driving tonight they would be at 14.2 then drop to 13.3 for a mile or so then jump back to 14.2 back and forth about every mile. It seemed like the dash cluster would also dim slightly when the volts dropped. The battery is only a few weeks old also. Am I worrying for nothing or could I have more problems?

 

It's still not fully fixed if it's doing that. Should be constant 14 or so.

 

Keep in mind that by 08, Ford had gone to the PCM-controlled charging system. The PCM not only monitors the output of the alternator, it also controls its output, keeping it between 13 and 16 (absolute maximum)volts, and can alter the output voltage based upon engine load and battery temperature (inferred from the IAT sensor).

I'd keep an eye on it for the moment. I'd also check with the scan tool to see if any charging system DTCs are set, generally a P06xx. If the voltage stays above 13, it's probably okay, it may just be recovering from the lack of proper charging. If you have an automatic charger, I'd hook that up for an overnight charge.

 

This is dead on.

https://www.f150online.com/forums/el...ml#post4969019

https://www.f150online.com/forums/el...ml#post4974725

Mine does the same thing - ever'thang is healthy.

 

I was also going to ask about temperature when you are driving.
IAT & ECT are used when calculating the battery temperature which sets the charge voltage on the 04+ MY trucks.

Have you charged the battery on a trickle charger since you had the issue, or are you trying to use the truck's alternator to charge it ?

Did you ever check the battery voltage after sitting overnight, with a meter ?
- Curious how many times the battery was at 12.3 VDC at rest or lower, you might have shot the battery in the head with the alternator issue.

15.5 VDC is the end of the normal range for charge voltage, you are still in the normal range with the values you posted.

The other question that has not been asked, what modification have you done to the truck ?

 

Hey guys thanks for the replies. Been busy with work and haven't been on in a while. I charged the battery the other day as I was seeing drops to 12.3 volts a couple of nights so far seems good 12.5 last couple of mornings. I have also noticed the volts spike to 15.1 a hand full of times over the last week or so including today not sure if this is also normal. As far as temperature while driving I live in MA and it has been in the teens pretty much for a few weeks now getting down to around 0 in the mornings. I don't know the IAT or ECT temp. As for mods I have the gotts intake mod, exhaust, and a remote start. Not sure if I'm just driving myself crazy thinking something is wrong or if their is other things I should be checking. Thanks again for the help.

 

Have you checked the battery connections? Not only the ones at the battery posts, but also the one at the end of the Gnd cable especially. It is exposed to all sorts of environmental damage and can become faulty.

Also, how about the cabling from the alternator to the other ends?

Your description of your problem sounds to me like an intermittent poor connection.

- Jack

 

Have you replaced the battery since changing the alternator ?

the overnight drop to 12.3 seems a bit excessive and with the issues with the alternator before you might have shot the battery in the head.

15.1 volts, while not the norm, is not outside the normal range depending on the charge state of the battery and the temperature.

Either a proper load test or I would just go in on a new brand name battery, before you trash the alternator that you just installed.

It could be something causing a discharge overnight, but with the issues you have had I would take a SWAG that the battery has been abused too much to expect it to act correctly.

Of course battery cables always could be an issue on a 10 year old truck, but I am going with the horses not zebras route here ( eg: what do you think of when you hear hooves )

 

It was the intermittent nature of the problem that made me think of zebras, SSCULLY. But, I did give the battery itself passing consideration.

- Jack

 

Thanks guys the battery was new the beginning of January got a die hard platinum. The negative terminal was corroded when I changed the battery. The other day when I charged the battery I noticed corrosion slightly starting again. I had cleaned it pretty well when I changed the battery.,and cleaned it again when I charged it.

 

Corrosion around battery terminals is normally caused by gassing, which indicates a charging problem. This problem is usually a result of a battery that is being "boiled", for lack of a better term.

You may want to check your electrolyte level. If low, in any cell, add distilled water to bring it up to spec.

But, I'm back to the connections at the other ends of the battery cable and the alternator cables. Are they sound?

Note: I'm still hearing the sounds of zebra hooves, or maybe it's gnus?

- Jack

 

You now have an AGM battery and you charged it out of the truck ( or at least disconnected ) with an external charger.

One big question here, do you have an AGM charger and set it to AGM when charging the battery ?
- A standard trickle charger for non AGM batteries will trash an AGM battery and void the warranty on the battery ( at least Odyssey calls this out, Sears I do not know ).

The other thing, 15.1 is in the normal charge range for a battery, depending on the conditions, so 15.1 can be normal.
- It would point to another issue if it was all the time.

Is the charge / battery light illuminating anymore ?