Alternator or battery or both?

[go_deep]

At work till 2030. Will be on it first thing in the morning after my range session. Going to check my grounds and wires and then go pick up a new battery and go from there.

10 4, working late myself. Hope you find an easy fix!

 

[displacedtexan]

He already replaced the alternator. Suggestions that it is the alternator are kind of useless at this point.

For $100-$200, (or whatever it costs nowadays), put in a new battery.

I've had brand new alternators not charge.

 

[Bugger]

Put the leads on the battery while someone starts it up, what does the voltage drop down to at its lowest reading before jumping back up when the alternator kicks in?

 

[insanelupus]

I'm no mechanic, but my buddy is! Lol.

Checking cables, good contact, tight, and corrosion free, great first move.

When the battery was checked, did they just check the top posts? If so, and it's likely a side connect battery, check the battery where the terminals are actually connected.

Just went through this last week. My buddy was smart enough to check both. Top posts tested fine. Side posts were kaput, something inside no good.

Result, new battery, problem solved. Battery was purchased exactly 3 years ago that month.

 

[MistyMountain]

I’ve had problems twice in different cars like the OP described. Had the battery checked at a parts store, looked good, still had problems. Eventually replaced the battery because it was old anyway and all issues were resolved. I don’t know if there’s a common error with testers (seems like a very simple electrical test) or something else, but it’s happened twice to me. And replacing a battery is easier than replacing an alternator .

 

[Ringbill27]

Start it. Check the voltage on the battery. If it’s not 13.5-14.5 volts your alternator is toast. If it is charging your battery is shot. Most car batteries don’t make it past 5years these days. I’d recommend replacing both or at least that’s what I’d do but I don’t my own work.

 

[Ringbill27]

I've had brand new alternators not charge.

This . I’ve swapped alternators and the third one finally charged. These new cheap parts to me seem 50/50 whether they are good. And I’d stay away from alternators from AutoZone.

 

[Geewhiz]

Start it. Check the voltage on the battery. If it’s not 13.5-14.5 volts your alternator is toast. If it is charging your battery is shot. Most car batteries don’t make it past 5years these days. I’d recommend replacing both or at least that’s what I’d do but I don’t my own work.

So a fully charged battery with no load on it should be somewhere around 12-13 volts, correct? And then as soon as the key turns and the starter cranks, drawing from the battery, then how many volts should it read? And then once the engine fires and the starter disengages what should it read?

 

[Bugger]

So a fully charged battery with no load on it should be somewhere around 12-13 volts, correct? And then as soon as the key turns and the starter cranks, drawing from the battery, then how many volts should it read? And then once the engine fires and the starter disengages what should it read?

A good newer battery should drop to 10, maybe a little lower for a single battery in a bigger engine or if it’s old, then go up to 14 if the alternator is working. It’s not an official load test, but gives you a good idea if it’s in decent condition before tracing wires and replacing other parts.
I don’t trust that everyone working in an auto parts store really knows how to work a load tester. But if your old alternator really was bad, then it worked the crap out of that battery on the way out and a slow trickle charge would be preferable to driving it around to revive it on alternator charge.

 

[grfox92]

Hey guys I’m having an issue with my pickup that I need a little help with. Ive never been super savvy with electrical issues.

2010 f150 5.4. Last week everything was just fine, no previous issues with starting. Monday the battery was dead and had to jump 4x throughout the day, I just left it running when I ran errands and it died once when I was in a store. Tuesday morning I went to jump it and as soon as I disconnected the jump pack it died. I did it again and same result, so I drove my other pickup to work. Got a new alternator yesterday evening and put it in and while I was at Napa I had the kid behind the counter test the battery and he said it tested just fine. (Should I trust him or not?)

After installing the new alternator last evening I started it up just fine (with a freshly charged battery) and let it idle but after running for 30mins or so it died again. If I understand correctly, once started shouldn’t it run on the alternator regardless of the status of the battery?

I’m just a bit confused. I think that I likely need a new battery as well but beings as I just got it tested I’m not sure.

Thoughts would be appreciated.

Its a fuse. I had this issue with my 97 F150 4.6. Follow your battery and alternator cables all the way to the firewall. There is a fuse somewhere causing the alternator to not charge the battery. It took my mechanic friend to find it. I checked what I thought were all the fuses and they were good. He found one I missed.

Sent from my SM-G990U using Tapatalk

 

[Ringbill27]

So a fully charged battery with no load on it should be somewhere around 12-13 volts, correct? And then as soon as the key turns and the starter cranks, drawing from the battery, then how many volts should it read? And then once the engine fires and the starter disengages what should it read?

Normally with vehicle off I read 11.8-12.8 volts. Start up voltage is by something I’ve never tested. 13.5-14.5 volts when idling.

 

[Geewhiz]

Here’s where I’m at. I think it’s solved. Somewhat embarrassing but it is what it is.

Load tested the battery and it gave me 13v static and then dropped to 10.2 when the starter was cranking and then went to 12.2 while the pickup was running which means the alternator was not feeding the battery. I then realized that the serpentine belt wasn’t tight and was therefore not spinning the alternator or anything else.

I had to take off the big plastic air intake and a plastic cowl to access the alternator when I replaced it. The tensioner on the serpentine belt is just a spring loaded arm with a pulley on it that you put a half inch breaker bar on and pull it over to relieve the tension and when I replaced the alternator something evidently bound up in the spring mechanism causing the tensioner to not apply adequate tension. I fiddled with the tensioner for a minute and it seams to be working adequately for now.

Started it up again and now was reading 14.5 volts when running so I think we’re ok. Simple and easy but it just wasn’t exactly obvious to me in the dark the other night beneath the air intake and cowling that the belt wasn’t actually spinning.

Off to the auto parts store to grab another serpentine belt but at least I’m not out a battery?

 

[Ringbill27]

Here’s where I’m at. I think it’s solved. Somewhat embarrassing but it is what it is.

Load tested the battery and it gave me 13v static and then dropped to 10.2 when the starter was cranking and then went to 12.2 while the pickup was running which means the alternator was not feeding the battery. I then realized that the serpentine belt wasn’t tight and was therefore not spinning the alternator or anything else.

I had to take off the big plastic air intake and a plastic cowl to access the alternator when I replaced it. The tensioner on the serpentine belt is just a spring loaded arm with a pulley on it that you put a half inch breaker bar on and pull it over to relieve the tension and when I replaced the alternator something evidently bound up in the spring mechanism causing the tensioner to not apply adequate tension. I fiddled with the tensioner for a minute and it seams to be working adequately for now.

Started it up again and now was reading 14.5 volts when running so I think we’re ok. Simple and easy but it just wasn’t exactly obvious to me in the dark the other night beneath the air intake and cowling that the belt wasn’t actually spinning.

Off to the auto parts store to grab another serpentine belt but at least I’m not out a battery?

Sounds good. Easy fix.