1995 4L-v6

Truck not driven a lot (once a week maybe). Battery went dead and wouldn't charge, dead cell. Replaced battery and drove fine a a handful of times over a month. Wouldn't start last week and battery is putting out only 1.8v but it was 12v when I got it. After I replaced it I checked the battery at the terminals while the truck was idle and saw about 14v and assumed the alternator was chagrining.

Now here's the key information:
-I noticed last few drives that the battery gauge is less than half (maybe 1/3rd up) when idle.
-Under acceleration and normal driving it is where it usually is.
-Turning on the AC makes the gauge really drop, even a little further than a 1/3rd, especially at idle.
-I jammed a small sub and a 350 Watt amp in this little single cab truck in 2017 that worked fine last few drives (don't judge me!!)

This is all new and unusual behavior and makes me think the alternator is fried.

I have the battery on a trickle charge and if it charges up I can try to start it. Should I conduct any tests to verify the alternator is bad?

Thanks in advance.

 

Are you sure have there are no power draws while the truck is off? The conditions you describe would also lead me to believe the alternator is done for, given how old it is if its still the stock unit. Your new battery might be junk too, once lead acid batteries get discharged below a certain voltage they become damaged (little crystals start to form on the plates). You can still use them after charging but they wont hold the charge as long. Vehicles you don't drive that often should be on a trickle charger to prevent that discharge.

 

Yes, reads like alternator has 1 or 2 bad fields, there are 3 fields

An alternator can only produce 60% of rated amps at warm engine idle, say 700rpms
So if its a 90amp alternator thats about 54amps
At about 1,800rpms an alternator can produce its full amp rating, 90amps in this example

The 3 Fields are in the case of the alternator, each produces 1/3rd of the rated AMPs
Its not uncommon for older alternator to lose a field and you would notice that as dimming lights at idle, NO, thats not normal on any vehicle, lol

But since engine is not at idle much when driving its usually not a big issue
But if a 2nd field starts to fail then you are down to 18amps at idle and only 30amps above 1,800RPMs
Most vehicles need 40-50amps with everything electrical on

To test start engine and test battery voltage, should be above 14volt just after startup
Now turn on all the lights, AC, door open, and Blower to HIGH
Retest battery voltage, should STILL be above 14volts

If its dropped or dropping then alternator is failing

The battery is ONLY USED to start the engine
The alternator then provides ALL the voltage for the vehicle, plus a little extra to keep battery fully charged
Alternators minimum voltage should be 13.5volts, but over 14v just after startup, it will drop under 14v after 5min or so when battery is recharged

A battery only has 12.8v maximum, 12.3v to 12.8v is its range, so with engine running voltage can only flow TO the battery, so battery shouldn't be used at all
12.8v is a new battery
12.5v is a 3 year old battery
12.3 v is a 5/6 year old battery and time to shop for battery sales
12.2v or less is a drained or failing battery

 

Good advice afkrejci90. My research shows the alternator is right on top of the engine and easily accessible. I may just order one and replace it now.

I have a trickle charger just not in a position where I can have it connected all the time. I would have to pull the battery to leave it on the keeper until I drive it once a week or so.

Decades ago at my grandpa's request I would disconnect the negative terminal for his battery on his old 60's C-10 when he wouldn't drive it much. I was young and just did what I was told. Would that be an acceptable alternative here?.

 

RonD,

I just checked the batter and It looks like the battery is taking a charge on the trickle. If I can get it started I will do the tests you laid out and monitor the output. Reach back later, thanks all!

 

Disconnecting the negative terminal also works too

 

No, not a good idea on 1980 and up vehicles
In the early 1980's we started to get Gen 2 alternators with built in ELECTRONIC voltage regulators
The old voltage regulators were separate and used mechanical relays

Disconnecting either or BOTH battery cables with engine running, and having engine stay running, does mean battery is not being used, which means alternator is supplying all the needed amps/voltage, which is what it should be doing

But when you reconnect the battery there WILL BE a amp/voltage spike, which didn't bother the mechanical relays in the least, but WILL damage electronics in a vehicle
You can get away with it 9 times out of 10, but its that 10th time that can fry a voltage regulator or even the engine computer or any other electronic module, and there are ALOT more of them in newer vehicles

So word to the wise, USE A VOLT METER to test battery and alternator if vehicle is 1980 or newer



Same issue comes up when "jump starting" a newer vehicle, never try to start a vehicle using battery of a running vehicle
You can hookup running vehicles battery to dead battery vehicle and let dead battery charge up, then SHUT OFF the running vehicle, key OFF
Then try to start the dead battery vehicle, using both batteries

You should NEVER connect two electronic charging system together, which is what you are doing if both vehicles are running and you connect the batteries together
i.e. when you start the dead battery vehicle its charging system is now hooked to the running vehicle charging system, and this can "fry" one or both systems

So jumping is fine just do it correctly and your good deed will go unpunished, lol
And again this may not cause an issue 9 times out of 10, but its that 10th time that's totally avoidable if you just do it right

 

I've been doing everything the way you said was wrong lol. I guess I'm just lucky. I did however forget to pop off the negative one time when I was welding on my truck so if that didn't fry any of the electronics I doubt reconnecting the battery will do any harm. If it does thats got to be a an extremely rare occurrence.

