Truck... ALT or Batteries?

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brendonv

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I'm not good with electrical, the battery light on my Ford chip truck is flickering. Batteries are crappy Napa's from Feb 2008. I've noticed the last few mornings the truck isn't starting good, like the glow plugs are shot. Battery light flickering today is making me think the GP's aren't getting enough juice to warm the ol' girl.

So how do you know when it's the batteries and when it's the alternator, without taking them out of the truck to get tested?. My auxiliary idle control unit was showing 11-13 volts when I was driving.

I'm thinking it the batteries, but I really don't know.
 
I think if you disconnect the battery with the truck running, if it keeps running, the alt is good
Or...
Pull battery in front of like NAPA and have them test that for free.
 
If you have access to a multi meter, test the alternator at the big wire coming out the back of it. Should read 13 something. Don't expect to see 14. Your auto parts store, as mentioned, should be able to test everything right there in the parking lot. Also, make sure your battery cables and clean and tight, and, like I found out recently, check your engine ground.
 
Yup.

2008 is getting a little long in the tooth, especially for a battery starting a deisel. But testing is a better plan that just replacing on a guess.
 
If you do have to replace the batteries, and are looking for some vicious batteries, I recommend the optima yellow tops on a diesel. My wife nearly flipped when I bought a pair of them, but they seem to be incredible. They have a 5 year warranty, each put out 1250 colld cranking amps when I tested them, and, you can run them stone dead if you want, and they bounce right back. Our winters here in my area get very cold and I needed to replace batteries and the starter on my chip truck so I opted for those batteries and a gear reduction starter on my obs powerstroke. I turn the key when its 5 degrees out and that truck cranks over like I hooked it to a nuclear powerplant.
 
My vote is bad batteries, but the flickering ALT light makes everything suspect.

DO NOT EVER DISCONNECT THE BATTERIES WHILE THE TRUCK IS RUNNING. You can actually blow the regulator in the alternator that way, since the circuit loses it's charging reference.
 
It's an old trick from the days of generator charging systems, where it was perfectly okay. On a modern alternator system, removing the BAT terminal takes the reference off the voltage regulator, and it can go wild trying to compensate; alternators are capable of putting out 200 volts or more. And that... is VERY bad for voltage regulators, computers and electronic ignition systems.

Bad batteries are bad for charging systems, too, since the alternator is working overtime to try and keep the battery up and run the loads at times like after starting and at idle, when charging efficiency is low.
 
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I was thinking batteries too, thanks for the replies. I'll run them down to get tested.

I'll probably go with OEM. I'm tired of buying Napa garbage, not regarding the batteries here say, but everything else I've bought from them lately. I hear ups and down about the Optima's too.

My other diesel had OEM batteries, 10+ years old. I've been buying everything OEM lately, the parts just seem to last longer.
 
If you have access to a multi meter, test the alternator at the big wire coming out the back of it. Should read 13 something. Don't expect to see 14. Your auto parts store, as mentioned, should be able to test everything right there in the parking lot. Also, make sure your battery cables and clean and tight, and, like I found out recently, check your engine ground.


Yep. Check the alternator with a voltmeter. If it tests bad take it to auto zone and have them test it as well. I will second the Optima batteries too!
 
13.8 to even 14.8 or 15.0 is normal.

SO pre-computer and electronic ignition it would still be ok?

Not okay; just less stuff to potentially fry. With the old mechanical (relay) regulators, a quick shot to check if the alternator is putting out isn't nearly as much of a concern.
 
It's okay to see a higher charging voltage (and current) right after starting the engine or when there's a lot of load on (ie headlights, AC, etc.). You should see it taper down closer to 13.8 as the charging system tops the battery off or the load reduces.

Butch, you're welcome.
 
You have the 7.3L right? I had the same thing happen to me in the fall and I thought it was the batteries but it ended up being the alternator, batteries were around $250 and the alternator was around $125.
 
There ya go!

FWIW, if it ends up being the alternator, I agree with going OEM. I'm done with aftermarket crap, too.
 
OEM or a local rebuild. The rebuilds from the auto parts store are junk IMO. It sounds like a battery to me. Starting a diesel in cold weather is a big job.
 
Odds are they will test it with one of those load meter battery testers. That tool is a handy thing to have in your shop and don't really cost that much . I think they are under a $ 100 bucks.
 
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