 

YUP, but rare ain't NEVER, and it's your time and money on the line, I got no horse in that race, lol

You can drive over a box of roofing nails and not get a flat tire, but in my opinion I would just drive around the box and not take the chance

 

I finally got the battery charged and the truck started right up. When it started up battery read around 14.5+ without anything on. After turning everything I could think of on the battery still read a good 14.5+. I drove it around a little and nothing changed. There is a small blip in the volts when the blower is turned on.

I am confused because last time the volts read much different and the gauge would drop significantly. Is it possible the alternator is going out intermittently? Its a cool night in the mid 60's so not sure that would affect anything. I'm going to monitor the battery over the next weeks or so and see if it drops.

Let me know if I should do anything else, thanks!

 

Test the battery voltage, before starting, after it sits over night, write it down
Then test it the next day after it sits over night, should be exactly the same

After driving for 20+ minutes, the longer the better, do NOT shut off the engine, open hood and test engine running voltage, should be under 14volts, 13.5-13.8v is spec

 

I drove it a few days ago and today the battery is reading 0.11 volts today, it's completely dead. When I parked it, I made sure the ignition was off but two things to note:

1. The hood was latched but not completely closed. I assumed the hood light was off because I think it comes on as the hood raises, but could it have been on?
2. There is an ODB2 sensor plugged in, but it's been plugged in for months. Does it cause a drain on the battery? Could it have drained the battery in 2 days? I thought it only received power while it was on.

Where is the charge going! Is this brand new battery just totally shot?

 

Could try the voltage drop test
Disconnect negative battery terminal. Then attach a volt meter across the negative terminal to body. Make note of voltage. Then pull the fuses on at a time checking for a change in voltage. That can help you find what circuit is shorted if any.

 

No, O2 heaters need to be grounded by computer so can't drain battery if computer is off

Did you do the test in Post #11?

 

RonD

No, I didn't get a chance to. I charged the battery, drove it twice (on the first day and the next day) on short trips and on the third day it was completely dead. I didn't have time between work to drive 20 minutes and do the tests before it went dead. I'll have to charge it again but that will take several days. I'll see what I can do about the tests.

 

After charging do not reconnect battery cables, test voltage on battery, WRITE IT DOWN, and then test voltage again after 8 or more hours, if its lower battery is self draining, yes it can happen to brand new batteries

Batteries have lots of thin plates inside, they alternate + - + - + - + - if some debris gets between 2 plates that's a short, and battery will self drain

 

RonD,

Unplugged the charger and it went from 12.6v to 12.41v in about 5 minutes or less. I'll leave it disconnected from everything and check it later today.

 

Not unusual just after charging, let it sit for a few hours and test again

FYI
12.8v is a new battery
12.5v is a 3 year old battery
12.3v is a 5/6 year old battery, and time to shop for battery sales

 

Here's what it's at now and this battery is just a few months old or less. I think we agree the battery is shot but something else drained it flat I think.

12.6 @ 9:45
12.32 @ 10:40
12.31 @ 11:15
12.29 @ 13:10

 

Yes, that battery has failed, has an internal short that is draining it

And yes, if a car battery is drained it never fully recovers, so repeated draining will finish it off
Car batteries are made with thin plates that can discharge high AMPs quickly and then be re-charged quickly, they are not designed to provide long slow discharges

Deep Cycle batteries have thicker plates and are designed to provide long slow discharges, used in marine and RV applications, to provide power for hours before being recharged

After new battery is in the vehicle and connected, test its voltage, this is "battery voltage"

Use alternator's metal case as the ground for these tests
Test B+ terminal on the back of alternator, the stud/nut terminal, should see battery voltage, if not then MEGA Fuse is bad

Unplug the 3 wire connector on alternator
Test Yellow wire, should see Battery voltage, if not ALT fuse is blown
Test light green wire, should see 0 volts
Turn key ON(engine off)
Re-test light green wire, should see battery voltage, can be a little less, .1 to .2 less, this is also the dashes Battery Light wire, just FYI

If all wires test OK then the vehicle wiring is OK

Start engine
Test battery voltage, should be 14.5 to 14.9 volts, alternator is working, if you see "Battery Voltage" then alternator is bad, because wiring is good

Go for a drive or let engine run for 10min, but don't shut off the engine, retest battery voltage, should be 13.5 to 13.8volts, voltage regulator is working